424 lines
15 KiB
PHP
424 lines
15 KiB
PHP
<?php
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declare(strict_types=1);
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/*
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* This file is part of the WebPush library.
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*
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* (c) Louis Lagrange <lagrange.louis@gmail.com>
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*/
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namespace Minishlink\WebPush;
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use Base64Url\Base64Url;
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use Brick\Math\BigInteger;
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use Jose\Component\Core\JWK;
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use Jose\Component\Core\Util\Ecc\NistCurve;
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use Jose\Component\Core\Util\Ecc\PrivateKey;
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use Jose\Component\Core\Util\ECKey;
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class Encryption
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{
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public const MAX_PAYLOAD_LENGTH = 4078;
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public const MAX_COMPATIBILITY_PAYLOAD_LENGTH = 3052;
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/**
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* @param string $payload
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* @param int $maxLengthToPad
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* @param string $contentEncoding
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* @return string padded payload (plaintext)
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* @throws \ErrorException
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*/
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public static function padPayload(string $payload, int $maxLengthToPad, string $contentEncoding): string
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{
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$payloadLen = Utils::safeStrlen($payload);
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$padLen = $maxLengthToPad ? $maxLengthToPad - $payloadLen : 0;
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if ($contentEncoding === "aesgcm") {
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return pack('n*', $padLen).str_pad($payload, $padLen + $payloadLen, chr(0), STR_PAD_LEFT);
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} elseif ($contentEncoding === "aes128gcm") {
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return str_pad($payload.chr(2), $padLen + $payloadLen, chr(0), STR_PAD_RIGHT);
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} else {
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throw new \ErrorException("This content encoding is not supported");
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}
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}
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/**
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* @param string $payload With padding
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* @param string $userPublicKey Base 64 encoded (MIME or URL-safe)
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* @param string $userAuthToken Base 64 encoded (MIME or URL-safe)
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* @param string $contentEncoding
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* @return array
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*
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* @throws \ErrorException
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*/
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public static function encrypt(string $payload, string $userPublicKey, string $userAuthToken, string $contentEncoding): array
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{
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return self::deterministicEncrypt(
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$payload,
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$userPublicKey,
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$userAuthToken,
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$contentEncoding,
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self::createLocalKeyObject(),
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random_bytes(16)
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);
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}
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/**
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* @param string $payload
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* @param string $userPublicKey
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* @param string $userAuthToken
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* @param string $contentEncoding
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* @param array $localKeyObject
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* @param string $salt
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* @return array
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*
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* @throws \ErrorException
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*/
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public static function deterministicEncrypt(string $payload, string $userPublicKey, string $userAuthToken, string $contentEncoding, array $localKeyObject, string $salt): array
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{
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$userPublicKey = Base64Url::decode($userPublicKey);
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$userAuthToken = Base64Url::decode($userAuthToken);
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// get local key pair
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if (count($localKeyObject) === 1) {
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/** @var JWK $localJwk */
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$localJwk = current($localKeyObject);
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$localPublicKey = hex2bin(Utils::serializePublicKeyFromJWK($localJwk));
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} else {
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/** @var PrivateKey $localPrivateKeyObject */
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list($localPublicKeyObject, $localPrivateKeyObject) = $localKeyObject;
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$localPublicKey = hex2bin(Utils::serializePublicKey($localPublicKeyObject));
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$localJwk = new JWK([
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'kty' => 'EC',
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'crv' => 'P-256',
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'd' => Base64Url::encode($localPrivateKeyObject->getSecret()->toBytes(false)),
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'x' => Base64Url::encode($localPublicKeyObject[0]),
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'y' => Base64Url::encode($localPublicKeyObject[1]),
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]);
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}
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if (!$localPublicKey) {
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throw new \ErrorException('Failed to convert local public key from hexadecimal to binary');
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}
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// get user public key object
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[$userPublicKeyObjectX, $userPublicKeyObjectY] = Utils::unserializePublicKey($userPublicKey);
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$userJwk = new JWK([
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'kty' => 'EC',
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'crv' => 'P-256',
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'x' => Base64Url::encode($userPublicKeyObjectX),
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'y' => Base64Url::encode($userPublicKeyObjectY),
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]);
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// get shared secret from user public key and local private key
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$sharedSecret = self::calculateAgreementKey($localJwk, $userJwk);
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$sharedSecret = str_pad($sharedSecret, 32, chr(0), STR_PAD_LEFT);
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if (!$sharedSecret) {
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throw new \ErrorException('Failed to convert shared secret from hexadecimal to binary');
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}
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// section 4.3
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$ikm = self::getIKM($userAuthToken, $userPublicKey, $localPublicKey, $sharedSecret, $contentEncoding);
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// section 4.2
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$context = self::createContext($userPublicKey, $localPublicKey, $contentEncoding);
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// derive the Content Encryption Key
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$contentEncryptionKeyInfo = self::createInfo($contentEncoding, $context, $contentEncoding);
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$contentEncryptionKey = self::hkdf($salt, $ikm, $contentEncryptionKeyInfo, 16);
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// section 3.3, derive the nonce
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$nonceInfo = self::createInfo('nonce', $context, $contentEncoding);
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$nonce = self::hkdf($salt, $ikm, $nonceInfo, 12);
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// encrypt
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// "The additional data passed to each invocation of AEAD_AES_128_GCM is a zero-length octet sequence."
