JWEDecrypter.php

<?php

declare(strict_types=1);

namespace Jose\Component\Encryption;

use function array_key_exists;
use InvalidArgumentException;
use function is_string;
use Jose\Component\Core\Algorithm;
use Jose\Component\Core\AlgorithmManager;
use Jose\Component\Core\JWK;
use Jose\Component\Core\JWKSet;
use Jose\Component\Core\Util\KeyChecker;
use Jose\Component\Encryption\Algorithm\ContentEncryptionAlgorithm;
use Jose\Component\Encryption\Algorithm\KeyEncryption\DirectEncryption;
use Jose\Component\Encryption\Algorithm\KeyEncryption\KeyAgreement;
use Jose\Component\Encryption\Algorithm\KeyEncryption\KeyAgreementWithKeyWrapping;
use Jose\Component\Encryption\Algorithm\KeyEncryption\KeyEncryption;
use Jose\Component\Encryption\Algorithm\KeyEncryption\KeyWrapping;
use Jose\Component\Encryption\Algorithm\KeyEncryptionAlgorithm;
use Jose\Component\Encryption\Compression\CompressionMethodManager;
use Throwable;

class JWEDecrypter
{
    public function __construct(
        private readonly AlgorithmManager $keyEncryptionAlgorithmManager,
        private readonly AlgorithmManager $contentEncryptionAlgorithmManager,
        private readonly CompressionMethodManager $compressionMethodManager
    ) {
    }

    /**
     * Returns the key encryption algorithm manager.
     */
    public function getKeyEncryptionAlgorithmManager(): AlgorithmManager
    {
        return $this->keyEncryptionAlgorithmManager;
    }

    /**
     * Returns the content encryption algorithm manager.
     */
    public function getContentEncryptionAlgorithmManager(): AlgorithmManager
    {
        return $this->contentEncryptionAlgorithmManager;
    }

    /**
     * Returns the compression method manager.
     */
    public function getCompressionMethodManager(): CompressionMethodManager
    {
        return $this->compressionMethodManager;
    }

    /**
     * This method will try to decrypt the given JWE and recipient using a JWK.
     *
     * @param JWE $jwe       A JWE object to decrypt
     * @param JWK $jwk       The key used to decrypt the input
     * @param int $recipient The recipient used to decrypt the token
     */
    public function decryptUsingKey(JWE &$jwe, JWK $jwk, int $recipient, ?JWK $senderKey = null): bool
    {
        $jwkset = new JWKSet([$jwk]);

        return $this->decryptUsingKeySet($jwe, $jwkset, $recipient, $senderKey);
    }

    /**
     * This method will try to decrypt the given JWE and recipient using a JWKSet.
     *
     * @param JWE    $jwe       A JWE object to decrypt
     * @param JWKSet $jwkset    The key set used to decrypt the input
     * @param JWK    $jwk       The key used to decrypt the token in case of success
     * @param int    $recipient The recipient used to decrypt the token in case of success
     */
    public function decryptUsingKeySet(
        JWE &$jwe,
        JWKSet $jwkset,
        int $recipient,
        JWK &$jwk = null,
        ?JWK $senderKey = null
    ): bool {
        if ($jwkset->count() === 0) {
            throw new InvalidArgumentException('No key in the key set.');
        }
        if ($jwe->getPayload() !== null) {
            return true;
        }
        if ($jwe->countRecipients() === 0) {
            throw new InvalidArgumentException('The JWE does not contain any recipient.');
        }

        $plaintext = $this->decryptRecipientKey($jwe, $jwkset, $recipient, $jwk, $senderKey);
        if ($plaintext !== null) {
            $jwe = $jwe->withPayload($plaintext);

            return true;
        }

        return false;
    }

    private function decryptRecipientKey(
        JWE $jwe,
        JWKSet $jwkset,
        int $i,
        JWK &$successJwk = null,
        ?JWK $senderKey = null
    ): ?string {
        $recipient = $jwe->getRecipient($i);
        $completeHeader = array_merge(
            $jwe->getSharedProtectedHeader(),
            $jwe->getSharedHeader(),
            $recipient->getHeader()
        );
        $this->checkCompleteHeader($completeHeader);

        $key_encryption_algorithm = $this->getKeyEncryptionAlgorithm($completeHeader);
        $content_encryption_algorithm = $this->getContentEncryptionAlgorithm($completeHeader);

        $this->checkIvSize($jwe->getIV(), $content_encryption_algorithm->getIVSize());

        foreach ($jwkset as $recipientKey) {
            try {
                KeyChecker::checkKeyUsage($recipientKey, 'decryption');
                if ($key_encryption_algorithm->name() !== 'dir') {
                    KeyChecker::checkKeyAlgorithm($recipientKey, $key_encryption_algorithm->name());
                } else {
                    KeyChecker::checkKeyAlgorithm($recipientKey, $content_encryption_algorithm->name());
                }
                $cek = $this->decryptCEK(
                    $key_encryption_algorithm,
                    $content_encryption_algorithm,
                    $recipientKey,
                    $senderKey,
                    $recipient,
                    $completeHeader
                );
                $this->checkCekSize($cek, $key_encryption_algorithm, $content_encryption_algorithm);
                $payload = $this->decryptPayload($jwe, $cek, $content_encryption_algorithm, $completeHeader);
                $successJwk = $recipientKey;

