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<?php

namespace Aws\Crypto;

use GuzzleHttp\Psr7;

use GuzzleHttp\Psr7\AppendStream;

use GuzzleHttp\Psr7\Stream;

trait EncryptionTrait

{

    private static $allowedOptions = [

        'Cipher' => true,

        'KeySize' => true,

        'Aad' => true,

    ];

    /**

     * Dependency to generate a CipherMethod from a set of inputs for loading

     * in to an AesEncryptingStream.

     *

     * @param string $cipherName Name of the cipher to generate for encrypting.

     * @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 and populates encryption metadata into the

     * supplied envelope.

     *

     * @param Stream $plaintext Plain-text data to be encrypted using the

     *                          materials, algorithm, and data provided.

     * @param array $cipherOptions Options for use in determining the cipher to

     *                             be used for encrypting data.

     * @param MaterialsProvider $provider A provider to supply and encrypt

     *                                    materials used in encryption.

     * @param MetadataEnvelope $envelope A storage envelope for encryption

     *                                   metadata to be added to.

     *

     * @return AesStreamInterface

     *

     * @throws \InvalidArgumentException Thrown when a value in $cipherOptions

     *                                   is not valid.

     *

     * @internal

     */

    public function encrypt(

        Stream $plaintext,

        array $cipherOptions,

        MaterialsProvider $provider,

        MetadataEnvelope $envelope

    ) {

        $materialsDescription = $provider->getMaterialsDescription();

        $cipherOptions = array_intersect_key(

            $cipherOptions,

            self::$allowedOptions

        );

        if (empty($cipherOptions['Cipher'])) {

            throw new \InvalidArgumentException('An encryption cipher must be'

                . ' specified in the "cipher_options".');

        }

        if (!self::isSupportedCipher($cipherOptions['Cipher'])) {

            throw new \InvalidArgumentException('The cipher requested is not'

                . ' supported by the SDK.');

        }

        if (empty($cipherOptions['KeySize'])) {

            $cipherOptions['KeySize'] = 256;

        }

        if (!is_int($cipherOptions['KeySize'])) {

            throw new \InvalidArgumentException('The cipher "KeySize" must be'

                . ' an integer.');

        }

        if (!MaterialsProvider::isSupportedKeySize(

            $cipherOptions['KeySize']

        )) {

            throw new \InvalidArgumentException('The cipher "KeySize" requested'

                . ' is not supported by AES (128, 192, or 256).');

        }

        $cipherOptions['Iv'] = $provider->generateIv(

            $this->getCipherOpenSslName(

                $cipherOptions['Cipher'],

                $cipherOptions['KeySize']

            )

        );

        $cek = $provider->generateCek($cipherOptions['KeySize']);

        list($encryptingStream, $aesName) = $this->getEncryptingStream(

            $plaintext,

            $cek,

            $cipherOptions

        );

        // Populate envelope data

        $envelope[MetadataEnvelope::CONTENT_KEY_V2_HEADER] =

            $provider->encryptCek(

                $cek,

                $materialsDescription

            );

        unset($cek);

        $envelope[MetadataEnvelope::IV_HEADER] =

            base64_encode($cipherOptions['Iv']);

        $envelope[MetadataEnvelope::KEY_WRAP_ALGORITHM_HEADER] =

            $provider->getWrapAlgorithmName();

        $envelope[MetadataEnvelope::CONTENT_CRYPTO_SCHEME_HEADER] = $aesName;

        $envelope[MetadataEnvelope::UNENCRYPTED_CONTENT_LENGTH_HEADER] =

            strlen($plaintext);

        $envelope[MetadataEnvelope::MATERIALS_DESCRIPTION_HEADER] =

            json_encode($materialsDescription);

        if (!empty($cipherOptions['Tag'])) {

            $envelope[MetadataEnvelope::CRYPTO_TAG_LENGTH_HEADER] =

                strlen($cipherOptions['Tag']) * 8;

        }

        return $encryptingStream;

    }

    /**

     * Generates a stream that wraps the plaintext with the proper cipher and

     * uses the content encryption key (CEK) to encrypt the data when read.

     *

     * @param Stream $plaintext 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, string]

     *

     * @internal

     */

    protected function getEncryptingStream(

        Stream $plaintext,

        $cek,

        &$cipherOptions

    ) {

        switch ($cipherOptions['Cipher']) {

            case 'gcm':

                $cipherOptions['TagLength'] = 16;

                $cipherTextStream = new AesGcmEncryptingStream(

                    $plaintext,

                    $cek,

                    $cipherOptions['Iv'],

                    $cipherOptions['Aad'] = isset($cipherOptions['Aad'])

                        ? $cipherOptions['Aad']

                        : '',

                    $cipherOptions['TagLength'],

                    $cipherOptions['KeySize']

                );

                if (!empty($cipherOptions['Aad'])) {

                    trigger_error("'Aad' has been supplied for content encryption"

                        . " with " . $cipherTextStream->getAesName() . ". The"

                        . " PHP SDK encryption client can decrypt an object"

                        . " encrypted in this way, but other AWS SDKs may not be"

                        . " able to.", E_USER_WARNING);

                }

                $appendStream = new AppendStream([

                    $cipherTextStream->createStream()

                ]);

                $cipherOptions['Tag'] = $cipherTextStream->getTag();

                $appendStream->addStream(Psr7\Utils::streamFor($cipherOptions['Tag']));

                return [$appendStream, $cipherTextStream->getAesName()];

            default:

                $cipherMethod = $this->buildCipherMethod(

                    $cipherOptions['Cipher'],

                    $cipherOptions['Iv'],

                    $cipherOptions['KeySize']

                );

                $cipherTextStream = new AesEncryptingStream(

                    $plaintext,

                    $cek,

                    $cipherMethod

                );

                return [$cipherTextStream, $cipherTextStream->getAesName()];

        }

    }

}