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<?php
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namespace Aws\Crypto;
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use GuzzleHttp\Psr7\StreamDecoratorTrait;
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use \LogicException;
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use Psr\Http\Message\StreamInterface;
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use Aws\Crypto\Cipher\CipherMethod;
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/**
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 * @internal Represents a stream of data to be decrypted with passed cipher.
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 */
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class AesDecryptingStream implements AesStreamInterface
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{
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    const BLOCK_SIZE = 16; // 128 bits
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    use StreamDecoratorTrait;
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    /**
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     * @var string
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     */
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    private $buffer = '';
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    /**
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     * @var CipherMethod
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     */
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    private $cipherMethod;
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    /**
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     * @var string
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     */
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    private $key;
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    /**
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     * @var StreamInterface
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     */
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    private $stream;
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    /**
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     * @param StreamInterface $cipherText
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     * @param string $key
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     * @param CipherMethod $cipherMethod
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     */
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    public function __construct(
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        StreamInterface $cipherText,
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        $key,
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        CipherMethod $cipherMethod
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    ) {
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        $this->stream = $cipherText;
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        $this->key = $key;
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        $this->cipherMethod = clone $cipherMethod;
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    }
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    public function getOpenSslName()
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    {
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        return $this->cipherMethod->getOpenSslName();
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    }
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    public function getAesName()
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    {
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        return $this->cipherMethod->getAesName();
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    }
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    public function getCurrentIv()
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    {
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        return $this->cipherMethod->getCurrentIv();
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    }
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    public function getSize()
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    {
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        $plainTextSize = $this->stream->getSize();
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        if ($this->cipherMethod->requiresPadding()) {
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            // PKCS7 padding requires that between 1 and self::BLOCK_SIZE be
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            // added to the plaintext to make it an even number of blocks. The
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            // plaintext is between strlen($cipherText) - self::BLOCK_SIZE and
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            // strlen($cipherText) - 1
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            return null;
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        }
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        return $plainTextSize;
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    }
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    public function isWritable()
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    {
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        return false;
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    }
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    public function read($length)
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    {
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        if ($length > strlen($this->buffer)) {
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            $this->buffer .= $this->decryptBlock(
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                (int) (
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                        self::BLOCK_SIZE * ceil(($length - strlen($this->buffer)) / self::BLOCK_SIZE)
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                )
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            );
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        }
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        $data = substr($this->buffer, 0, $length);
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        $this->buffer = substr($this->buffer, $length);
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        return $data ? $data : '';
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    }
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    public function seek($offset, $whence = SEEK_SET)
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    {
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        if ($offset === 0 && $whence === SEEK_SET) {
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            $this->buffer = '';
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            $this->cipherMethod->seek(0, SEEK_SET);
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            $this->stream->seek(0, SEEK_SET);
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        } else {
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            throw new LogicException('AES encryption streams only support being'
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                . ' rewound, not arbitrary seeking.');
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        }
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    }
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    private function decryptBlock($length)
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    {
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        if ($this->stream->eof()) {
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            return '';
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        }
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        $cipherText = '';
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        do {
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            $cipherText .= $this->stream->read((int) ($length - strlen($cipherText)));
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        } while (strlen($cipherText) < $length && !$this->stream->eof());
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        $options = OPENSSL_RAW_DATA;
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        if (!$this->stream->eof()
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            && $this->stream->getSize() !== $this->stream->tell()
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        ) {
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            $options |= OPENSSL_ZERO_PADDING;
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        }
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        $plaintext = openssl_decrypt(
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            $cipherText,
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            $this->cipherMethod->getOpenSslName(),
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            $this->key,
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            $options,
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            $this->cipherMethod->getCurrentIv()
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        );
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        $this->cipherMethod->update($cipherText);
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        return $plaintext;
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    }
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}