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<?php
namespace Firebase\JWT;
use DomainException;
use InvalidArgumentException;
use UnexpectedValueException;
/**
* JSON Web Key implementation, based on this spec:
* https://tools.ietf.org/html/draft-ietf-jose-json-web-key-41
*
* PHP version 5
*
* @category Authentication
* @package Authentication_JWT
* @author Bui Sy Nguyen <nguyenbs@gmail.com>
* @license http://opensource.org/licenses/BSD-3-Clause 3-clause BSD
* @link https://github.com/firebase/php-jwt
*/
class JWK
{
/**
* Parse a set of JWK keys
*
* @param array<mixed> $jwks The JSON Web Key Set as an associative array
*
* @return array<string, Key> An associative array of key IDs (kid) to Key objects
*
* @throws InvalidArgumentException Provided JWK Set is empty
* @throws UnexpectedValueException Provided JWK Set was invalid
* @throws DomainException OpenSSL failure
*
* @uses parseKey
*/
public static function parseKeySet(array $jwks): array
{
$keys = [];
if (!isset($jwks['keys'])) {
throw new UnexpectedValueException('"keys" member must exist in the JWK Set');
}
if (empty($jwks['keys'])) {
throw new InvalidArgumentException('JWK Set did not contain any keys');
}
foreach ($jwks['keys'] as $k => $v) {
$kid = isset($v['kid']) ? $v['kid'] : $k;
if ($key = self::parseKey($v)) {
$keys[(string) $kid] = $key;
}
}
if (0 === \count($keys)) {
throw new UnexpectedValueException('No supported algorithms found in JWK Set');
}
return $keys;
}
/**
* Parse a JWK key
*
* @param array<mixed> $jwk An individual JWK
*
* @return Key The key object for the JWK
*
* @throws InvalidArgumentException Provided JWK is empty
* @throws UnexpectedValueException Provided JWK was invalid
* @throws DomainException OpenSSL failure
*
* @uses createPemFromModulusAndExponent
*/
public static function parseKey(array $jwk): ?Key
{
if (empty($jwk)) {
throw new InvalidArgumentException('JWK must not be empty');
}
if (!isset($jwk['kty'])) {
throw new UnexpectedValueException('JWK must contain a "kty" parameter');
}
if (!isset($jwk['alg'])) {
// The "alg" parameter is optional in a KTY, but is required for parsing in
// this library. Add it manually to your JWK array if it doesn't already exist.
// @see https://datatracker.ietf.org/doc/html/rfc7517#section-4.4
throw new UnexpectedValueException('JWK must contain an "alg" parameter');
}
switch ($jwk['kty']) {
case 'RSA':
if (!empty($jwk['d'])) {
throw new UnexpectedValueException('RSA private keys are not supported');
}
if (!isset($jwk['n']) || !isset($jwk['e'])) {
throw new UnexpectedValueException('RSA keys must contain values for both "n" and "e"');
}
$pem = self::createPemFromModulusAndExponent($jwk['n'], $jwk['e']);
$publicKey = \openssl_pkey_get_public($pem);
if (false === $publicKey) {
throw new DomainException(
'OpenSSL error: ' . \openssl_error_string()
);
}
return new Key($publicKey, $jwk['alg']);
default:
// Currently only RSA is supported
break;
}
return null;
}
/**
* Create a public key represented in PEM format from RSA modulus and exponent information
*
* @param string $n The RSA modulus encoded in Base64
* @param string $e The RSA exponent encoded in Base64
*
* @return string The RSA public key represented in PEM format
*
* @uses encodeLength
*/
private static function createPemFromModulusAndExponent(
string $n,
string $e
): string {
$mod = JWT::urlsafeB64Decode($n);
$exp = JWT::urlsafeB64Decode($e);
$modulus = \pack('Ca*a*', 2, self::encodeLength(\strlen($mod)), $mod);
$publicExponent = \pack('Ca*a*', 2, self::encodeLength(\strlen($exp)), $exp);
$rsaPublicKey = \pack(
'Ca*a*a*',
48,
self::encodeLength(\strlen($modulus) + \strlen($publicExponent)),
$modulus,
$publicExponent
);
// sequence(oid(1.2.840.113549.1.1.1), null)) = rsaEncryption.
$rsaOID = \pack('H*', '300d06092a864886f70d0101010500'); // hex version of MA0GCSqGSIb3DQEBAQUA
$rsaPublicKey = \chr(0) . $rsaPublicKey;
$rsaPublicKey = \chr(3) . self::encodeLength(\strlen($rsaPublicKey)) . $rsaPublicKey;
$rsaPublicKey = \pack(
'Ca*a*',
48,
self::encodeLength(\strlen($rsaOID . $rsaPublicKey)),
$rsaOID . $rsaPublicKey
);
$rsaPublicKey = "-----BEGIN PUBLIC KEY-----\r\n" .
\chunk_split(\base64_encode($rsaPublicKey), 64) .
'-----END PUBLIC KEY-----';
return $rsaPublicKey;
}
/**
* DER-encode the length
*
* DER supports lengths up to (2**8)**127, however, we'll only support lengths up to (2**8)**4. See
* {@link http://itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf#p=13 X.690 paragraph 8.1.3} for more information.
*
* @param int $length
* @return string
*/
private static function encodeLength(int $length): string
{
if ($length <= 0x7F) {
return \chr($length);
}
$temp = \ltrim(\pack('N', $length), \chr(0));
return \pack('Ca*', 0x80 | \strlen($temp), $temp);
}
}
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