JWX\JWE\EncryptionAlgorithm\AESCBCAlgorithm

Complexity

Total Complexity

21

Size/Duplication

Total Lines	209
Duplicated Lines	0 %

Coupling/Cohesion

Components	1
Dependencies	2

Test Coverage

Coverage

95.16%

Importance

Changes

0

11 Methods

Rating	Name	Duplication	Size	Complexity
A	_computeAuthTag()	0	4	1
A	headerParameters()	0	3	1
A	encrypt()	0	14	2
A	_validateKey()	0	4	2
A	_validateIV()	0	5	2
A	decrypt()	0	16	3
A	_aadLen()	0	7	2
A	_macKey()	0	3	1
A	_getCipherMethod()	0	14	3
A	ivSize()	0	3	1
A	_encKey()	0	3	1

<?php

declare(strict_types = 1);

namespace Sop\JWX\JWE\EncryptionAlgorithm;

use Sop\JWX\JWE\ContentEncryptionAlgorithm;
use Sop\JWX\JWE\Exception\AuthenticationException;
use Sop\JWX\JWT\Parameter\EncryptionAlgorithmParameter;

/**
 * Base class for algorithms implementing AES in CBC mode with HMAC-SHA.
 *
 * @see https://tools.ietf.org/html/rfc7518#section-5.2
 */
abstract class AESCBCAlgorithm implements ContentEncryptionAlgorithm
{
    /**
     * {@inheritdoc}
     */
    public function encrypt(string $plaintext, string $key, string $iv,
        string $aad): array
    {
        $this->_validateKey($key);
        $this->_validateIV($iv);
        $ciphertext = openssl_encrypt($plaintext, $this->_getCipherMethod(),
            $this->_encKey($key), OPENSSL_RAW_DATA, $iv);
        if (false === $ciphertext) {
            throw new \RuntimeException(
                'openssl_encrypt() failed: ' . $this->_getLastOpenSSLError());
        }
        $auth_data = $aad . $iv . $ciphertext . $this->_aadLen($aad);
        $auth_tag = $this->_computeAuthTag($auth_data, $key);
        return [$ciphertext, $auth_tag];
    }

    /**
     * {@inheritdoc}
     */
    public function decrypt(string $ciphertext, string $key, string $iv,
        string $aad, string $auth_tag): string
    {
        $this->_validateKey($key);
        $this->_validateIV($iv);
        $auth_data = $aad . $iv . $ciphertext . $this->_aadLen($aad);
        if ($this->_computeAuthTag($auth_data, $key) !== $auth_tag) {
            throw new AuthenticationException('Message authentication failed.');
        }
        $plaintext = openssl_decrypt($ciphertext, $this->_getCipherMethod(),
            $this->_encKey($key), OPENSSL_RAW_DATA, $iv);
        if (false === $plaintext) {
            throw new \RuntimeException(
                'openssl_decrypt() failed: ' . $this->_getLastOpenSSLError());
        }
        return $plaintext;
    }

    /**
     * {@inheritdoc}
     */
    public function ivSize(): int
    {
        return 16;
    }

    /**
     * {@inheritdoc}
     */
    public function headerParameters(): array
    {
        return [EncryptionAlgorithmParameter::fromAlgorithm($this)];
    }

    /**
     * Get cipher method name that is recognized by OpenSSL.
     *
     * @return string
     */
    abstract protected function _cipherMethod(): string;

    /**
     * Get algorithm name that is recognized by the Hash extension.
     *
     * @return string
     */
    abstract protected function _hashAlgo(): string;

    /**
     * Get length of the encryption key.
     *
     * @return int
     */
    abstract protected function _encKeyLen(): int;

    /**
     * Get length of the MAC key.
     *
     * @return int
     */
    abstract protected function _macKeyLen(): int;

    /**
     * Get length of the authentication tag.
     *
     * @return int
     */
    abstract protected function _tagLen(): int;

    /**
     * Get cipher method and verify that it's supported.
     *
     * @throws \RuntimeException
     *
     * @return string
     */
    final protected function _getCipherMethod(): string
    {
        static $supported_ciphers;
        if (!isset($supported_ciphers)) {
            $supported_ciphers = array_flip(
                array_map('strtolower', openssl_get_cipher_methods(false)));
        }
        $method = $this->_cipherMethod();
        if (!isset($supported_ciphers[$method])) {
            throw new \RuntimeException(
                "Cipher method {$method} is not" .
                     ' supported by this version of OpenSSL.');
        }
        return $method;
    }

    /**
     * Check that key is valid.
     *
     * @param string $key
     *
     * @throws \RuntimeException
     */
    final protected function _validateKey(string $key): void
    {
        if (strlen($key) !== $this->keySize()) {
            throw new \RuntimeException('Invalid key size.');
        }
    }

    /**
     * Check that IV is valid.
     *
     * @param string $iv
     *
     * @throws \RuntimeException
     */
    final protected function _validateIV(string $iv): void
    {
        $len = openssl_cipher_iv_length($this->_getCipherMethod());
        if ($len !== strlen($iv)) {
            throw new \RuntimeException('Invalid IV length.');
        }
    }

    /**
     * Get MAC key from CEK.
     *
     * @param string $key
     *
     * @return string
     */
    final protected function _macKey(string $key): string
    {
        return substr($key, 0, $this->_macKeyLen());
    }

    /**
     * Get encryption key from CEK.
     *
     * @param string $key
     *
     * @return string
     */
    final protected function _encKey(string $key): string
    {
        return substr($key, -$this->_encKeyLen());
    }

    /**
     * Compute AL value.
     *
     * @param string $aad
     *
     * @return string 64 bits
     */
    final protected function _aadLen(string $aad): string
    {
        // truncate on 32 bit hosts
        if (PHP_INT_SIZE < 8) {
            return "\0\0\0\0" . pack('N', strlen($aad) * 8);
        }
        return pack('J', strlen($aad) * 8);
    }

    /**
     * Compute authentication tag.
     *
     * @param string $data
     * @param string $key  CEK
     *
     * @return string
     */
    final protected function _computeAuthTag(string $data, string $key): string
    {
        $tag = hash_hmac($this->_hashAlgo(), $data, $this->_macKey($key), true);
        return substr($tag, 0, $this->_tagLen());
    }

    /**
     * Get last OpenSSL error message.
     *
     * @return null|string
     */
    protected function _getLastOpenSSLError(): ?string
    {
        $msg = null;
        while (false !== ($err = openssl_error_string())) {
            $msg = $err;
        }
        return $msg;
    }
}