diff --git a/lib/ASN1/ASNObject.php b/lib/ASN1/ASNObject.php
index d338ad9..de54fb2 100644
--- a/lib/ASN1/ASNObject.php
+++ b/lib/ASN1/ASNObject.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -37,21 +38,22 @@
 use FG\ASN1\Universal\ObjectDescriptor;
 use FG\Utility\BigInteger;
 use LogicException;
+use Stringable;
 
 /**
  * Class ASNObject is the base class for all concrete ASN.1 objects.
  */
-abstract class ASNObject implements Parsable
+abstract class ASNObject implements Parsable, Stringable
 {
-    private $contentLength;
-    private $nrOfLengthOctets;
+    private ?int $contentLength = null;
+    private ?int $nrOfLengthOctets = null;
 
     /**
      * Must return the number of octets of the content part.
      *
      * @return int
      */
-    abstract protected function calculateContentLength();
+    abstract protected function calculateContentLength(): int;
 
     /**
      * Encode the object using DER encoding.
@@ -60,15 +62,15 @@ abstract protected function calculateContentLength();
      *
      * @return string the binary representation of an objects value
      */
-    abstract protected function getEncodedValue();
+    abstract protected function getEncodedValue(): ?string;
 
     /**
      * Return the content of this object in a non encoded form.
-     * This can be used to print the value in human readable form.
+     * This can be used to print the value in human-readable form.
      *
      * @return mixed
      */
-    abstract public function getContent();
+    abstract public function getContent(): mixed;
 
     /**
      * Return the object type octet.
@@ -78,7 +80,7 @@ abstract public function getContent();
      *
      * @return int
      */
-    abstract public function getType();
+    abstract public function getType(): int;
 
     /**
      * Returns all identifier octets. If an inheriting class models a tag with
@@ -89,7 +91,7 @@ abstract public function getType();
      *
      * @return string Identifier as a set of octets
      */
-    public function getIdentifier()
+    public function getIdentifier(): string
     {
         $firstOctet = $this->getType();
 
@@ -105,7 +107,7 @@ public function getIdentifier()
      *
      * @return string the full binary representation of the complete object
      */
-    public function getBinary()
+    public function getBinary(): string
     {
         $result  = $this->getIdentifier();
         $result .= $this->createLengthPart();
@@ -114,7 +116,7 @@ public function getBinary()
         return $result;
     }
 
-    private function createLengthPart()
+    private function createLengthPart(): string
     {
         $contentLength = $this->getContentLength();
         $nrOfLengthOctets = $this->getNumberOfLengthOctets($contentLength);
@@ -132,9 +134,9 @@ private function createLengthPart()
         }
     }
 
-    protected function getNumberOfLengthOctets($contentLength = null)
+    protected function getNumberOfLengthOctets(int $contentLength = null): int
     {
-        if (!isset($this->nrOfLengthOctets)) {
+        if ($this->nrOfLengthOctets === null) {
             if ($contentLength == null) {
                 $contentLength = $this->getContentLength();
             }
@@ -151,16 +153,16 @@ protected function getNumberOfLengthOctets($contentLength = null)
         return $this->nrOfLengthOctets;
     }
 
-    protected function getContentLength()
+    protected function getContentLength(): int
     {
-        if (!isset($this->contentLength)) {
+        if ($this->contentLength === null) {
             $this->contentLength = $this->calculateContentLength();
         }
 
         return $this->contentLength;
     }
 
-    protected function setContentLength($newContentLength)
+    protected function setContentLength(int $newContentLength): void
     {
         $this->contentLength = $newContentLength;
         $this->getNumberOfLengthOctets($newContentLength);
@@ -169,7 +171,7 @@ protected function setContentLength($newContentLength)
     /**
      * Returns the length of the whole object (including the identifier and length octets).
      */
-    public function getObjectLength()
+    public function getObjectLength(): int
     {
         $nrOfIdentifierOctets = strlen($this->getIdentifier());
         $contentLength = $this->getContentLength();
@@ -178,7 +180,7 @@ public function getObjectLength()
         return $nrOfIdentifierOctets + $nrOfLengthOctets + $contentLength;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->getContent();
     }
@@ -188,7 +190,7 @@ public function __toString()
      *
      * @see Identifier::getName()
      */
-    public function getTypeName()
+    public function getTypeName(): string
     {
         return Identifier::getName($this->getType());
     }
@@ -201,7 +203,7 @@ public function getTypeName()
      *
      * @return \FG\ASN1\ASNObject
      */
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         if (strlen($binaryData) <= $offsetIndex) {
             throw new ParserException('Can not parse binary from data: Offset index larger than input size', $offsetIndex);
diff --git a/lib/ASN1/AbstractString.php b/lib/ASN1/AbstractString.php
index 7e0d7dd..09f6cde 100644
--- a/lib/ASN1/AbstractString.php
+++ b/lib/ASN1/AbstractString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -14,81 +15,76 @@
 
 abstract class AbstractString extends ASNObject implements Parsable
 {
-    /** @var string */
-    protected $value;
-    private $checkStringForIllegalChars = true;
-    private $allowedCharacters = [];
+    private bool $checkStringForIllegalChars = true;
+    private array $allowedCharacters = [];
 
     /**
      * The abstract base class for ASN.1 classes which represent some string of character.
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(protected string $value)
     {
-        $this->value = $string;
     }
 
-    public function getContent()
+    public function getContent(): string
     {
         return $this->value;
     }
 
-    protected function allowCharacter($character)
+    protected function allowCharacter(string $character): void
     {
         $this->allowedCharacters[] = $character;
     }
 
-    protected function allowCharacters(...$characters)
+    protected function allowCharacters(string ...$characters): void
     {
         foreach ($characters as $character) {
             $this->allowedCharacters[] = $character;
         }
     }
 
-    protected function allowNumbers()
+    protected function allowNumbers(): void
     {
         foreach (range('0', '9') as $char) {
             $this->allowedCharacters[] = (string) $char;
         }
     }
 
-    protected function allowAllLetters()
+    protected function allowAllLetters(): void
     {
         $this->allowSmallLetters();
         $this->allowCapitalLetters();
     }
 
-    protected function allowSmallLetters()
+    protected function allowSmallLetters(): void
     {
         foreach (range('a', 'z') as $char) {
             $this->allowedCharacters[] = $char;
         }
     }
 
-    protected function allowCapitalLetters()
+    protected function allowCapitalLetters(): void
     {
         foreach (range('A', 'Z') as $char) {
             $this->allowedCharacters[] = $char;
         }
     }
 
-    protected function allowSpaces()
+    protected function allowSpaces(): void
     {
         $this->allowedCharacters[] = ' ';
     }
 
-    protected function allowAll()
+    protected function allowAll(): void
     {
         $this->checkStringForIllegalChars = false;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return strlen($this->value);
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         if ($this->checkStringForIllegalChars) {
             $this->checkString();
@@ -97,18 +93,18 @@ protected function getEncodedValue()
         return $this->value;
     }
 
-    protected function checkString()
+    protected function checkString(): void
     {
         $stringLength = $this->getContentLength();
         for ($i = 0; $i < $stringLength; $i++) {
-            if (in_array($this->value[$i], $this->allowedCharacters) == false) {
+            if (in_array($this->value[$i], $this->allowedCharacters) === false) {
                 $typeName = Identifier::getName($this->getType());
                 throw new Exception("Could not create a {$typeName} from the character sequence '{$this->value}'.");
             }
         }
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         $parsedObject = new static('');
 
diff --git a/lib/ASN1/AbstractTime.php b/lib/ASN1/AbstractTime.php
index f67ef26..5e1dc9c 100644
--- a/lib/ASN1/AbstractTime.php
+++ b/lib/ASN1/AbstractTime.php
@@ -7,20 +7,21 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
 use DateInterval;
 use DateTime;
+use DateTimeInterface;
 use DateTimeZone;
 use Exception;
 
 abstract class AbstractTime extends ASNObject
 {
-    /** @var DateTime */
-    protected $value;
+    protected DateTimeInterface $value;
 
-    public function __construct($dateTime = null, $dateTimeZone = 'UTC')
+    public function __construct(null|string|\DateTimeInterface $dateTime = null, $dateTimeZone = 'UTC')
     {
         if ($dateTime == null || is_string($dateTime)) {
             if (is_null($dateTime)) {
@@ -28,7 +29,7 @@ public function __construct($dateTime = null, $dateTimeZone = 'UTC')
             }
             $timeZone = new DateTimeZone($dateTimeZone);
             $dateTimeObject = new DateTime($dateTime, $timeZone);
-            if ($dateTimeObject == false) {
+            if ($dateTimeObject === false) {
                 $errorMessage = $this->getLastDateTimeErrors();
                 $className = Identifier::getName($this->getType());
                 throw new Exception(sprintf("Could not create %s from date time string '%s': %s", $className, $dateTime, $errorMessage));
@@ -41,12 +42,12 @@ public function __construct($dateTime = null, $dateTimeZone = 'UTC')
         $this->value = $dateTime;
     }
 
-    public function getContent()
+    public function getContent(): \DateTimeInterface
     {
         return $this->value;
     }
 
-    protected function getLastDateTimeErrors()
+    protected function getLastDateTimeErrors(): string
     {
         $messages = '';
         $lastErrors = DateTime::getLastErrors() ?: ['errors' => []];
@@ -57,12 +58,12 @@ protected function getLastDateTimeErrors()
         return substr($messages, 0, -2);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->value->format("Y-m-d\tH:i:s");
     }
 
