crypto.go

package gothic

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"io"
)

func Encrypt(stringToEncrypt string, keyString string) (encryptedString string) {
	//Since the key is in string, we need to convert decode it to bytes
	key, _ := hex.DecodeString(keyString)
	plaintext := []byte(stringToEncrypt)
	//Create a new Cipher Block from the key
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err.Error())
	}
	//Create a new GCM - https://en.wikipedia.org/wiki/Galois/Counter_Mode
	//https://golang.org/pkg/crypto/cipher/#NewGCM
	aesGCM, err := cipher.NewGCM(block)
	if err != nil {
		panic(err.Error())
	}
	//Create a nonce. Nonce should be from GCM
	nonce := make([]byte, aesGCM.NonceSize())
	if _, err = io.ReadFull(rand.Reader, nonce); err != nil {
		panic(err.Error())
	}
	//Encrypt the data using aesGCM.Seal
	//Since we don't want to save the nonce somewhere else in this case, we add it as a prefix to the encrypted data. The first nonce argument in Seal is the prefix.
	ciphertext := aesGCM.Seal(nonce, nonce, plaintext, nil)
	return fmt.Sprintf("%x", ciphertext)
}

func Decrypt(encryptedString string, keyString string) (decryptedString string) {
	key, _ := hex.DecodeString(keyString)
	enc, _ := hex.DecodeString(encryptedString)
	//Create a new Cipher Block from the key
	block, err := aes.NewCipher(key)
	if err != nil {
		panic(err.Error())
	}
	//Create a new GCM
	aesGCM, err := cipher.NewGCM(block)
	if err != nil {
		panic(err.Error())
	}
	//Get the nonce size
	nonceSize := aesGCM.NonceSize()
	//Extract the nonce from the encrypted data
	nonce, ciphertext := enc[:nonceSize], enc[nonceSize:]
	//Decrypt the data
	plaintext, err := aesGCM.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		panic(err.Error())
	}
	return fmt.Sprintf("%s", plaintext)
}

// GenerateRandomBytes returns securely generated random bytes.
// It will return an error if the system's secure random
// number generator fails to function correctly, in which
// case the caller should not continue.
func GenerateRandomBytes(n int) ([]byte, error) {
	b := make([]byte, n)
	_, err := rand.Read(b)
	// Note that err == nil only if we read len(b) bytes.
	if err != nil {
		return nil, err
	}

	return b, nil
}

// GenerateRandomString returns a securely generated random string.
// It will return an error if the system's secure random
// number generator fails to function correctly, in which
// case the caller should not continue.
func GenerateRandomString(n int) (string, error) {
	const letters = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-"
	bytes, err := GenerateRandomBytes(n)
	if err != nil {
		return "", err
	}
	for i, b := range bytes {
		bytes[i] = letters[b%byte(len(letters))]
	}
	return string(bytes), nil
}

func MakeKeyString() (string, error) {
	bytes := make([]byte, 32) //generate a random 32 byte key for AES-256
	if _, err := rand.Read(bytes); err != nil {
		return "", err
	}
	return hex.EncodeToString(bytes), nil
}