base58.php

<?php
class Base58
{
    /***
     * encode a hexadecimal string in Base58.
     *
     * @param string $data (hexa)
     * @param bool $littleEndian
     * @return string (base58)
     * @throws \Exception
     */
    static public function encode($data, $littleEndian = true): string
    {
        $res = '';
        $dataIntVal = gmp_init($data, 16);
        while (gmp_cmp($dataIntVal, gmp_init(0, 10)) > 0) {
            $qr = gmp_div_qr($dataIntVal, gmp_init(58, 10));
            $dataIntVal = $qr[0];
            $reminder = gmp_strval($qr[1]);
            if (!Base58::permutation($reminder)) {
                throw new \Exception('Something went wrong during base58 encoding');
            }
            $res .= Base58::permutation($reminder);
        }

        //get number of leading zeros
        $leading = '';
        $i = 0;
        while (substr($data, $i, 1) === '0') {
            if ($i !== 0 && $i % 2) {
                $leading .= '1';
            }
            $i++;
        }

        if ($littleEndian)
            return strrev($res . $leading);
        else
            return $res . $leading;
    }

    /***
     * Decode a Base58 encoded string and returns it's value as a hexadecimal string
     *
     * @param string $encodedData (base58)
     * @param bool $littleEndian
     * @return string (hexa)
     */
    static public function decode($encodedData, $littleEndian = true): string
    {
        $res = gmp_init(0, 10);
        $length = strlen($encodedData);
        if ($littleEndian) {
            $encodedData = strrev($encodedData);
        }

        for ($i = $length - 1; $i >= 0; $i--) {
            $res = gmp_add(
                gmp_mul(
                    $res,
                    gmp_init(58, 10)
                ),
                Base58::permutation(substr($encodedData, $i, 1), true)
            );
        }

        $res = gmp_strval($res, 16);
        $i = $length - 1;
        while (substr($encodedData, $i, 1) === '1') {
            $res = '00' . $res;
            $i--;
        }

        if (strlen($res) % 2 !== 0) {
            $res = '0' . $res;
        }

        return $res;
    }

    /***
     * Permutation table used for Base58 encoding and decoding.
     *
     * @param string $char
     * @param bool $reverse
     * @return string|null
     */
    static public function permutation($char, $reverse = false): string
    {
        $table = ['1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'];

        if ($reverse) {
            $reversedTable = [];
            foreach ($table as $key => $element) {
                $reversedTable[$element] = $key;
            }

            if (isset($reversedTable[$char]))
                return $reversedTable[$char];
            else
                return null;
        }

        if (isset($table[$char]))
            return $table[$char];
        else
            return null;
    }
}