-    protected static function extractTimeZoneData(&$binaryData, &$offsetIndex, DateTime $dateTime)
+    protected static function extractTimeZoneData(&$binaryData, &$offsetIndex, DateTime $dateTime): \DateTimeInterface
     {
         $sign = $binaryData[$offsetIndex++];
         $timeOffsetHours   = intval(substr($binaryData, $offsetIndex, 2));
diff --git a/lib/ASN1/Base128.php b/lib/ASN1/Base128.php
index 119ee7b..d5874bd 100644
--- a/lib/ASN1/Base128.php
+++ b/lib/ASN1/Base128.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -10,12 +11,7 @@
  */
 class Base128
 {
-    /**
-     * @param int $value
-     *
-     * @return string
-     */
-    public static function encode($value)
+    public static function encode(int $value): string
     {
         $value = BigInteger::create($value);
         $octets = chr($value->modulus(0x80)->toInteger());
@@ -30,13 +26,9 @@ public static function encode($value)
     }
 
     /**
-     * @param string $octets
-     *
      * @throws InvalidArgumentException if the given octets represent a malformed base-128 value or the decoded value would exceed the the maximum integer length
-     *
-     * @return int
      */
-    public static function decode($octets)
+    public static function decode(string $octets): string
     {
         $bitsPerOctet = 7;
         $value = BigInteger::create(0);
diff --git a/lib/ASN1/Composite/AttributeTypeAndValue.php b/lib/ASN1/Composite/AttributeTypeAndValue.php
index 3f4027c..be8b378 100644
--- a/lib/ASN1/Composite/AttributeTypeAndValue.php
+++ b/lib/ASN1/Composite/AttributeTypeAndValue.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Composite;
 
@@ -16,11 +17,7 @@
 
 class AttributeTypeAndValue extends Sequence
 {
-    /**
-     * @param ObjectIdentifier|string $objIdentifier
-     * @param \FG\ASN1\ASNObject $value
-     */
-    public function __construct($objIdentifier, ASNObject $value)
+    public function __construct(ObjectIdentifier|string $objIdentifier, ASNObject $value)
     {
         if ($objIdentifier instanceof ObjectIdentifier == false) {
             $objIdentifier = new ObjectIdentifier($objIdentifier);
@@ -28,7 +25,7 @@ public function __construct($objIdentifier, ASNObject $value)
         parent::__construct($objIdentifier, $value);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->children[0].': '.$this->children[1];
     }
diff --git a/lib/ASN1/Composite/RDNString.php b/lib/ASN1/Composite/RDNString.php
index e95e7ac..8bee3aa 100644
--- a/lib/ASN1/Composite/RDNString.php
+++ b/lib/ASN1/Composite/RDNString.php
@@ -7,20 +7,19 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Composite;
 
+use FG\ASN1\ASNObject;
+use FG\ASN1\Universal\ObjectIdentifier;
 use FG\ASN1\Universal\PrintableString;
 use FG\ASN1\Universal\IA5String;
 use FG\ASN1\Universal\UTF8String;
 
 class RDNString extends RelativeDistinguishedName
 {
-    /**
-     * @param string|\FG\ASN1\Universal\ObjectIdentifier $objectIdentifierString
-     * @param string|\FG\ASN1\ASNObject $value
-     */
-    public function __construct($objectIdentifierString, $value)
+    public function __construct(string|ObjectIdentifier $objectIdentifierString, string|ASNObject $value)
     {
         if (PrintableString::isValid($value)) {
             $value = new PrintableString($value);
diff --git a/lib/ASN1/Composite/RelativeDistinguishedName.php b/lib/ASN1/Composite/RelativeDistinguishedName.php
index 4185f41..e0ba462 100644
--- a/lib/ASN1/Composite/RelativeDistinguishedName.php
+++ b/lib/ASN1/Composite/RelativeDistinguishedName.php
@@ -7,27 +7,25 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Composite;
 
 use FG\ASN1\Exception\NotImplementedException;
 use FG\ASN1\ASNObject;
+use FG\ASN1\Universal\ObjectIdentifier;
 use FG\ASN1\Universal\Set;
 
 class RelativeDistinguishedName extends Set
 {
-    /**
-     * @param string|\FG\ASN1\Universal\ObjectIdentifier $objIdentifierString
-     * @param \FG\ASN1\ASNObject $value
-     */
-    public function __construct($objIdentifierString, ASNObject $value)
+    public function __construct(string|ObjectIdentifier $objIdentifierString, ASNObject $value)
     {
         // TODO: This does only support one element in the RelativeDistinguishedName Set but it it is defined as follows:
         // RelativeDistinguishedName ::= SET SIZE (1..MAX) OF AttributeTypeAndValue
         parent::__construct(new AttributeTypeAndValue($objIdentifierString, $value));
     }
 
-    public function getContent()
+    public function getContent(): string
     {
         /** @var \FG\ASN1\ASNObject $firstObject */
         $firstObject = $this->children[0];
@@ -43,7 +41,7 @@ public function getContent()
      * @param int $offsetIndex
      * @throws NotImplementedException
      */
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         throw new NotImplementedException();
     }
diff --git a/lib/ASN1/Construct.php b/lib/ASN1/Construct.php
index cedf422..2452909 100644
--- a/lib/ASN1/Construct.php
+++ b/lib/ASN1/Construct.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -18,68 +19,59 @@
 
 abstract class Construct extends ASNObject implements Countable, ArrayAccess, Iterator, Parsable
 {
-    /** @var \FG\ASN1\ASNObject[] */
-    protected $children;
-    private $iteratorPosition;
+    /** @var ASNObject[] */
+    protected array $children;
+    private int $iteratorPosition = 0;
 
     /**
-     * @param \FG\ASN1\ASNObject[] $children the variadic type hint is commented due to https://github.com/facebook/hhvm/issues/4858
+     * @param ASNObject[] $children the variadic type hint is commented due to https://github.com/facebook/hhvm/issues/4858
      */
-    public function __construct(/* HH_FIXME[4858]: variadic + strict */ ...$children)
+    public function __construct(ASNObject ...$children)
     {
         $this->children = $children;
-        $this->iteratorPosition = 0;
     }
 
-    public function getContent()
+    public function getContent(): mixed
     {
         return $this->children;
     }
 
-    #[\ReturnTypeWillChange]
-    public function rewind()
+    public function rewind(): void
     {
         $this->iteratorPosition = 0;
     }
 
-    #[\ReturnTypeWillChange]
-    public function current()
+    public function current(): ASNObject
     {
         return $this->children[$this->iteratorPosition];
     }
 
-    #[\ReturnTypeWillChange]
-    public function key()
+    public function key(): int
     {
         return $this->iteratorPosition;
     }
 
-    #[\ReturnTypeWillChange]
-    public function next()
+    public function next(): void
     {
         $this->iteratorPosition++;
     }
 
-    #[\ReturnTypeWillChange]
-    public function valid()
+    public function valid(): bool
     {
         return isset($this->children[$this->iteratorPosition]);
     }
 
-    #[\ReturnTypeWillChange]
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return array_key_exists($offset, $this->children);
     }
 
-    #[\ReturnTypeWillChange]
-    public function offsetGet($offset)
+    public function offsetGet($offset): ASNObject
     {
         return $this->children[$offset];
     }
 
-    #[\ReturnTypeWillChange]
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         if ($offset === null) {
             $offset = count($this->children);
@@ -88,13 +80,12 @@ public function offsetSet($offset, $value)
         $this->children[$offset] = $value;
     }
 
-    #[\ReturnTypeWillChange]
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         unset($this->children[$offset]);
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         $length = 0;
         foreach ($this->children as $component) {
@@ -104,7 +95,7 @@ protected function calculateContentLength()
         return $length;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         $result = '';
         foreach ($this->children as $component) {
@@ -114,19 +105,19 @@ protected function getEncodedValue()
         return $result;
     }
 
-    public function addChild(ASNObject $child)
+    public function addChild(ASNObject $child): void
     {
         $this->children[] = $child;
     }
 
-    public function addChildren(array $children)
+    public function addChildren(array $children): void
     {
         foreach ($children as $child) {
             $this->addChild($child);
         }
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         $nrOfChildren = $this->getNumberOfChildren();
         $childString = $nrOfChildren == 1 ? 'child' : 'children';
@@ -134,23 +125,23 @@ public function __toString()
         return "[{$nrOfChildren} {$childString}]";
     }
 
-    public function getNumberOfChildren()
+    public function getNumberOfChildren(): int
     {
         return count($this->children);
     }
 
     /**
-     * @return \FG\ASN1\ASNObject[]
+     * @return ASNObject[]
      */
-    public function getChildren()
+    public function getChildren(): array
     {
         return $this->children;
     }
 
     /**
-     * @return \FG\ASN1\ASNObject
+     * @return ASNObject
      */
-    public function getFirstChild()
+    public function getFirstChild(): ASNObject
     {
         return $this->children[0];
     }
@@ -163,8 +154,7 @@ public function getFirstChild()
      *
      * @return Construct|static
      */
-    #[\ReturnTypeWillChange]
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         $parsedObject = new static();
         self::parseIdentifier($binaryData[$offsetIndex], $parsedObject->getType(), $offsetIndex++);
@@ -189,13 +179,12 @@ public static function fromBinary(&$binaryData, &$offsetIndex = 0)
         return $parsedObject;
     }
 
-    #[\ReturnTypeWillChange]
-    public function count($mode = COUNT_NORMAL)
+    public function count($mode = COUNT_NORMAL): int
     {
         return count($this->children, $mode);
     }
 
