crypt.go

package cryptanalysis

import (
	"crypto/aes"
	"errors"
)

const block_size = 16

func EncryptXor(plain, key []byte) []byte {
	var cipher []byte

	for i := 0; i < len(plain); i++ {
		e := plain[i] ^ key[i%len(key)]
		cipher = append(cipher, e)
	}

	return cipher
}

func EncryptEcb(plaintext, key []byte) ([]byte, error) {
	ciphertext := make([]byte, 0)
	plaintext = PadPkcs7(plaintext, block_size)
	chunks := Chunk(plaintext, block_size)

	ecb, err := aes.NewCipher(key)
	if err != nil {
		return ciphertext, err
	}

	for _, chunk := range chunks {
		temp := make([]byte, block_size)

		ecb.Encrypt(temp, chunk)

		ciphertext = append(ciphertext, temp...)
	}

	return ciphertext, nil
}

func DecryptEcb(ciphertext, key []byte) ([]byte, error) {
	plaintext := make([]byte, 0)

	if len(ciphertext)%block_size != 0 {
		return plaintext, errors.New("Ciphertext is not padded properly.")
	}

	chunks := Chunk(ciphertext, block_size)
	ecb, err := aes.NewCipher(key)
	if err != nil {
		return plaintext, err
	}

	for _, chunk := range chunks {
		temp := make([]byte, block_size)

		ecb.Decrypt(temp, chunk)

		plaintext = append(plaintext, temp...)
	}

	return plaintext, nil
}

func EncryptCbc(plaintext, key, iv []byte) ([]byte, error) {
	null := make([]byte, 0)
	ciphertext := make([]byte, 0)
	plaintext = PadPkcs7(plaintext, block_size)

	if len(iv) != block_size {
		return null, errors.New("IV must be 16 bytes long.")
	}

	cbc, err := aes.NewCipher(key)
	if err != nil {
		return null, err
	}

	chunks := Chunk(plaintext, block_size)
	for _, chunk := range chunks {
		temp := make([]byte, block_size)

		chunk, err = XorArrays(chunk, iv)
		if err != nil {
			return null, err
		}

		cbc.Encrypt(temp, chunk)
		iv = temp

		ciphertext = append(ciphertext, temp...)
	}

	return ciphertext, nil
}

func DecryptCbc(ciphertext, key, iv []byte) ([]byte, error) {
	null := make([]byte, 0)
	plaintext := make([]byte, 0)

	if len(iv) != block_size {
		return null, errors.New("IV must be 16 bytes long.")
	}

	cbc, err := aes.NewCipher(key)
	if err != nil {
		return null, err
	}

	chunks := Chunk(ciphertext, block_size)
	for _, chunk := range chunks {
		temp := make([]byte, block_size)

		cbc.Decrypt(temp, chunk)
		temp, err = XorArrays(temp, iv)
		if err != nil {
			return null, err
		}
		iv = chunk

		plaintext = append(plaintext, temp...)
	}

	return plaintext, nil
}