                return $payload;
            } catch (Throwable) {
                //We do nothing, we continue with other keys
                continue;
            }
        }

        return null;
    }

    private function checkCekSize(
        string $cek,
        KeyEncryptionAlgorithm $keyEncryptionAlgorithm,
        ContentEncryptionAlgorithm $algorithm
    ): void {
        if ($keyEncryptionAlgorithm instanceof DirectEncryption || $keyEncryptionAlgorithm instanceof KeyAgreement) {
            return;
        }
        if (mb_strlen($cek, '8bit') * 8 !== $algorithm->getCEKSize()) {
            throw new InvalidArgumentException('Invalid CEK size');
        }
    }

    private function checkIvSize(?string $iv, int $requiredIvSize): void
    {
        if ($iv === null && $requiredIvSize !== 0) {
            throw new InvalidArgumentException('Invalid IV size');
        }
        if (is_string($iv) && mb_strlen($iv, '8bit') !== $requiredIvSize / 8) {
            throw new InvalidArgumentException('Invalid IV size');
        }
    }

    private function decryptCEK(
        Algorithm $key_encryption_algorithm,
        ContentEncryptionAlgorithm $content_encryption_algorithm,
        JWK $recipientKey,
        ?JWK $senderKey,
        Recipient $recipient,
        array $completeHeader
    ): string {
        if ($key_encryption_algorithm instanceof DirectEncryption) {
            return $key_encryption_algorithm->getCEK($recipientKey);
        }
        if ($key_encryption_algorithm instanceof KeyAgreement) {
            return $key_encryption_algorithm->getAgreementKey(
                $content_encryption_algorithm->getCEKSize(),
                $content_encryption_algorithm->name(),
                $recipientKey,
                $senderKey,
                $completeHeader
            );
        }
        if ($key_encryption_algorithm instanceof KeyAgreementWithKeyWrapping) {
            return $key_encryption_algorithm->unwrapAgreementKey(
                $recipientKey,
                $senderKey,
                $recipient->getEncryptedKey() ?? '',
                $content_encryption_algorithm->getCEKSize(),
                $completeHeader
            );
        }
        if ($key_encryption_algorithm instanceof KeyEncryption) {
            return $key_encryption_algorithm->decryptKey(
                $recipientKey,
                $recipient->getEncryptedKey() ?? '',
                $completeHeader
            );
        }
        if ($key_encryption_algorithm instanceof KeyWrapping) {
            return $key_encryption_algorithm->unwrapKey(
                $recipientKey,
                $recipient->getEncryptedKey() ?? '',
                $completeHeader
            );
        }

        throw new InvalidArgumentException('Unsupported CEK generation');
    }

    private function decryptPayload(
        JWE $jwe,
        string $cek,
        ContentEncryptionAlgorithm $content_encryption_algorithm,
        array $completeHeader
    ): string {
        $payload = $content_encryption_algorithm->decryptContent(
            $jwe->getCiphertext() ?? '',
            $cek,
            $jwe->getIV() ?? '',
            $jwe->getAAD(),
            $jwe->getEncodedSharedProtectedHeader(),
            $jwe->getTag() ?? ''
        );

        return $this->decompressIfNeeded($payload, $completeHeader);
    }

    private function decompressIfNeeded(string $payload, array $completeHeaders): string
    {
        if (array_key_exists('zip', $completeHeaders)) {
            $compression_method = $this->compressionMethodManager->get($completeHeaders['zip']);
            $payload = $compression_method->uncompress($payload);
        }

        return $payload;
    }

    private function checkCompleteHeader(array $completeHeaders): void
    {
        foreach (['enc', 'alg'] as $key) {
            if (! isset($completeHeaders[$key])) {
                throw new InvalidArgumentException(sprintf("Parameter '%s' is missing.", $key));
            }
        }
    }

    private function getKeyEncryptionAlgorithm(array $completeHeaders): KeyEncryptionAlgorithm
    {
        $key_encryption_algorithm = $this->keyEncryptionAlgorithmManager->get($completeHeaders['alg']);
        if (! $key_encryption_algorithm instanceof KeyEncryptionAlgorithm) {
            throw new InvalidArgumentException(sprintf(
                'The key encryption algorithm "%s" is not supported or does not implement KeyEncryptionAlgorithm interface.',
                $completeHeaders['alg']
            ));
        }

        return $key_encryption_algorithm;
    }

    private function getContentEncryptionAlgorithm(array $completeHeader): ContentEncryptionAlgorithm
    {
        $content_encryption_algorithm = $this->contentEncryptionAlgorithmManager->get($completeHeader['enc']);
        if (! $content_encryption_algorithm instanceof ContentEncryptionAlgorithm) {
            throw new InvalidArgumentException(sprintf(
                'The key encryption algorithm "%s" is not supported or does not implement the ContentEncryption interface.',
                $completeHeader['enc']
            ));
        }

        return $content_encryption_algorithm;
    }
}