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<?php
namespace Aws\Crypto;
use Aws\Exception\CryptoException;
use GuzzleHttp\Psr7;
use GuzzleHttp\Psr7\LimitStream;
use Psr\Http\Message\StreamInterface;
trait DecryptionTraitV2
{
/**
* Dependency to reverse lookup the openssl_* cipher name from the AESName
* in the MetadataEnvelope.
*
* @param $aesName
*
* @return string
*
* @internal
*/
abstract protected function getCipherFromAesName($aesName);
/**
* Dependency to generate a CipherMethod from a set of inputs for loading
* in to an AesDecryptingStream.
*
* @param string $cipherName Name of the cipher to generate for decrypting.
* @param string $iv Base Initialization Vector for the cipher.
* @param int $keySize Size of the encryption key, in bits, that will be
* used.
*
* @return Cipher\CipherMethod
*
* @internal
*/
abstract protected function buildCipherMethod($cipherName, $iv, $keySize);
/**
* Builds an AesStreamInterface using cipher options loaded from the
* MetadataEnvelope and MaterialsProvider. Can decrypt data from both the
* legacy and V2 encryption client workflows.
*
* @param string $cipherText Plain-text data to be encrypted using the
* materials, algorithm, and data provided.
* @param MaterialsProviderInterfaceV2 $provider A provider to supply and encrypt
* materials used in encryption.
* @param MetadataEnvelope $envelope A storage envelope for encryption
* metadata to be read from.
* @param array $options Options used for decryption.
*
* @return AesStreamInterface
*
* @throws \InvalidArgumentException Thrown when a value in $cipherOptions
* is not valid.
*
* @internal
*/
public function decrypt(
$cipherText,
MaterialsProviderInterfaceV2 $provider,
MetadataEnvelope $envelope,
array $options = []
) {
$options['@CipherOptions'] = !empty($options['@CipherOptions'])
? $options['@CipherOptions']
: [];
$options['@CipherOptions']['Iv'] = base64_decode(
$envelope[MetadataEnvelope::IV_HEADER]
);
$options['@CipherOptions']['TagLength'] =
$envelope[MetadataEnvelope::CRYPTO_TAG_LENGTH_HEADER] / 8;
$cek = $provider->decryptCek(
base64_decode(
$envelope[MetadataEnvelope::CONTENT_KEY_V2_HEADER]
),
json_decode(
$envelope[MetadataEnvelope::MATERIALS_DESCRIPTION_HEADER],
true
),
$options
);
$options['@CipherOptions']['KeySize'] = strlen($cek) * 8;
$options['@CipherOptions']['Cipher'] = $this->getCipherFromAesName(
$envelope[MetadataEnvelope::CONTENT_CRYPTO_SCHEME_HEADER]
);
$this->validateOptionsAndEnvelope($options, $envelope);
$decryptionStream = $this->getDecryptingStream(
$cipherText,
$cek,
$options['@CipherOptions']
);
unset($cek);
return $decryptionStream;
}
private function getTagFromCiphertextStream(
StreamInterface $cipherText,
$tagLength
) {
$cipherTextSize = $cipherText->getSize();
if ($cipherTextSize == null || $cipherTextSize <= 0) {
throw new \RuntimeException('Cannot decrypt a stream of unknown'
. ' size.');
}
return (string) new LimitStream(
$cipherText,
$tagLength,
$cipherTextSize - $tagLength
);
}
private function getStrippedCiphertextStream(
StreamInterface $cipherText,
$tagLength
) {
$cipherTextSize = $cipherText->getSize();
if ($cipherTextSize == null || $cipherTextSize <= 0) {
throw new \RuntimeException('Cannot decrypt a stream of unknown'
. ' size.');
}
return new LimitStream(
$cipherText,
$cipherTextSize - $tagLength,
0
);
}
private function validateOptionsAndEnvelope($options, $envelope)
{
$allowedCiphers = AbstractCryptoClientV2::$supportedCiphers;
$allowedKeywraps = AbstractCryptoClientV2::$supportedKeyWraps;
if ($options['@SecurityProfile'] == 'V2_AND_LEGACY') {
$allowedCiphers = array_unique(array_merge(
$allowedCiphers,
AbstractCryptoClient::$supportedCiphers
));
$allowedKeywraps = array_unique(array_merge(
$allowedKeywraps,
AbstractCryptoClient::$supportedKeyWraps
));
}
$v1SchemaException = new CryptoException("The requested object is encrypted"
. " with V1 encryption schemas that have been disabled by"
. " client configuration @SecurityProfile=V2. Retry with"
. " V2_AND_LEGACY enabled or reencrypt the object.");
if (!in_array($options['@CipherOptions']['Cipher'], $allowedCiphers)) {
if (in_array($options['@CipherOptions']['Cipher'], AbstractCryptoClient::$supportedCiphers)) {
throw $v1SchemaException;
}
throw new CryptoException("The requested object is encrypted with"
. " the cipher '{$options['@CipherOptions']['Cipher']}', which is not"
. " supported for decryption with the selected security profile."