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$tag = '';
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$encryptedText = openssl_encrypt($payload, 'aes-128-gcm', $contentEncryptionKey, OPENSSL_RAW_DATA, $nonce, $tag);
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// return values in url safe base64
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return [
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'localPublicKey' => $localPublicKey,
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'salt' => $salt,
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'cipherText' => $encryptedText.$tag,
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];
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}
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public static function getContentCodingHeader(string $salt, string $localPublicKey, string $contentEncoding): string
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{
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if ($contentEncoding === "aes128gcm") {
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return $salt
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.pack('N*', 4096)
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.pack('C*', Utils::safeStrlen($localPublicKey))
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.$localPublicKey;
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}
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return "";
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}
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/**
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* HMAC-based Extract-and-Expand Key Derivation Function (HKDF).
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*
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* This is used to derive a secure encryption key from a mostly-secure shared
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* secret.
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*
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* This is a partial implementation of HKDF tailored to our specific purposes.
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* In particular, for us the value of N will always be 1, and thus T always
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* equals HMAC-Hash(PRK, info | 0x01).
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*
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* See {@link https://www.rfc-editor.org/rfc/rfc5869.txt}
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* From {@link https://github.com/GoogleChrome/push-encryption-node/blob/master/src/encrypt.js}
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*
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* @param string $salt A non-secret random value
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* @param string $ikm Input keying material
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* @param string $info Application-specific context
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* @param int $length The length (in bytes) of the required output key
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*
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* @return string
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*/
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private static function hkdf(string $salt, string $ikm, string $info, int $length): string
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{
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// extract
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$prk = hash_hmac('sha256', $ikm, $salt, true);
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// expand
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return mb_substr(hash_hmac('sha256', $info.chr(1), $prk, true), 0, $length, '8bit');
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}
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/**
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* Creates a context for deriving encryption parameters.
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* See section 4.2 of
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* {@link https://tools.ietf.org/html/draft-ietf-httpbis-encryption-encoding-00}
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* From {@link https://github.com/GoogleChrome/push-encryption-node/blob/master/src/encrypt.js}.
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*
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* @param string $clientPublicKey The client's public key
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* @param string $serverPublicKey Our public key
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*
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* @return null|string
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*
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* @throws \ErrorException
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*/
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private static function createContext(string $clientPublicKey, string $serverPublicKey, string $contentEncoding): ?string
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{
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if ($contentEncoding === "aes128gcm") {
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return null;
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}
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if (Utils::safeStrlen($clientPublicKey) !== 65) {
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throw new \ErrorException('Invalid client public key length');
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}
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// This one should never happen, because it's our code that generates the key
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if (Utils::safeStrlen($serverPublicKey) !== 65) {
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throw new \ErrorException('Invalid server public key length');
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}
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$len = chr(0).'A'; // 65 as Uint16BE
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return chr(0).$len.$clientPublicKey.$len.$serverPublicKey;
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}
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/**
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* Returns an info record. See sections 3.2 and 3.3 of
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* {@link https://tools.ietf.org/html/draft-ietf-httpbis-encryption-encoding-00}
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* From {@link https://github.com/GoogleChrome/push-encryption-node/blob/master/src/encrypt.js}.
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*
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* @param string $type The type of the info record
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* @param string|null $context The context for the record
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* @param string $contentEncoding
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* @return string
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*
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* @throws \ErrorException
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*/
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private static function createInfo(string $type, ?string $context, string $contentEncoding): string
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{
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if ($contentEncoding === "aesgcm") {
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if (!$context) {
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throw new \ErrorException('Context must exist');
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}
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if (Utils::safeStrlen($context) !== 135) {
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throw new \ErrorException('Context argument has invalid size');
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}
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return 'Content-Encoding: '.$type.chr(0).'P-256'.$context;
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} elseif ($contentEncoding === "aes128gcm") {
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return 'Content-Encoding: '.$type.chr(0);
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}
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throw new \ErrorException('This content encoding is not supported.');
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}
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/**
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* @return array
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*/
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private static function createLocalKeyObject(): array
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{
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try {
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return self::createLocalKeyObjectUsingOpenSSL();
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} catch (\Exception $e) {
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return self::createLocalKeyObjectUsingPurePhpMethod();
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}
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}
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/**
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* @return array
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*/
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private static function createLocalKeyObjectUsingPurePhpMethod(): array
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{
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$curve = NistCurve::curve256();
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$privateKey = $curve->createPrivateKey();
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$publicKey = $curve->createPublicKey($privateKey);
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if ($publicKey->getPoint()->getX() instanceof BigInteger) {
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return [
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new JWK([
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'kty' => 'EC',
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'crv' => 'P-256',