-    public function getIterator()
+    public function getIterator(): \ArrayIterator
     {
         return new ArrayIterator($this->children);
     }
diff --git a/lib/ASN1/Exception/NotImplementedException.php b/lib/ASN1/Exception/NotImplementedException.php
index c9f8e82..2992a53 100644
--- a/lib/ASN1/Exception/NotImplementedException.php
+++ b/lib/ASN1/Exception/NotImplementedException.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Exception;
 
diff --git a/lib/ASN1/Exception/ParserException.php b/lib/ASN1/Exception/ParserException.php
index 4bda4e8..07a4916 100644
--- a/lib/ASN1/Exception/ParserException.php
+++ b/lib/ASN1/Exception/ParserException.php
@@ -7,22 +7,18 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Exception;
 
 class ParserException extends \Exception
 {
-    private $errorMessage;
-    private $offset;
-
-    public function __construct($errorMessage, $offset)
+    public function __construct(private string $errorMessage, private int $offset)
     {
-        $this->errorMessage = $errorMessage;
-        $this->offset = $offset;
         parent::__construct("ASN.1 Parser Exception at offset {$this->offset}: {$this->errorMessage}");
     }
 
-    public function getOffset()
+    public function getOffset(): int
     {
         return $this->offset;
     }
diff --git a/lib/ASN1/ExplicitlyTaggedObject.php b/lib/ASN1/ExplicitlyTaggedObject.php
index b947a95..2f42a7d 100644
--- a/lib/ASN1/ExplicitlyTaggedObject.php
+++ b/lib/ASN1/ExplicitlyTaggedObject.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -31,21 +32,15 @@
  */
 class ExplicitlyTaggedObject extends ASNObject
 {
-    /** @var \FG\ASN1\ASNObject[] */
-    private $decoratedObjects;
-    private $tag;
-
-    /**
-     * @param int $tag
-     * @param \FG\ASN1\ASNObject $objects,...
-     */
-    public function __construct($tag, /* HH_FIXME[4858]: variadic + strict */ ...$objects)
+    /** @var ASNObject[] */
+    private array $decoratedObjects;
+
+    public function __construct(private string|int $tag, ASNObject ...$objects)
     {
-        $this->tag = $tag;
         $this->decoratedObjects = $objects;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         $length = 0;
         foreach ($this->decoratedObjects as $object) {
@@ -55,7 +50,7 @@ protected function calculateContentLength()
         return $length;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         $encoded = '';
         foreach ($this->decoratedObjects as $object) {
@@ -65,12 +60,12 @@ protected function getEncodedValue()
         return $encoded;
     }
 
-    public function getContent()
+    public function getContent(): array
     {
         return $this->decoratedObjects;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         switch ($length = count($this->decoratedObjects)) {
         case 0:
@@ -83,24 +78,24 @@ public function __toString()
         }
     }
 
-    public function getType()
+    public function getType(): int
     {
         return ord($this->getIdentifier());
     }
 
-    public function getIdentifier()
+    public function getIdentifier(): string
     {
         $identifier = Identifier::create(Identifier::CLASS_CONTEXT_SPECIFIC, true, $this->tag);
 
         return is_int($identifier) ? chr($identifier) : $identifier;
     }
 
-    public function getTag()
+    public function getTag(): int
     {
         return $this->tag;
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         $identifier = self::parseBinaryIdentifier($binaryData, $offsetIndex);
         $firstIdentifierOctet = ord($identifier);
diff --git a/lib/ASN1/Identifier.php b/lib/ASN1/Identifier.php
index b21caa3..869a440 100644
--- a/lib/ASN1/Identifier.php
+++ b/lib/ASN1/Identifier.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -71,15 +72,9 @@ class Identifier
      * Creates an identifier. Short form identifiers are returned as integers
      * for BC, long form identifiers will be returned as a string of octets.
      *
-     * @param int $class
-     * @param bool $isConstructed
-     * @param int $tagNumber
-     *
      * @throws Exception if the given arguments are invalid
-     *
-     * @return int|string
      */
-    public static function create($class, $isConstructed, $tagNumber)
+    public static function create(int $class, bool $isConstructed, int|string $tagNumber): int|string
     {
         if (!is_numeric($class) || $class < self::CLASS_UNIVERSAL || $class > self::CLASS_PRIVATE) {
             throw new Exception(sprintf('Invalid class %d given', $class));
@@ -104,12 +99,12 @@ public static function create($class, $isConstructed, $tagNumber)
         return chr($firstOctet).Base128::encode($tagNumber);
     }
 
-    public static function isConstructed($identifierOctet)
+    public static function isConstructed(int $identifierOctet): bool
     {
         return ($identifierOctet & self::IS_CONSTRUCTED) === self::IS_CONSTRUCTED;
     }
 
-    public static function isLongForm($identifierOctet)
+    public static function isLongForm(int $identifierOctet): bool
     {
         return ($identifierOctet & self::LONG_FORM) === self::LONG_FORM;
     }
@@ -120,12 +115,8 @@ public static function isLongForm($identifierOctet)
      * Example: ASN.1 Octet String
      *
      * @see Identifier::getShortName()
-     *
-     * @param int|string $identifier
-     *
-     * @return string
      */
-    public static function getName($identifier)
+    public static function getName(int|string $identifier): string
     {
         $identifierOctet = self::makeNumeric($identifier);
 
@@ -147,12 +138,8 @@ public static function getName($identifier)
      *
      * @see Identifier::getName()
      * @see Identifier::getClassDescription()
-     *
-     * @param int|string $identifier
-     *
-     * @return string
      */
-    public static function getShortName($identifier)
+    public static function getShortName(int|string $identifier): string
     {
         $identifierOctet = self::makeNumeric($identifier);
 
@@ -243,12 +230,8 @@ public static function getShortName($identifier)
      * Example:
      *     Constructed context-specific
      *     Primitive universal
-     *
-     * @param int|string $identifier
-     *
-     * @return string
      */
-    public static function getClassDescription($identifier)
+    public static function getClassDescription(int|string $identifier): string
     {
         $identifierOctet = self::makeNumeric($identifier);
 
@@ -280,12 +263,7 @@ public static function getClassDescription($identifier)
         return $classDescription;
     }
 
-    /**
-     * @param int|string $identifier
-     *
-     * @return int
-     */
-    public static function getTagNumber($identifier)
+    public static function getTagNumber(string|int $identifier): string|int
     {
         $firstOctet = self::makeNumeric($identifier);
         $tagNumber = $firstOctet & self::LONG_FORM;
@@ -300,35 +278,35 @@ public static function getTagNumber($identifier)
         return Base128::decode(substr($identifier, 1));
     }
 
-    public static function isUniversalClass($identifier)
+    public static function isUniversalClass(string|int $identifier): bool
     {
         $identifier = self::makeNumeric($identifier);
 
         return $identifier >> 6 == self::CLASS_UNIVERSAL;
     }
 
-    public static function isApplicationClass($identifier)
+    public static function isApplicationClass(string|int $identifier): bool
     {
         $identifier = self::makeNumeric($identifier);
 
         return $identifier >> 6 == self::CLASS_APPLICATION;
     }
 
-    public static function isContextSpecificClass($identifier)
+    public static function isContextSpecificClass(string|int $identifier): bool
     {
         $identifier = self::makeNumeric($identifier);
 
         return $identifier >> 6 == self::CLASS_CONTEXT_SPECIFIC;
     }
 
-    public static function isPrivateClass($identifier)
+    public static function isPrivateClass(string|int $identifier): bool
     {
         $identifier = self::makeNumeric($identifier);
 
         return $identifier >> 6 == self::CLASS_PRIVATE;
     }
 
-    private static function makeNumeric($identifierOctet)
+    private static function makeNumeric(int|string $identifierOctet): int
     {
         if (!is_numeric($identifierOctet)) {
             return ord($identifierOctet);
diff --git a/lib/ASN1/OID.php b/lib/ASN1/OID.php
index bfaeae1..2624b27 100644
--- a/lib/ASN1/OID.php
+++ b/lib/ASN1/OID.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -69,14 +70,9 @@ class OID
      * query http://oid-info.com for the right name.
      * This behavior can be suppressed by setting the second method parameter to false.
      *
-     * @param string $oidString
-     * @param bool $loadFromWeb
-     *
      * @see self::loadFromWeb($oidString)
-     *
-     * @return string
      */
-    public static function getName($oidString, $loadFromWeb = true)
+    public static function getName(string $oidString, bool $loadFromWeb = true): string
     {
         $oids = [
             '1.2' => 'ISO Member Body',
@@ -998,7 +994,7 @@ public static function getName($oidString, $loadFromWeb = true)
         }
     }
 
-    public static function loadFromWeb($oidString)
+    public static function loadFromWeb(string $oidString): string
     {
         $ch = curl_init("http://oid-info.com/get/{$oidString}");
 
diff --git a/lib/ASN1/Parsable.php b/lib/ASN1/Parsable.php
index fa66b55..27fd4f5 100644
--- a/lib/ASN1/Parsable.php
+++ b/lib/ASN1/Parsable.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -28,5 +29,5 @@ interface Parsable
      *
      * @return static
      */
-    public static function fromBinary(&$binaryData, &$offsetIndex = null);
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static;
 }
diff --git a/lib/ASN1/TemplateParser.php b/lib/ASN1/TemplateParser.php
index 90a40b0..a1f6658 100644
--- a/lib/ASN1/TemplateParser.php
+++ b/lib/ASN1/TemplateParser.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
@@ -17,24 +18,18 @@
 class TemplateParser
 {
     /**
-     * @param string $data
-     * @param array $template
-     * @return \FG\ASN1\ASNObject|Sequence
      * @throws ParserException if there was an issue parsing
      */
-    public function parseBase64($data, array $template)
+    public function parseBase64(string $data, array $template): ASNObject|Sequence
     {
         // TODO test with invalid data
         return $this->parseBinary(base64_decode($data), $template);
     }
 
     /**
-     * @param string $binary
-     * @param array $template
-     * @return \FG\ASN1\ASNObject|Sequence
      * @throws ParserException if there was an issue parsing
      */
-    public function parseBinary($binary, array $template)
+    public function parseBinary(string $binary, array $template): ASNObject|Sequence
     {
         $parsedObject = ASNObject::fromBinary($binary);
 