. " This profile allows decryption with: "
. implode(", ", $allowedCiphers));
}
if (!in_array(
$envelope[MetadataEnvelope::KEY_WRAP_ALGORITHM_HEADER],
$allowedKeywraps
)) {
if (in_array(
$envelope[MetadataEnvelope::KEY_WRAP_ALGORITHM_HEADER],
AbstractCryptoClient::$supportedKeyWraps)
) {
throw $v1SchemaException;
}
throw new CryptoException("The requested object is encrypted with"
. " the keywrap schema '{$envelope[MetadataEnvelope::KEY_WRAP_ALGORITHM_HEADER]}',"
. " which is not supported for decryption with the current security"
. " profile.");
}
$matdesc = json_decode(
$envelope[MetadataEnvelope::MATERIALS_DESCRIPTION_HEADER],
true
);
if (isset($matdesc['aws:x-amz-cek-alg'])
&& $envelope[MetadataEnvelope::CONTENT_CRYPTO_SCHEME_HEADER] !==
$matdesc['aws:x-amz-cek-alg']
) {
throw new CryptoException("There is a mismatch in specified content"
. " encryption algrithm between the materials description value"
. " and the metadata envelope value: {$matdesc['aws:x-amz-cek-alg']}"
. " vs. {$envelope[MetadataEnvelope::CONTENT_CRYPTO_SCHEME_HEADER]}.");
}
}
/**
* Generates a stream that wraps the cipher text with the proper cipher and
* uses the content encryption key (CEK) to decrypt the data when read.
*
* @param string $cipherText Plain-text data to be encrypted using the
* materials, algorithm, and data provided.
* @param string $cek A content encryption key for use by the stream for
* encrypting the plaintext data.
* @param array $cipherOptions Options for use in determining the cipher to
* be used for encrypting data.
*
* @return AesStreamInterface
*
* @internal
*/
protected function getDecryptingStream(
$cipherText,
$cek,
$cipherOptions
) {
$cipherTextStream = Psr7\Utils::streamFor($cipherText);
switch ($cipherOptions['Cipher']) {
case 'gcm':
$cipherOptions['Tag'] = $this->getTagFromCiphertextStream(
$cipherTextStream,
$cipherOptions['TagLength']
);
return new AesGcmDecryptingStream(
$this->getStrippedCiphertextStream(
$cipherTextStream,
$cipherOptions['TagLength']
),
$cek,
$cipherOptions['Iv'],
$cipherOptions['Tag'],
$cipherOptions['Aad'] = isset($cipherOptions['Aad'])
? $cipherOptions['Aad']
: '',
$cipherOptions['TagLength'] ?: null,
$cipherOptions['KeySize']
);
default:
$cipherMethod = $this->buildCipherMethod(
$cipherOptions['Cipher'],
$cipherOptions['Iv'],
$cipherOptions['KeySize']
);
return new AesDecryptingStream(
$cipherTextStream,
$cek,
$cipherMethod
);
}
}
}
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