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'x' => Base64Url::encode(self::addNullPadding($publicKey->getPoint()->getX()->toBytes(false))),
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'y' => Base64Url::encode(self::addNullPadding($publicKey->getPoint()->getY()->toBytes(false))),
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'd' => Base64Url::encode(self::addNullPadding($privateKey->getSecret()->toBytes(false))),
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])
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];
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}
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return [
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new JWK([
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'kty' => 'EC',
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'crv' => 'P-256',
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'x' => Base64Url::encode(self::addNullPadding(hex2bin(gmp_strval($publicKey->getPoint()->getX(), 16)))),
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'y' => Base64Url::encode(self::addNullPadding(hex2bin(gmp_strval($publicKey->getPoint()->getY(), 16)))),
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'd' => Base64Url::encode(self::addNullPadding(hex2bin(gmp_strval($privateKey->getSecret(), 16)))),
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])
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];
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}
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/**
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* @return array
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*/
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private static function createLocalKeyObjectUsingOpenSSL(): array
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{
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$keyResource = openssl_pkey_new([
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'curve_name' => 'prime256v1',
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'private_key_type' => OPENSSL_KEYTYPE_EC,
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]);
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if (!$keyResource) {
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throw new \RuntimeException('Unable to create the key');
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}
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$details = openssl_pkey_get_details($keyResource);
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openssl_pkey_free($keyResource);
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if (!$details) {
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throw new \RuntimeException('Unable to get the key details');
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}
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return [
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new JWK([
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'kty' => 'EC',
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'crv' => 'P-256',
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'x' => Base64Url::encode(self::addNullPadding($details['ec']['x'])),
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'y' => Base64Url::encode(self::addNullPadding($details['ec']['y'])),
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'd' => Base64Url::encode(self::addNullPadding($details['ec']['d'])),
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])
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];
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}
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/**
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* @param string $userAuthToken
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* @param string $userPublicKey
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* @param string $localPublicKey
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* @param string $sharedSecret
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* @param string $contentEncoding
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* @return string
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* @throws \ErrorException
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*/
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private static function getIKM(string $userAuthToken, string $userPublicKey, string $localPublicKey, string $sharedSecret, string $contentEncoding): string
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{
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if (!empty($userAuthToken)) {
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if ($contentEncoding === "aesgcm") {
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$info = 'Content-Encoding: auth'.chr(0);
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} elseif ($contentEncoding === "aes128gcm") {
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$info = "WebPush: info".chr(0).$userPublicKey.$localPublicKey;
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} else {
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throw new \ErrorException("This content encoding is not supported");
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}
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return self::hkdf($userAuthToken, $sharedSecret, $info, 32);
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}
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return $sharedSecret;
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}
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private static function calculateAgreementKey(JWK $private_key, JWK $public_key): string
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{
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if (function_exists('openssl_pkey_derive')) {
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try {
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$publicPem = ECKey::convertPublicKeyToPEM($public_key);
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$privatePem = ECKey::convertPrivateKeyToPEM($private_key);
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$result = openssl_pkey_derive($publicPem, $privatePem, 256); // @phpstan-ignore-line
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if ($result === false) {
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throw new \Exception('Unable to compute the agreement key');
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}
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return $result;
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} catch (\Throwable $throwable) {
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//Does nothing. Will fallback to the pure PHP function
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}
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}
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$curve = NistCurve::curve256();
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try {
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$rec_x = self::convertBase64ToBigInteger($public_key->get('x'));
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$rec_y = self::convertBase64ToBigInteger($public_key->get('y'));
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$sen_d = self::convertBase64ToBigInteger($private_key->get('d'));
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$priv_key = PrivateKey::create($sen_d);
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$pub_key = $curve->getPublicKeyFrom($rec_x, $rec_y);
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return hex2bin(str_pad($curve->mul($pub_key->getPoint(), $priv_key->getSecret())->getX()->toBase(16), 64, '0', STR_PAD_LEFT)); // @phpstan-ignore-line
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} catch (\Throwable $e) {
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$rec_x = self::convertBase64ToGMP($public_key->get('x'));
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$rec_y = self::convertBase64ToGMP($public_key->get('y'));
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$sen_d = self::convertBase64ToGMP($private_key->get('d'));
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$priv_key = PrivateKey::create($sen_d); // @phpstan-ignore-line
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$pub_key = $curve->getPublicKeyFrom($rec_x, $rec_y); // @phpstan-ignore-line
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return hex2bin(gmp_strval($curve->mul($pub_key->getPoint(), $priv_key->getSecret())->getX(), 16)); // @phpstan-ignore-line
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}
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}
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/**
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* @param string $value
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* @return BigInteger
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*/
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private static function convertBase64ToBigInteger(string $value): BigInteger
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{
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$value = unpack('H*', Base64Url::decode($value));
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return BigInteger::fromBase($value[1], 16);
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}
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/**
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* @param string $value
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* @return \GMP
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*/
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private static function convertBase64ToGMP(string $value): \GMP
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{
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$value = unpack('H*', Base64Url::decode($value));
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return gmp_init($value[1], 16);
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}
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private static function addNullPadding(string $data): string
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{
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return str_pad($data, 32, chr(0), STR_PAD_LEFT);
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}
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}
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