@@ -45,7 +40,7 @@ public function parseBinary($binary, array $template)
         return $parsedObject;
     }
 
-    private function validate(ASNObject $object, $key, $value)
+    private function validate(ASNObject $object, $key, $value): void
     {
         if (is_array($value)) {
             $this->assertTypeId($key, $object);
@@ -60,7 +55,7 @@ private function validate(ASNObject $object, $key, $value)
         }
     }
 
-    private function assertTypeId($expectedTypeId, ASNObject $object)
+    private function assertTypeId(int $expectedTypeId, ASNObject $object): void
     {
         $actualType = $object->getType();
         if ($expectedTypeId != $actualType) {
diff --git a/lib/ASN1/Universal/BMPString.php b/lib/ASN1/Universal/BMPString.php
index 83ec6a9..0d327a0 100644
--- a/lib/ASN1/Universal/BMPString.php
+++ b/lib/ASN1/Universal/BMPString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -25,16 +26,14 @@ class BMPString extends AbstractString
      * characters outside the Basic Multilingual Plane) of ISO/IEC 10646-1.
      *
      * TODO The encodable characters of this type are not yet checked.
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::BMP_STRING;
     }
diff --git a/lib/ASN1/Universal/BitString.php b/lib/ASN1/Universal/BitString.php
index 226695c..825110d 100644
--- a/lib/ASN1/Universal/BitString.php
+++ b/lib/ASN1/Universal/BitString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -17,8 +18,6 @@
 
 class BitString extends OctetString implements Parsable
 {
-    private $nrOfUnusedBits;
-
     /**
      * Creates a new ASN.1 BitString object.
      *
@@ -27,29 +26,27 @@ class BitString extends OctetString implements Parsable
      *
      * @throws Exception if the second parameter is no positive numeric value
      */
-    public function __construct($value, $nrOfUnusedBits = 0)
+    public function __construct(string|int $value, private int $nrOfUnusedBits = 0)
     {
         parent::__construct($value);
 
         if (!is_numeric($nrOfUnusedBits) || $nrOfUnusedBits < 0) {
             throw new Exception('BitString: second parameter needs to be a positive number (or zero)!');
         }
-
-        $this->nrOfUnusedBits = $nrOfUnusedBits;
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::BITSTRING;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         // add one to the length for the first octet which encodes the number of unused bits in the last octet
         return parent::calculateContentLength() + 1;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         // the first octet determines the number of unused bits
         $nrOfUnusedBitsOctet = chr($this->nrOfUnusedBits);
@@ -58,12 +55,12 @@ protected function getEncodedValue()
         return $nrOfUnusedBitsOctet.$actualContent;
     }
 
-    public function getNumberOfUnusedBits()
+    public function getNumberOfUnusedBits(): int
     {
         return $this->nrOfUnusedBits;
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::BITSTRING, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex, 2);
diff --git a/lib/ASN1/Universal/Boolean.php b/lib/ASN1/Universal/Boolean.php
index b73c99f..2491a8f 100644
--- a/lib/ASN1/Universal/Boolean.php
+++ b/lib/ASN1/Universal/Boolean.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -17,45 +18,39 @@
 
 class Boolean extends ASNObject implements Parsable
 {
-    private $value;
-
-    /**
-     * @param bool $value
-     */
-    public function __construct($value)
+    public function __construct(private bool $value)
     {
-        $this->value = $value;
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::BOOLEAN;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return 1;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): string
     {
-        if ($this->value == false) {
+        if ($this->value === false) {
             return chr(0x00);
         } else {
             return chr(0xFF);
         }
     }
 
-    public function getContent()
+    public function getContent(): string
     {
-        if ($this->value == true) {
+        if ($this->value === true) {
             return 'TRUE';
         } else {
             return 'FALSE';
         }
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::BOOLEAN, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex);
diff --git a/lib/ASN1/Universal/CharacterString.php b/lib/ASN1/Universal/CharacterString.php
index bfc170d..f67ddc1 100644
--- a/lib/ASN1/Universal/CharacterString.php
+++ b/lib/ASN1/Universal/CharacterString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -15,13 +16,13 @@
 
 class CharacterString extends AbstractString
 {
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::CHARACTER_STRING;
     }
diff --git a/lib/ASN1/Universal/Enumerated.php b/lib/ASN1/Universal/Enumerated.php
index 06d04a3..d7310cb 100644
--- a/lib/ASN1/Universal/Enumerated.php
+++ b/lib/ASN1/Universal/Enumerated.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -14,7 +15,7 @@
 
 class Enumerated extends Integer
 {
-    public function getType()
+    public function getType(): int
     {
         return Identifier::ENUMERATED;
     }
diff --git a/lib/ASN1/Universal/GeneralString.php b/lib/ASN1/Universal/GeneralString.php
index fb0346f..60fe0b0 100644
--- a/lib/ASN1/Universal/GeneralString.php
+++ b/lib/ASN1/Universal/GeneralString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -18,16 +19,14 @@ class GeneralString extends AbstractString
     /**
      * Creates a new ASN.1 GeneralString.
      * TODO The encodable characters of this type are not yet checked.
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::GENERAL_STRING;
     }
diff --git a/lib/ASN1/Universal/GeneralizedTime.php b/lib/ASN1/Universal/GeneralizedTime.php
index ca92209..e0332fc 100644
--- a/lib/ASN1/Universal/GeneralizedTime.php
+++ b/lib/ASN1/Universal/GeneralizedTime.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -40,12 +41,12 @@ public function __construct($dateTime = null, $dateTimeZone = 'UTC')
         }
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::GENERALIZED_TIME;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         $contentSize = 15; // YYYYMMDDHHmmSSZ
 
@@ -56,12 +57,12 @@ protected function calculateContentLength()
         return $contentSize;
     }
 
-    public function containsFractionalSecondsElement()
+    public function containsFractionalSecondsElement(): bool
     {
         return intval($this->microseconds) > 0;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         $encodedContent = $this->value->format('YmdHis');
         if ($this->containsFractionalSecondsElement()) {
@@ -71,7 +72,7 @@ protected function getEncodedValue()
         return $encodedContent.'Z';
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         if ($this->containsFractionalSecondsElement()) {
             return $this->value->format("Y-m-d\tH:i:s.uP");
@@ -80,7 +81,7 @@ public function __toString()
         }
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::GENERALIZED_TIME, $offsetIndex++);
         $lengthOfMinimumTimeString = 14; // YYYYMMDDHHmmSS
diff --git a/lib/ASN1/Universal/GraphicString.php b/lib/ASN1/Universal/GraphicString.php
index 4a01d67..bff6405 100644
--- a/lib/ASN1/Universal/GraphicString.php
+++ b/lib/ASN1/Universal/GraphicString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -18,16 +19,14 @@ class GraphicString extends AbstractString
     /**
      * Creates a new ASN.1 Graphic String.
      * TODO The encodable characters of this type are not yet checked.
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::GRAPHIC_STRING;
     }
diff --git a/lib/ASN1/Universal/IA5String.php b/lib/ASN1/Universal/IA5String.php
index 33a8067..7d8982b 100644
--- a/lib/ASN1/Universal/IA5String.php
+++ b/lib/ASN1/Universal/IA5String.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -28,7 +29,7 @@ public function __construct($string)
         }
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::IA5_STRING;
     }
diff --git a/lib/ASN1/Universal/Integer.php b/lib/ASN1/Universal/Integer.php
index fe3806b..93006a2 100644
--- a/lib/ASN1/Universal/Integer.php
+++ b/lib/ASN1/Universal/Integer.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -19,38 +20,32 @@
 
 class Integer extends ASNObject implements Parsable
 {
-    /** @var int */
-    private $value;
-
     /**
-     * @param int $value
-     *
      * @throws Exception if the value is not numeric
      */
-    public function __construct($value)
+    public function __construct(private string|int $value)
     {
         if (is_numeric($value) == false) {
             throw new Exception("Invalid VALUE [{$value}] for ASN1_INTEGER");
         }
-        $this->value = $value;
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::INTEGER;
     }
 
-    public function getContent()
+    public function getContent(): string|int
     {
         return $this->value;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return strlen($this->getEncodedValue());
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         $value = BigInteger::create($this->value, 10);
         $negative = $value->compare(0) < 0;
@@ -92,7 +87,7 @@ protected function getEncodedValue()
         return $r;
     }
 
-    private static function ensureMinimalEncoding($binaryData, $offsetIndex)
+    private static function ensureMinimalEncoding($binaryData, $offsetIndex): void
     {
         // All the first nine bits cannot equal 0 or 1, which would
         // be non-minimal encoding for positive and negative integers respectively
@@ -102,7 +97,7 @@ private static function ensureMinimalEncoding($binaryData, $offsetIndex)
         }
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         $parsedObject = new static(0);
         self::parseIdentifier($binaryData[$offsetIndex], $parsedObject->getType(), $offsetIndex++);
diff --git a/lib/ASN1/Universal/NullObject.php b/lib/ASN1/Universal/NullObject.php
index b5293e4..ec25c5b 100644
--- a/lib/ASN1/Universal/NullObject.php
+++ b/lib/ASN1/Universal/NullObject.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -17,27 +18,27 @@
 
 class NullObject extends ASNObject implements Parsable
 {
-    public function getType()
+    public function getType(): int
     {
         return Identifier::NULL;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return 0;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         return null;
     }
 
