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<?php
namespace Aws\Crypto;
use GuzzleHttp\Psr7;
use GuzzleHttp\Psr7\LimitStream;
use Psr\Http\Message\StreamInterface;
trait DecryptionTrait
{
/**
* 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 MaterialsProviderInterface $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 $cipherOptions Additional verification options.
*
* @return AesStreamInterface
*
* @throws \InvalidArgumentException Thrown when a value in $cipherOptions
* is not valid.
*
* @internal
*/
public function decrypt(
$cipherText,
MaterialsProviderInterface $provider,
MetadataEnvelope $envelope,
array $cipherOptions = []
) {
$cipherOptions['Iv'] = base64_decode(
$envelope[MetadataEnvelope::IV_HEADER]
);
$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
)
);
$cipherOptions['KeySize'] = strlen($cek) * 8;
$cipherOptions['Cipher'] = $this->getCipherFromAesName(
$envelope[MetadataEnvelope::CONTENT_CRYPTO_SCHEME_HEADER]
);
$decryptionStream = $this->getDecryptingStream(
$cipherText,
$cek,
$cipherOptions
);
unset($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
);
}
/**
* 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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