SimpleSAML\XMLSecurity\Utils\Security::doDecryptElement()

Complexity

Conditions	18
Paths	98

Size

Total Lines	147
Code Lines	69

Duplication

Lines	0
Ratio	0 %

Importance

Changes	1
Bugs	0	Features	0

<?php
    private static function doDecryptElement(
        DOMElement $encryptedData,
        XMLSecurityKey $inputKey,
        array &$blacklist
    ): DOMElement {
        $enc = new XMLSecEnc();

        $enc->setNode($encryptedData);
        $enc->type = $encryptedData->getAttribute("Type");

        $symmetricKey = $enc->locateKey($encryptedData);
        if (!$symmetricKey) {
            throw new Exception('Could not locate key algorithm in encrypted data.');
        }

        $symmetricKeyInfo = $enc->locateKeyInfo($symmetricKey);
        if (!$symmetricKeyInfo) {
            throw new Exception('Could not locate <dsig:KeyInfo> for the encrypted key.');
        }

        $inputKeyAlgo = $inputKey->getAlgorithm();
        if ($symmetricKeyInfo->isEncrypted) {
            $symKeyInfoAlgo = $symmetricKeyInfo->getAlgorithm();

            if (in_array($symKeyInfoAlgo, $blacklist, true)) {
                throw new Exception('Algorithm disabled: ' . var_export($symKeyInfoAlgo, true));
            }

            if ($symKeyInfoAlgo === XMLSecurityKey::RSA_OAEP_MGF1P && $inputKeyAlgo === XMLSecurityKey::RSA_1_5) {
                /*
                 * The RSA key formats are equal, so loading an RSA_1_5 key
                 * into an RSA_OAEP_MGF1P key can be done without problems.
                 * We therefore pretend that the input key is an
                 * RSA_OAEP_MGF1P key.
                 */
                $inputKeyAlgo = XMLSecurityKey::RSA_OAEP_MGF1P;
            }

            /* Make sure that the input key format is the same as the one used to encrypt the key. */
            if ($inputKeyAlgo !== $symKeyInfoAlgo) {
                throw new Exception(
                    'Algorithm mismatch between input key and key used to encrypt ' .
                    ' the symmetric key for the message. Key was: ' .
                    var_export($inputKeyAlgo, true) . '; message was: ' .
                    var_export($symKeyInfoAlgo, true)
                );
            }

            /** @var XMLSecEnc $encKey */
            $encKey = $symmetricKeyInfo->encryptedCtx;
            $symmetricKeyInfo->key = $inputKey->key;

            $keySize = $symmetricKey->getSymmetricKeySize();
            if ($keySize === null) {
                /* To protect against "key oracle" attacks, we need to be able to create a
                 * symmetric key, and for that we need to know the key size.
                 */
                throw new Exception(
                    'Unknown key size for encryption algorithm: ' . var_export($symmetricKey->type, true)
                );
            }

            try {
                /**
                 * @var string $key
                 * @psalm-suppress UndefinedClass
                 */
                $key = $encKey->decryptKey($symmetricKeyInfo);
                if (strlen($key) !== $keySize) {
                    throw new Exception(
                        'Unexpected key size (' . strval(strlen($key) * 8) . 'bits) for encryption algorithm: ' .
                        var_export($symmetricKey->type, true)
                    );
                }
            } catch (Exception $e) {
                /* We failed to decrypt this key. Log it, and substitute a "random" key. */
//                Utils::getContainer()->getLogger()->error('Failed to decrypt symmetric key: ' . $e->getMessage());
                /* Create a replacement key, so that it looks like we fail in the same way as if the key was correctly
                 * padded. */

                /* We base the symmetric key on the encrypted key and private key, so that we always behave the
                 * same way for a given input key.
                 */
                $encryptedKey = $encKey->getCipherValue();
                if ($encryptedKey === null) {
                    throw new Exception('No CipherValue available in the encrypted element.');
                }

                /** @psalm-suppress PossiblyNullArgument */
                $pkey = openssl_pkey_get_details($symmetricKeyInfo->key);
                $pkey = sha1(serialize($pkey), true);
                $key = sha1($encryptedKey . $pkey, true);

                /* Make sure that the key has the correct length. */
                if (strlen($key) > $keySize) {
                    $key = substr($key, 0, $keySize);
                } elseif (strlen($key) < $keySize) {
                    $key = str_pad($key, $keySize);
                }
            }
            $symmetricKey->loadkey($key);
        } else {
            $symKeyAlgo = $symmetricKey->getAlgorithm();
            /* Make sure that the input key has the correct format. */
            if ($inputKeyAlgo !== $symKeyAlgo) {
                throw new Exception(
                    'Algorithm mismatch between input key and key in message. ' .
                    'Key was: ' . var_export($inputKeyAlgo, true) . '; message was: ' .
                    var_export($symKeyAlgo, true)
                );
            }
            $symmetricKey = $inputKey;
        }

        $algorithm = $symmetricKey->getAlgorithm();
        if (in_array($algorithm, $blacklist, true)) {
            throw new Exception('Algorithm disabled: ' . var_export($algorithm, true));
        }

        /**
         * @var string $decrypted
         * @psalm-suppress UndefinedClass
         */
        $decrypted = $enc->decryptNode($symmetricKey, false);

        /*
         * This is a workaround for the case where only a subset of the XML
         * tree was serialized for encryption. In that case, we may miss the
         * namespaces needed to parse the XML.
         */
        $xml = '<root xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" ' .
                        'xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">' .
            $decrypted . '</root>';

        try {
            $newDoc = DOMDocumentFactory::fromString($xml);
        } catch (RuntimeException $e) {
            throw new Exception('Failed to parse decrypted XML. Maybe the wrong sharedkey was used?', 0, $e);
        }

        /** @psalm-suppress PossiblyNullPropertyFetch */
        $decryptedElement = $newDoc->firstChild->firstChild;
        if (!($decryptedElement instanceof DOMElement)) {
            throw new Exception('Missing decrypted element or it was not actually a DOMElement.');
        }

        return $decryptedElement;
    }