-    public function getContent()
+    public function getContent(): string
     {
         return 'NULL';
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::NULL, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex);
diff --git a/lib/ASN1/Universal/NumericString.php b/lib/ASN1/Universal/NumericString.php
index 13fb7c3..8a7b50b 100644
--- a/lib/ASN1/Universal/NumericString.php
+++ b/lib/ASN1/Universal/NumericString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -21,17 +22,15 @@ class NumericString extends AbstractString
      * The following characters are permitted:
      * Digits                0,1, ... 9
      * SPACE                 (space)
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowNumbers();
         $this->allowSpaces();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::NUMERIC_STRING;
     }
diff --git a/lib/ASN1/Universal/ObjectDescriptor.php b/lib/ASN1/Universal/ObjectDescriptor.php
index 1c5d349..f2ab925 100644
--- a/lib/ASN1/Universal/ObjectDescriptor.php
+++ b/lib/ASN1/Universal/ObjectDescriptor.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -14,12 +15,12 @@
 
 class ObjectDescriptor extends GraphicString
 {
-    public function __construct($objectDescription)
+    public function __construct(string $objectDescription)
     {
         parent::__construct($objectDescription);
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::OBJECT_DESCRIPTOR;
     }
diff --git a/lib/ASN1/Universal/ObjectIdentifier.php b/lib/ASN1/Universal/ObjectIdentifier.php
index 150ce9c..9b635cc 100644
--- a/lib/ASN1/Universal/ObjectIdentifier.php
+++ b/lib/ASN1/Universal/ObjectIdentifier.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -20,8 +21,8 @@
 
 class ObjectIdentifier extends ASNObject implements Parsable
 {
-    protected $subIdentifiers;
-    protected $value;
+    protected array $subIdentifiers;
+    protected string $value;
 
     public function __construct($value)
     {
@@ -46,17 +47,17 @@ public function __construct($value)
         $this->value = $value;
     }
 
-    public function getContent()
+    public function getContent(): string
     {
         return $this->value;
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::OBJECT_IDENTIFIER;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         $length = 0;
         foreach ($this->subIdentifiers as $subIdentifier) {
@@ -69,7 +70,7 @@ protected function calculateContentLength()
         return $length;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         $encodedValue = '';
         foreach ($this->subIdentifiers as $subIdentifier) {
@@ -79,12 +80,12 @@ protected function getEncodedValue()
         return $encodedValue;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return OID::getName($this->value);
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::OBJECT_IDENTIFIER, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex, 1);
@@ -104,15 +105,9 @@ public static function fromBinary(&$binaryData, &$offsetIndex = 0)
      * differently. This way relative object identifiers can also be parsed
      * using this.
      *
-     * @param $binaryData
-     * @param $offsetIndex
-     * @param $octetsToRead
-     *
      * @throws ParserException
-     *
-     * @return string
      */
-    protected static function parseOid(&$binaryData, &$offsetIndex, $octetsToRead)
+    protected static function parseOid(string &$binaryData, int &$offsetIndex, int $octetsToRead): string
     {
         $oid = '';
 
diff --git a/lib/ASN1/Universal/OctetString.php b/lib/ASN1/Universal/OctetString.php
index e12e722..40594d3 100644
--- a/lib/ASN1/Universal/OctetString.php
+++ b/lib/ASN1/Universal/OctetString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -17,7 +18,7 @@
 
 class OctetString extends ASNObject implements Parsable
 {
-    protected $value;
+    protected ?string $value = null;
 
     public function __construct($value)
     {
@@ -40,12 +41,12 @@ public function __construct($value)
         $this->value = $value;
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::OCTETSTRING;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         if (is_null($this->value)) {
             return 0;
@@ -53,7 +54,7 @@ protected function calculateContentLength()
         return strlen($this->value) / 2;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         $value = $this->value;
         if (is_null($value)) {
@@ -72,7 +73,7 @@ protected function getEncodedValue()
         return $result;
     }
 
-    public function getContent()
+    public function getContent(): string
     {
         if (is_null($this->value)) {
             return '';
@@ -80,12 +81,12 @@ public function getContent()
         return strtoupper($this->value);
     }
 
-    public function getBinaryContent()
+    public function getBinaryContent(): string
     {
         return $this->getEncodedValue();
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::OCTETSTRING, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex);
diff --git a/lib/ASN1/Universal/PrintableString.php b/lib/ASN1/Universal/PrintableString.php
index fe6d4bc..a941073 100644
--- a/lib/ASN1/Universal/PrintableString.php
+++ b/lib/ASN1/Universal/PrintableString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -34,19 +35,17 @@ class PrintableString extends AbstractString
      * COLON                 :
      * EQUALS SIGN           =
      * QUESTION MARK         ?
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowNumbers();
         $this->allowAllLetters();
         $this->allowSpaces();
         $this->allowCharacters("'", '(', ')', '+', '-', '.', ',', '/', ':', '=', '?');
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::PRINTABLE_STRING;
     }
diff --git a/lib/ASN1/Universal/RelativeObjectIdentifier.php b/lib/ASN1/Universal/RelativeObjectIdentifier.php
index 2aa9643..8185074 100644
--- a/lib/ASN1/Universal/RelativeObjectIdentifier.php
+++ b/lib/ASN1/Universal/RelativeObjectIdentifier.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -33,12 +34,12 @@ public function __construct($subIdentifiers)
         }
     }
 
-    public function getType()
+    public function getType():int
     {
         return Identifier::RELATIVE_OID;
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::RELATIVE_OID, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex, 1);
diff --git a/lib/ASN1/Universal/Sequence.php b/lib/ASN1/Universal/Sequence.php
index 0397cf1..c4ad3b4 100644
--- a/lib/ASN1/Universal/Sequence.php
+++ b/lib/ASN1/Universal/Sequence.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -16,7 +17,7 @@
 
 class Sequence extends Construct implements Parsable
 {
-    public function getType()
+    public function getType(): int
     {
         return Identifier::SEQUENCE;
     }
diff --git a/lib/ASN1/Universal/Set.php b/lib/ASN1/Universal/Set.php
index 6e6d346..6d7d332 100644
--- a/lib/ASN1/Universal/Set.php
+++ b/lib/ASN1/Universal/Set.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -14,7 +15,7 @@
 
 class Set extends Sequence
 {
-    public function getType()
+    public function getType(): int
     {
         return Identifier::SET;
     }
diff --git a/lib/ASN1/Universal/T61String.php b/lib/ASN1/Universal/T61String.php
index 5641864..588de8c 100644
--- a/lib/ASN1/Universal/T61String.php
+++ b/lib/ASN1/Universal/T61String.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -20,16 +21,14 @@ class T61String extends AbstractString
      * TODO The encodable characters of this type are not yet checked.
      *
      * @see http://en.wikipedia.org/wiki/ITU_T.61
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::T61_STRING;
     }
diff --git a/lib/ASN1/Universal/UTCTime.php b/lib/ASN1/Universal/UTCTime.php
index c4d303c..397316a 100644
--- a/lib/ASN1/Universal/UTCTime.php
+++ b/lib/ASN1/Universal/UTCTime.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -26,22 +27,22 @@
  */
 class UTCTime extends AbstractTime implements Parsable
 {
-    public function getType()
+    public function getType(): int
     {
         return Identifier::UTC_TIME;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return 13; // Content is a string o the following format: YYMMDDhhmmssZ (13 octets)
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         return $this->value->format('ymdHis').'Z';
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::UTC_TIME, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex, 11);
diff --git a/lib/ASN1/Universal/UTF8String.php b/lib/ASN1/Universal/UTF8String.php
index cba568d..b787ba6 100644
--- a/lib/ASN1/Universal/UTF8String.php
+++ b/lib/ASN1/Universal/UTF8String.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -18,16 +19,14 @@ class UTF8String extends AbstractString
     /**
      * Creates a new ASN.1 Universal String.
      * TODO The encodable characters of this type are not yet checked.
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::UTF8_STRING;
     }
diff --git a/lib/ASN1/Universal/UniversalString.php b/lib/ASN1/Universal/UniversalString.php
index 0c3fe1d..10f6ae6 100644
--- a/lib/ASN1/Universal/UniversalString.php
+++ b/lib/ASN1/Universal/UniversalString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -20,16 +21,14 @@ class UniversalString extends AbstractString
      * TODO The encodable characters of this type are not yet checked.
      *
      * @see http://en.wikipedia.org/wiki/Universal_Character_Set
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::UNIVERSAL_STRING;
     }
diff --git a/lib/ASN1/Universal/VisibleString.php b/lib/ASN1/Universal/VisibleString.php
index d9326d3..38fa4ad 100644
--- a/lib/ASN1/Universal/VisibleString.php
+++ b/lib/ASN1/Universal/VisibleString.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1\Universal;
 
@@ -18,16 +19,14 @@ class VisibleString extends AbstractString
     /**
      * Creates a new ASN.1 Visible String.
      * TODO The encodable characters of this type are not yet checked.
-     *
-     * @param string $string
      */
-    public function __construct($string)
+    public function __construct(string $string)
     {
-        $this->value = $string;
+        parent::__construct($string);
         $this->allowAll();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::VISIBLE_STRING;
     }
diff --git a/lib/ASN1/UnknownConstructedObject.php b/lib/ASN1/UnknownConstructedObject.php
index b19a07a..9535d1c 100644
--- a/lib/ASN1/UnknownConstructedObject.php
+++ b/lib/ASN1/UnknownConstructedObject.php
@@ -7,13 +7,14 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
 class UnknownConstructedObject extends Construct
 {
-    private $identifier;
-    private $contentLength;
+    private string $identifier;
+    private int $contentLength;
 
     /**
      * @param string $binaryData
@@ -21,7 +22,7 @@ class UnknownConstructedObject extends Construct
      *
      * @throws \FG\ASN1\Exception\ParserException
      */
-    public function __construct($binaryData, &$offsetIndex)
+    public function __construct(string $binaryData, int &$offsetIndex)
     {
         $this->identifier = self::parseBinaryIdentifier($binaryData, $offsetIndex);
         $this->contentLength = self::parseContentLength($binaryData, $offsetIndex);
@@ -37,22 +38,22 @@ public function __construct($binaryData, &$offsetIndex)
         parent::__construct(...$children);
     }
 
