WebAuthnRegistrationEvent::validateAttestationFormatApple()

Complexity

Conditions	15
Paths	640

Size

Total Lines	120
Code Lines	66

Duplication

Lines	0
Ratio	0 %

Importance

Changes	7
Bugs	1	Features	0

<?php
    private function validateAttestationFormatApple(array $attestationArray): void
    {
        // found at: https://www.apple.com/certificateauthority/private/

        $APPLE_WEBAUTHN_ROOT_CA = "-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----";
        // § 8.8 Bullet 1 of the draft spec at
        // https://pr-preview.s3.amazonaws.com/alanwaketan/webauthn/pull/1491.html#sctn-apple-anonymous-attestation
        // draft implemented in state of 11 Feb 2021
        // I can't help but notice that the verification procedure does NOTHING with CA certs from the chain,
        // nor is there a root to validate to!
        // Found the root CA with Google, see above, and will perform chain validation even if the spec doesn't say so.
        // first, clear the openssl error backlog. We might need error data in case things go sideways.
        while (openssl_error_string() !== false);

        $stmtDecoded = $attestationArray['attStmt'];
        if (!isset($stmtDecoded['x5c'])) {
            $this->fail("Apple attestation statement does not contain an x5c attestation statement!");
        }
        // § 8.8 Bullet 2
        $nonceToHash = $attestationArray['authData'] . $this->clientDataHash;
        // § 8.8 Bullet 3
        $cryptoUtils = new Utils\Crypto();
        $nonce = hash("sha256", $nonceToHash, true); // does raw_output have to be FALSE or TRUE?
        $certProps = openssl_x509_parse($cryptoUtils->der2pem($stmtDecoded['x5c'][0]));
        // § 8.8 Bullet 4
        if (
                !isset($certProps['extensions']['1.2.840.113635.100.8.2']) ||
                empty($certProps['extensions']['1.2.840.113635.100.8.2'])
        ) {
            $this->fail("The required nonce value is not present in the OID.");
        }
        $toCompare = substr($certProps['extensions']['1.2.840.113635.100.8.2'], 6);
        if ($nonce != $toCompare) {
            $this->fail("There is a mismatch between the nonce and the OID (XXX $nonce XXX , XXX $toCompare XXX ).");
        }

        // chain validation first
        foreach ($stmtDecoded['x5c'] as $runIndex => $runCert) {
            if (isset($stmtDecoded['x5c'][$runIndex + 1])) { // there is a next cert, so follow the chain
                $certResource = openssl_x509_read($cryptoUtils->der2pem($runCert));
                $signerPubKey = openssl_pkey_get_public($cryptoUtils->der2pem($stmtDecoded['x5c'][$runIndex + 1]));
                if (openssl_x509_verify($certResource, $signerPubKey) != 1) {
                    // phpcs:ignore Generic.Files.LineLength.TooLong
                    $this->fail("Error during chain validation of the attestation certificate (while validating cert #$runIndex, which is "
                            . $cryptoUtils->der2pem($runCert)
                            . "; next cert was "
                            . $cryptoUtils->der2pem($stmtDecoded['x5c'][$runIndex + 1]));
                }
            } else { // last cert, compare to the root
                $certResource = openssl_x509_read($cryptoUtils->der2pem($runCert));
                $signerPubKey = openssl_pkey_get_public($APPLE_WEBAUTHN_ROOT_CA);
                if (openssl_x509_verify($certResource, $signerPubKey) != 1) {
                    $this->fail(sprintf(
                        "Error during root CA validation of the attestation chain certificate, which is %s",
                        $cryptoUtils->der2pem($runCert),
                    ));
                }
            }
        }

        $keyResource = openssl_pkey_get_public($cryptoUtils->der2pem($stmtDecoded['x5c'][0]));
        if ($keyResource === false) {
            $this->fail(
            // phpcs:ignore Generic.Files.LineLength.TooLong
                "Did not get a parseable X.509 structure out of the Apple attestation statement - x5c nr. 0 statement was: XXX "
                . $stmtDecoded['x5c'][0]
                . " XXX; PEM equivalent is "
                . $cryptoUtils->der2pem($stmtDecoded['x5c'][0])
                . ". OpenSSL error: "
                . openssl_error_string(),
            );
        }

        // $this->credential is a public key in CBOR, not "PEM". We need to convert it first.
        $keyArray = $this->cborDecode(hex2bin($this->credential));
        $keyObject = new Ec2Key($keyArray);
        $credentialResource = openssl_pkey_get_public($keyObject->asPEM());

        if ($credentialResource === false) {
            $this->fail(
                "Could not create a public key from CBOR credential. XXX "
                . $this->credential
                . " XXX; PEM equivalent is "
                . $keyObject->asPEM()
                . ". OpenSSL error: "
                . openssl_error_string(),
            );
        }

        // § 8.8 Bullet 5
        $credentialDetails = openssl_pkey_get_details($credentialResource);
        $keyDetails = openssl_pkey_get_details($keyResource);
        if (
            $credentialDetails['bits'] != $keyDetails['bits'] ||
            $credentialDetails['key'] != $keyDetails['key'] ||
            $credentialDetails['type'] != $keyDetails['type']
        ) {
            $this->fail(
                "The credential public key does not match the certificate public key in attestationData. ("
                . $credentialDetails['key']
                . " - "
                . $keyDetails['key']
                . ")",
            );
        }
        $this->pass("Apple attestation format verification passed.");
        return;
    }