-    public function getType()
+    public function getType(): int
     {
         return ord($this->identifier);
     }
 
-    public function getIdentifier()
+    public function getIdentifier(): string
     {
         return $this->identifier;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return $this->contentLength;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         return '';
     }
diff --git a/lib/ASN1/UnknownObject.php b/lib/ASN1/UnknownObject.php
index 4ac536a..2ebde31 100644
--- a/lib/ASN1/UnknownObject.php
+++ b/lib/ASN1/UnknownObject.php
@@ -7,21 +7,19 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\ASN1;
 
 class UnknownObject extends ASNObject
 {
-    /** @var string */
-    private $value;
-
-    private $identifier;
+    private string $value;
+    private string $identifier;
 
     /**
      * @param string|int $identifier Either the first identifier octet as int or all identifier bytes as a string
-     * @param int        $contentLength
      */
-    public function __construct($identifier, $contentLength)
+    public function __construct(string|int $identifier, int $contentLength)
     {
         if (is_int($identifier)) {
             $identifier = chr($identifier);
@@ -32,27 +30,27 @@ public function __construct($identifier, $contentLength)
         $this->setContentLength($contentLength);
     }
 
-    public function getContent()
+    public function getContent(): string
     {
         return $this->value;
     }
 
-    public function getType()
+    public function getType(): int
     {
         return ord($this->identifier[0]);
     }
 
-    public function getIdentifier()
+    public function getIdentifier(): string
     {
         return $this->identifier;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return $this->getContentLength();
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): ?string
     {
         return '';
     }
diff --git a/lib/Utility/BigInteger.php b/lib/Utility/BigInteger.php
index 866162c..dafa70b 100644
--- a/lib/Utility/BigInteger.php
+++ b/lib/Utility/BigInteger.php
@@ -5,6 +5,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\Utility;
 
@@ -22,34 +23,26 @@ abstract class BigInteger
 {
     /**
      * Force a preference on the underlying big number implementation, useful for testing.
-     * @var string|null
      */
-    private static $_prefer;
+    private static string|int|null $_prefer = null;
 
-    public static function setPrefer($prefer = null)
+    public static function setPrefer(string|int $prefer = null)
     {
         self::$_prefer = $prefer;
     }
 
     /**
      * Create a BigInteger instance based off the base 10 string or an integer.
-     * @param string|int $val
-     * @return BigInteger
      * @throws \InvalidArgumentException
      */
-    public static function create($val)
+    public static function create(string|int $val): BigInteger
     {
         if (self::$_prefer) {
-            switch (self::$_prefer) {
-                case 'gmp':
-                    $ret = new BigIntegerGmp();
-                    break;
-                case 'bcmath':
-                    $ret = new BigIntegerBcmath();
-                    break;
-                default:
-                    throw new \UnexpectedValueException('Unknown number implementation: ' . self::$_prefer);
-            }
+            $ret = match (self::$_prefer) {
+                'gmp' => new BigIntegerGmp(),
+                'bcmath' => new BigIntegerBcmath(),
+                default => throw new \UnexpectedValueException('Unknown number implementation: ' . self::$_prefer),
+            };
         }
         else {
             // autodetect
@@ -91,105 +84,80 @@ protected function __construct()
 
     /**
      * Subclasses must provide clone functionality.
-     * @return BigInteger
      */
-    abstract public function __clone();
+    abstract public function __clone(): void;
 
     /**
      * Assign the instance value from base 10 string.
-     * @param string $str
      */
-    abstract protected function _fromString($str);
+    abstract protected function _fromString(string $str): void;
 
     /**
      * Assign the instance value from an integer type.
-     * @param int $integer
      */
-    abstract protected function _fromInteger($integer);
+    abstract protected function _fromInteger(int $integer): void;
 
     /**
      * Must provide string implementation that returns base 10 number.
-     * @return string
      */
-    abstract public function __toString();
+    abstract public function __toString(): string;
 
     /* INFORMATIONAL FUNCTIONS */
 
     /**
      * Return integer, if possible. Throws an exception if the number can not be represented as a native integer.
-     * @return int
      * @throws \OverflowException
      */
-    abstract public function toInteger();
+    abstract public function toInteger(): int;
 
     /**
      * Is represented integer negative?
-     * @return bool
      */
-    abstract public function isNegative();
+    abstract public function isNegative(): bool;
 
     /**
      * Compare the integer with $number, returns a negative integer if $this is less than number, returns 0 if $this is
      * equal to number and returns a positive integer if $this is greater than number.
-     * @param BigInteger|string|int $number
-     * @return int
      */
-    abstract public function compare($number);
-
-    /* MODIFY */
+    abstract public function compare(BigInteger|string|int $number): int;
 
     /**
      * Add another integer $b and returns the result.
-     * @param BigInteger|string|int $b
-     * @return BigInteger
      */
-    abstract public function add($b);
+    abstract public function add(BigInteger|string|int $b): BigInteger;
 
     /**
      * Subtract $b from $this and returns the result.
-     * @param BigInteger|string|int $b
-     * @return BigInteger
      */
-    abstract public function subtract($b);
+    abstract public function subtract(BigInteger|string|int $b): BigInteger;
 
     /**
      * Multiply value.
-     * @param BigInteger|string|int $b
-     * @return BigInteger
      */
-    abstract public function multiply($b);
+    abstract public function multiply(BigInteger|string|int $b): BigInteger;
 
     /**
      * The value $this modulus $b.
-     * @param BigInteger|string|int $b
-     * @return BigInteger
      */
-    abstract public function modulus($b);
+    abstract public function modulus(BigInteger|string|int $b): BigInteger;
 
     /**
      * Raise $this to the power of $b and returns the result.
-     * @param BigInteger|string|int $b
-     * @return BigInteger
      */
-    abstract public function toPower($b);
+    abstract public function toPower(BigInteger|string|int $b): BigInteger;
 
     /**
      * Shift the value to the right by a set number of bits and returns the result.
-     * @param int $bits
-     * @return BigInteger
      */
-    abstract public function shiftRight($bits = 8);
+    abstract public function shiftRight(int $bits = 8): BigInteger;
 
     /**
      * Shift the value to the left by a set number of bits and returns the result.
-     * @param int $bits
-     * @return BigInteger
      */
-    abstract public function shiftLeft($bits = 8);
+    abstract public function shiftLeft(int $bits = 8): BigInteger;
 
     /**
      * Returns the absolute value.
-     * @return BigInteger
      */
-    abstract public function absoluteValue();
+    abstract public function absoluteValue(): BigInteger;
 }
diff --git a/lib/Utility/BigIntegerBcmath.php b/lib/Utility/BigIntegerBcmath.php
index 25ad891..866a6cc 100644
--- a/lib/Utility/BigIntegerBcmath.php
+++ b/lib/Utility/BigIntegerBcmath.php
@@ -5,6 +5,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\Utility;
 
@@ -16,29 +17,28 @@
  */
 class BigIntegerBcmath extends BigInteger
 {
-    protected $_str;
+    protected string $_str;
 
-    public function __clone()
+    public function __clone(): void
     {
-        // nothing needed to copy
     }
 
-    protected function _fromString($str)
+    protected function _fromString(string $str): void
     {
-        $this->_str = (string)$str;
+        $this->_str = $str;
     }
 
-    protected function _fromInteger($integer)
+    protected function _fromInteger(int $integer): void
     {
         $this->_str = (string)$integer;
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return $this->_str;
     }
 
-    public function toInteger()
+    public function toInteger(): int
     {
         if ($this->compare(PHP_INT_MAX) > 0 || $this->compare(PHP_INT_MIN) < 0) {
             throw new \OverflowException(sprintf('Can not represent %s as integer.', $this->_str));
@@ -46,46 +46,47 @@ public function toInteger()
         return (int)$this->_str;
     }
 
-    public function isNegative()
+    public function isNegative(): bool
     {
         return bccomp($this->_str, '0', 0) < 0;
     }
 
-    protected function _unwrap($number)
+    protected function _unwrap(BigInteger|string|int $number): string
     {
         if ($number instanceof self) {
             return $number->_str;
         }
-        return $number;
+
+        return (string)$number;
     }
 
-    public function compare($number)
+    public function compare(BigInteger|string|int $number): int
     {
         return bccomp($this->_str, $this->_unwrap($number), 0);
     }
 
-    public function add($b)
+    public function add(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_str = bcadd($this->_str, $this->_unwrap($b), 0);
         return $ret;
     }
 
-    public function subtract($b)
+    public function subtract(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_str = bcsub($this->_str, $this->_unwrap($b), 0);
         return $ret;
     }
 
-    public function multiply($b)
+    public function multiply(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_str = bcmul($this->_str, $this->_unwrap($b), 0);
         return $ret;
     }
 
-    public function modulus($b)
+    public function modulus(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         if ($this->isNegative()) {
@@ -99,27 +100,28 @@ public function modulus($b)
         return $ret;
     }
 
-    public function toPower($b)
+    public function toPower(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_str = bcpow($this->_str, $this->_unwrap($b), 0);
         return $ret;
     }
 
-    public function shiftRight($bits = 8)
+    public function shiftRight(int $bits = 8): BigInteger
     {
         $ret = new self();
-        $ret->_str = bcdiv($this->_str, bcpow('2', $bits));
+        $ret->_str = bcdiv($this->_str, bcpow('2', (string)$bits));
         return $ret;
     }
 
-    public function shiftLeft($bits = 8) {
+    public function shiftLeft(int $bits = 8): BigInteger
+    {
         $ret = new self();
-        $ret->_str = bcmul($this->_str, bcpow('2', $bits));
+        $ret->_str = bcmul($this->_str, bcpow('2', (string)$bits));
         return $ret;
     }
 
-    public function absoluteValue()
+    public function absoluteValue(): BigInteger
     {
         $ret = new self();
         if (-1 === bccomp($this->_str, '0', 0)) {
diff --git a/lib/Utility/BigIntegerGmp.php b/lib/Utility/BigIntegerGmp.php
index 0791226..9304269 100644
--- a/lib/Utility/BigIntegerGmp.php
+++ b/lib/Utility/BigIntegerGmp.php
@@ -5,9 +5,12 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\Utility;
 
+use GMP;
+
 /**
  * Class BigIntegerGmp
  * Integer representation of big numbers using the GMP extension to perform operations.
@@ -16,33 +19,29 @@
  */
 class BigIntegerGmp extends BigInteger
 {
-    /**
-     * Resource handle.
-     * @var \GMP
-     */
-    protected $_rh;
+    protected GMP $_rh;
 
-    public function __clone()
+    public function __clone(): void
     {
         $this->_rh = gmp_add($this->_rh, 0);
     }
 
-    protected function _fromString($str)
+    protected function _fromString($str): void
     {
         $this->_rh = gmp_init($str, 10);
     }
 
-    protected function _fromInteger($integer)
+    protected function _fromInteger($integer): void
     {
         $this->_rh = gmp_init($integer, 10);
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         return gmp_strval($this->_rh, 10);
     }
 
-    public function toInteger()
+    public function toInteger(): int
     {
         if ($this->compare(PHP_INT_MAX) > 0 || $this->compare(PHP_INT_MIN) < 0) {
             throw new \OverflowException(sprintf('Can not represent %s as integer.', $this));
@@ -50,12 +49,12 @@ public function toInteger()
         return gmp_intval($this->_rh);
     }
 
-    public function isNegative()
+    public function isNegative(): bool
     {
         return gmp_sign($this->_rh) === -1;
     }
 
-    protected function _unwrap($number)
+    protected function _unwrap(BigInteger|string|int $number): BigInteger|GMP|string|int
     {
         if ($number instanceof self) {
             return $number->_rh;
@@ -63,40 +62,40 @@ protected function _unwrap($number)
         return $number;
     }
 
-    public function compare($number)
+    public function compare(BigInteger|string|int $number): int
     {
         return gmp_cmp($this->_rh, $this->_unwrap($number));
     }
 
-    public function add($b)
+    public function add(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_rh = gmp_add($this->_rh, $this->_unwrap($b));
         return $ret;
     }
 
-    public function subtract($b)
+    public function subtract(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_rh = gmp_sub($this->_rh, $this->_unwrap($b));
         return $ret;
     }
 
-    public function multiply($b)
+    public function multiply(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_rh = gmp_mul($this->_rh, $this->_unwrap($b));
         return $ret;
     }
 
-    public function modulus($b)
+    public function modulus(BigInteger|string|int $b): BigInteger
     {
         $ret = new self();
         $ret->_rh = gmp_mod($this->_rh, $this->_unwrap($b));
         return $ret;
     }
 
-    public function toPower($b)
+    public function toPower(BigInteger|string|int $b): BigInteger
     {
         if ($b instanceof self) {
             // gmp_pow accepts just an integer
@@ -110,21 +109,21 @@ public function toPower($b)
         return $ret;
     }
 
-    public function shiftRight($bits=8)
+    public function shiftRight(int $bits = 8): BigInteger
     {
         $ret = new self();
         $ret->_rh = gmp_div($this->_rh, gmp_pow(2, $bits));
         return $ret;
     }
 
-    public function shiftLeft($bits=8)
+    public function shiftLeft(int $bits = 8): BigInteger
     {
         $ret = new self();
         $ret->_rh = gmp_mul($this->_rh, gmp_pow(2, $bits));
         return $ret;
     }
 
-    public function absoluteValue()
+    public function absoluteValue(): BigInteger
     {
         $ret = new self();
         $ret->_rh = gmp_abs($this->_rh);
diff --git a/lib/X509/AlgorithmIdentifier.php b/lib/X509/AlgorithmIdentifier.php
index a06b56f..fdc77d7 100644
--- a/lib/X509/AlgorithmIdentifier.php
+++ b/lib/X509/AlgorithmIdentifier.php
@@ -7,15 +7,17 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509;
 
 use FG\ASN1\Universal\NullObject;
 use FG\ASN1\Composite\AttributeTypeAndValue;
+use FG\ASN1\Universal\ObjectIdentifier;
 
 class AlgorithmIdentifier extends AttributeTypeAndValue
 {
-    public function __construct($objectIdentifierString)
+    public function __construct(ObjectIdentifier|string $objectIdentifierString)
     {
         parent::__construct($objectIdentifierString, new NullObject());
     }
diff --git a/lib/X509/CSR/Attributes.php b/lib/X509/CSR/Attributes.php
index 5a965e2..5a13525 100644
--- a/lib/X509/CSR/Attributes.php
+++ b/lib/X509/CSR/Attributes.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509\CSR;
 
@@ -22,12 +23,12 @@
 
 class Attributes extends Construct implements Parsable
 {
-    public function getType()
+    public function getType(): int
     {
         return 0xA0;
     }
 
-    public function addAttribute($objectIdentifier, Set $attribute)
+    public function addAttribute($objectIdentifier, Set $attribute): void
     {
         if (is_string($objectIdentifier)) {
             $objectIdentifier = new ObjectIdentifier($objectIdentifier);
@@ -37,7 +38,7 @@ public function addAttribute($objectIdentifier, Set $attribute)
         $this->addChild($attributeSequence);
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], 0xA0, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex);
diff --git a/lib/X509/CSR/CSR.php b/lib/X509/CSR/CSR.php
index 8f2a319..abc5078 100644
--- a/lib/X509/CSR/CSR.php
+++ b/lib/X509/CSR/CSR.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509\CSR;
 
@@ -21,28 +22,20 @@
 class CSR extends Sequence
 {
     const CSR_VERSION_NR = 0;
-
-    protected $subject;
-    protected $publicKey;
-    protected $signature;
-    protected $signatureAlgorithm;
-
-    protected $startSequence;
-
-    /**
-     * @param string $commonName
-     * @param string $email
-     * @param string $organization
-     * @param string $locality
-     * @param string $state
-     * @param string $country
-     * @param string $organizationalUnit
-     * @param string $publicKey
-     * @param string $signature
-     * @param string $signatureAlgorithm
-     */
-    public function __construct($commonName, $email, $organization, $locality, $state, $country, $organizationalUnit, $publicKey, $signature = null, $signatureAlgorithm = OID::SHA1_WITH_RSA_SIGNATURE)
-    {
+    private CertificateSubject $subject;
+
+    public function __construct(
+        string $commonName,
+        string $email,
+        string $organization,
+        string $locality,
+        string $state,
+        string $country,
+        string $organizationalUnit,
+        private string $publicKey,
+        private ?string $signature = null,
+        private string $signatureAlgorithm = OID::SHA1_WITH_RSA_SIGNATURE
+    ) {
         $this->subject = new CertificateSubject(
             $commonName,
             $email,
@@ -52,16 +45,15 @@ public function __construct($commonName, $email, $organization, $locality, $stat
             $country,
             $organizationalUnit
         );
-        $this->publicKey = $publicKey;
-        $this->signature = $signature;
-        $this->signatureAlgorithm = $signatureAlgorithm;
 
-        if (isset($signature)) {
+        if ($signature !== null) {
             $this->createCSRSequence();
         }
+
+        parent::__construct();
     }
 
-    protected function createCSRSequence()
+    protected function createCSRSequence(): void
     {
         $versionNr            = new Integer(self::CSR_VERSION_NR);
         $publicKey            = new PublicKey($this->publicKey);
@@ -78,7 +70,7 @@ protected function createCSRSequence()
         $this->addChild($signature);
     }
 
-    public function getSignatureSubject()
+    public function getSignatureSubject(): string
     {
         $versionNr            = new Integer(self::CSR_VERSION_NR);
         $publicKey            = new PublicKey($this->publicKey);
@@ -87,7 +79,7 @@ public function getSignatureSubject()
         return $certRequestInfo->getBinary();
     }
 
-    public function setSignature($signature, $signatureAlgorithm = OID::SHA1_WITH_RSA_SIGNATURE)
+    public function setSignature($signature, $signatureAlgorithm = OID::SHA1_WITH_RSA_SIGNATURE): void
     {
         $this->signature = $signature;
         $this->signatureAlgorithm = $signatureAlgorithm;
@@ -95,7 +87,7 @@ public function setSignature($signature, $signatureAlgorithm = OID::SHA1_WITH_RS
         $this->createCSRSequence();
     }
 
-    public function __toString()
+    public function __toString(): string
     {
         $tmp = base64_encode($this->getBinary());
 
@@ -112,47 +104,47 @@ public function __toString()
         return $result;
     }
 
-    public function getVersion()
+    public function getVersion(): int
     {
         return self::CSR_VERSION_NR;
     }
 
-    public function getOrganizationName()
+    public function getOrganizationName(): string
     {
         return $this->subject->getOrganization();
     }
 
-    public function getLocalName()
+    public function getLocalName(): string
     {
         return $this->subject->getLocality();
     }
 
-    public function getState()
+    public function getState(): string
     {
         return $this->subject->getState();
     }
 
-    public function getCountry()
+    public function getCountry(): string
     {
         return $this->subject->getCountry();
     }
 
-    public function getOrganizationalUnit()
+    public function getOrganizationalUnit(): string
     {
         return $this->subject->getOrganizationalUnit();
     }
 
-    public function getPublicKey()
+    public function getPublicKey(): string
     {
         return $this->publicKey;
     }
 
-    public function getSignature()
+    public function getSignature(): string
     {
         return $this->signature;
     }
 
-    public function getSignatureAlgorithm()
+    public function getSignatureAlgorithm(): string
     {
         return $this->signatureAlgorithm;
     }
diff --git a/lib/X509/CertificateExtensions.php b/lib/X509/CertificateExtensions.php
index 6ed1c6a..2a1220f 100644
--- a/lib/X509/CertificateExtensions.php
+++ b/lib/X509/CertificateExtensions.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509;
 
@@ -23,8 +24,8 @@
 
 class CertificateExtensions extends Set implements Parsable
 {
-    private $innerSequence;
-    private $extensions = [];
+    private Sequence $innerSequence;
+    private array $extensions = [];
 
     public function __construct()
     {
@@ -32,12 +33,12 @@ public function __construct()
         parent::__construct($this->innerSequence);
     }
 
-    public function addSubjectAlternativeNames(SubjectAlternativeNames $sans)
+    public function addSubjectAlternativeNames(SubjectAlternativeNames $sans): void
     {
         $this->addExtension(OID::CERT_EXT_SUBJECT_ALT_NAME, $sans);
     }
 
-    private function addExtension($oidString, ASNObject $extension)
+    private function addExtension(string $oidString, ASNObject $extension): void
     {
         $sequence = new Sequence();
         $sequence->addChild(new ObjectIdentifier($oidString));
@@ -47,12 +48,12 @@ private function addExtension($oidString, ASNObject $extension)
         $this->extensions[] = $extension;
     }
 
-    public function getContent()
+    public function getContent(): array
     {
         return $this->extensions;
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::SET, $offsetIndex++);
         self::parseContentLength($binaryData, $offsetIndex);
diff --git a/lib/X509/CertificateSubject.php b/lib/X509/CertificateSubject.php
index 0a04d57..958902b 100644
--- a/lib/X509/CertificateSubject.php
+++ b/lib/X509/CertificateSubject.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509;
 
@@ -19,25 +20,15 @@
 
 class CertificateSubject extends Sequence implements Parsable
 {
-    private $commonName;
-    private $email;
-    private $organization;
-    private $locality;
-    private $state;
-    private $country;
-    private $organizationalUnit;
-
-    /**
-     * @param string $commonName
-     * @param string $email
-     * @param string $organization
-     * @param string $locality
-     * @param string $state
-     * @param string $country
-     * @param string $organizationalUnit
-     */
-    public function __construct($commonName, $email, $organization, $locality, $state, $country, $organizationalUnit)
-    {
+    public function __construct(
+        private string $commonName,
+        private string $email,
+        private string $organization,
+        private string $locality,
+        private string $state,
+        private string $country,
+        private string $organizationalUnit
+    ) {
         parent::__construct(
             new RDNString(OID::COUNTRY_NAME, $country),
             new RDNString(OID::STATE_OR_PROVINCE_NAME, $state),
@@ -47,52 +38,44 @@ public function __construct($commonName, $email, $organization, $locality, $stat
             new RDNString(OID::COMMON_NAME, $commonName),
             new RDNString(OID::PKCS9_EMAIL, $email)
         );
-
-        $this->commonName = $commonName;
-        $this->email = $email;
-        $this->organization = $organization;
-        $this->locality = $locality;
-        $this->state = $state;
-        $this->country = $country;
-        $this->organizationalUnit = $organizationalUnit;
     }
 
-    public function getCommonName()
+    public function getCommonName(): string
     {
         return $this->commonName;
     }
 
-    public function getEmail()
+    public function getEmail(): string
     {
         return $this->email;
     }
 
-    public function getOrganization()
+    public function getOrganization(): string
     {
         return $this->organization;
     }
 
-    public function getLocality()
+    public function getLocality(): string
     {
         return $this->locality;
     }
 
-    public function getState()
+    public function getState(): string
     {
         return $this->state;
     }
 
-    public function getCountry()
+    public function getCountry(): string
     {
         return $this->country;
     }
 
-    public function getOrganizationalUnit()
+    public function getOrganizationalUnit(): string
     {
         return $this->organizationalUnit;
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::SEQUENCE, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex);
diff --git a/lib/X509/PrivateKey.php b/lib/X509/PrivateKey.php
index d57ad86..76d852a 100644
--- a/lib/X509/PrivateKey.php
+++ b/lib/X509/PrivateKey.php
@@ -7,9 +7,11 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509;
 
+use FG\ASN1\ASNObject;
 use FG\ASN1\OID;
 use FG\ASN1\Universal\NullObject;
 use FG\ASN1\Universal\Sequence;
@@ -18,11 +20,7 @@
 
 class PrivateKey extends Sequence
 {
-    /**
-     * @param string $hexKey
-     * @param \FG\ASN1\ASNObject|string $algorithmIdentifierString
-     */
-    public function __construct($hexKey, $algorithmIdentifierString = OID::RSA_ENCRYPTION)
+    public function __construct(string $hexKey, ASNObject|string $algorithmIdentifierString = OID::RSA_ENCRYPTION)
     {
         parent::__construct(
             new Sequence(
diff --git a/lib/X509/PublicKey.php b/lib/X509/PublicKey.php
index ab8b451..eb420d8 100644
--- a/lib/X509/PublicKey.php
+++ b/lib/X509/PublicKey.php
@@ -7,9 +7,11 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509;
 
+use FG\ASN1\ASNObject;
 use FG\ASN1\OID;
 use FG\ASN1\Universal\NullObject;
 use FG\ASN1\Universal\Sequence;
@@ -18,11 +20,7 @@
 
 class PublicKey extends Sequence
 {
-    /**
-     * @param string $hexKey
-     * @param \FG\ASN1\ASNObject|string $algorithmIdentifierString
-     */
-    public function __construct($hexKey, $algorithmIdentifierString = OID::RSA_ENCRYPTION)
+    public function __construct(string $hexKey, ASNObject|string $algorithmIdentifierString = OID::RSA_ENCRYPTION)
     {
         parent::__construct(
             new Sequence(
diff --git a/lib/X509/SAN/DNSName.php b/lib/X509/SAN/DNSName.php
index 502738b..f39f66f 100644
--- a/lib/X509/SAN/DNSName.php
+++ b/lib/X509/SAN/DNSName.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509\SAN;
 
@@ -16,12 +17,12 @@ class DNSName extends GeneralString
 {
     const IDENTIFIER = 0x82; // not sure yet why this is the identifier used in SAN extensions
 
-    public function __construct($dnsNameString)
+    public function __construct(string $dnsNameString)
     {
         parent::__construct($dnsNameString);
     }
 
-    public function getType()
+    public function getType(): int
     {
         return self::IDENTIFIER;
     }
diff --git a/lib/X509/SAN/IPAddress.php b/lib/X509/SAN/IPAddress.php
index f55be95..82ccca1 100644
--- a/lib/X509/SAN/IPAddress.php
+++ b/lib/X509/SAN/IPAddress.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509\SAN;
 
@@ -18,41 +19,37 @@ class IPAddress extends ASNObject implements Parsable
 {
     const IDENTIFIER = 0x87; // not sure yet why this is the identifier used in SAN extensions
 
-    /** @var string */
-    private $value;
-
-    public function __construct($ipAddressString)
+    public function __construct(private string $value)
     {
-        $this->value = $ipAddressString;
     }
 
-    public function getType()
+    public function getType(): int
     {
         return self::IDENTIFIER;
     }
 
-    public function getContent()
+    public function getContent(): string
     {
         return $this->value;
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return 4;
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): string
     {
         $ipParts = explode('.', $this->value);
-        $binary  = chr($ipParts[0]);
-        $binary .= chr($ipParts[1]);
-        $binary .= chr($ipParts[2]);
-        $binary .= chr($ipParts[3]);
+        $binary  = chr((int)$ipParts[0]);
+        $binary .= chr((int)$ipParts[1]);
+        $binary .= chr((int)$ipParts[2]);
+        $binary .= chr((int)$ipParts[3]);
 
         return $binary;
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], self::IDENTIFIER, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex);
diff --git a/lib/X509/SAN/SubjectAlternativeNames.php b/lib/X509/SAN/SubjectAlternativeNames.php
index 271ddde..b02bd96 100644
--- a/lib/X509/SAN/SubjectAlternativeNames.php
+++ b/lib/X509/SAN/SubjectAlternativeNames.php
@@ -7,6 +7,7 @@
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
  */
+declare(strict_types=1);
 
 namespace FG\X509\SAN;
 
@@ -22,44 +23,44 @@
  */
 class SubjectAlternativeNames extends ASNObject implements Parsable
 {
-    private $alternativeNamesSequence;
+    private Sequence $alternativeNamesSequence;
 
     public function __construct()
     {
         $this->alternativeNamesSequence = new Sequence();
     }
 
-    protected function calculateContentLength()
+    protected function calculateContentLength(): int
     {
         return $this->alternativeNamesSequence->getObjectLength();
     }
 
-    public function getType()
+    public function getType(): int
     {
         return Identifier::OCTETSTRING;
     }
 
-    public function addDomainName(DNSName $domainName)
+    public function addDomainName(DNSName $domainName): void
     {
         $this->alternativeNamesSequence->addChild($domainName);
     }
 
-    public function addIP(IPAddress $ip)
+    public function addIP(IPAddress $ip): void
     {
         $this->alternativeNamesSequence->addChild($ip);
     }
 
-    public function getContent()
+    public function getContent(): array
     {
         return $this->alternativeNamesSequence->getContent();
     }
 
-    protected function getEncodedValue()
+    protected function getEncodedValue(): string
     {
         return $this->alternativeNamesSequence->getBinary();
     }
 
-    public static function fromBinary(&$binaryData, &$offsetIndex = 0)
+    public static function fromBinary(string &$binaryData, ?int &$offsetIndex = 0): static
     {
         self::parseIdentifier($binaryData[$offsetIndex], Identifier::OCTETSTRING, $offsetIndex++);
         $contentLength = self::parseContentLength($binaryData, $offsetIndex);