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<?php
namespace lbuchs\WebAuthn\Attestation;
use lbuchs\WebAuthn\WebAuthnException;
use lbuchs\WebAuthn\CBOR\CborDecoder;
use lbuchs\WebAuthn\Binary\ByteBuffer;
/**
* @author Lukas Buchs
* @license https://github.com/lbuchs/WebAuthn/blob/master/LICENSE MIT
*/
class AuthenticatorData {
protected $_binary;
protected $_rpIdHash;
protected $_flags;
protected $_signCount;
protected $_attestedCredentialData;
protected $_extensionData;
// Cose encoded keys
private static $_COSE_KTY = 1;
private static $_COSE_ALG = 3;
// Cose curve
private static $_COSE_CRV = -1;
private static $_COSE_X = -2;
private static $_COSE_Y = -3;
// Cose RSA PS256
private static $_COSE_N = -1;
private static $_COSE_E = -2;
// EC2 key type
private static $_EC2_TYPE = 2;
private static $_EC2_ES256 = -7;
private static $_EC2_P256 = 1;
// RSA key type
private static $_RSA_TYPE = 3;
private static $_RSA_RS256 = -257;
// OKP key type
private static $_OKP_TYPE = 1;
private static $_OKP_ED25519 = 6;
private static $_OKP_EDDSA = -8;
/**
* Parsing the authenticatorData binary.
* @param string $binary
* @throws WebAuthnException
*/
public function __construct($binary) {
if (!\is_string($binary) || \strlen($binary) < 37) {
throw new WebAuthnException('Invalid authenticatorData input', WebAuthnException::INVALID_DATA);
}
$this->_binary = $binary;
// Read infos from binary
// https://www.w3.org/TR/webauthn/#sec-authenticator-data
// RP ID
$this->_rpIdHash = \substr($binary, 0, 32);
// flags (1 byte)
$flags = \unpack('Cflags', \substr($binary, 32, 1))['flags'];
$this->_flags = $this->_readFlags($flags);
// signature counter: 32-bit unsigned big-endian integer.
$this->_signCount = \unpack('Nsigncount', \substr($binary, 33, 4))['signcount'];
$offset = 37;
// https://www.w3.org/TR/webauthn/#sec-attested-credential-data
if ($this->_flags->attestedDataIncluded) {
$this->_attestedCredentialData = $this->_readAttestData($binary, $offset);
}
if ($this->_flags->extensionDataIncluded) {
$this->_readExtensionData(\substr($binary, $offset));
}
}
/**
* Authenticator Attestation Globally Unique Identifier, a unique number
* that identifies the model of the authenticator (not the specific instance
* of the authenticator)
* The aaguid may be 0 if the user is using a old u2f device and/or if
* the browser is using the fido-u2f format.
* @return string
* @throws WebAuthnException
*/
public function getAAGUID() {
if (!($this->_attestedCredentialData instanceof \stdClass)) {
throw new WebAuthnException('credential data not included in authenticator data', WebAuthnException::INVALID_DATA);
}
return $this->_attestedCredentialData->aaguid;
}
/**
* returns the authenticatorData as binary
* @return string
*/
public function getBinary() {
return $this->_binary;
}
/**
* returns the credentialId
* @return string
* @throws WebAuthnException
*/
public function getCredentialId() {
if (!($this->_attestedCredentialData instanceof \stdClass)) {
throw new WebAuthnException('credential id not included in authenticator data', WebAuthnException::INVALID_DATA);
}
return $this->_attestedCredentialData->credentialId;
}
/**
* returns the public key in PEM format
* @return string
*/
public function getPublicKeyPem() {
if (!($this->_attestedCredentialData instanceof \stdClass) || !isset($this->_attestedCredentialData->credentialPublicKey)) {
throw new WebAuthnException('credential data not included in authenticator data', WebAuthnException::INVALID_DATA);
}
$der = null;
switch ($this->_attestedCredentialData->credentialPublicKey->kty ?? null) {
case self::$_EC2_TYPE: $der = $this->_getEc2Der(); break;
case self::$_RSA_TYPE: $der = $this->_getRsaDer(); break;
case self::$_OKP_TYPE: $der = $this->_getOkpDer(); break;
default: throw new WebAuthnException('invalid key type', WebAuthnException::INVALID_DATA);
}
$pem = '-----BEGIN PUBLIC KEY-----' . "\n";
$pem .= \chunk_split(\base64_encode($der), 64, "\n");
$pem .= '-----END PUBLIC KEY-----' . "\n";
return $pem;
}
/**
* returns the public key in U2F format
* @return string
* @throws WebAuthnException
*/
public function getPublicKeyU2F() {
if (!($this->_attestedCredentialData instanceof \stdClass) || !isset($this->_attestedCredentialData->credentialPublicKey)) {
throw new WebAuthnException('credential data not included in authenticator data', WebAuthnException::INVALID_DATA);
}
if (($this->_attestedCredentialData->credentialPublicKey->kty ?? null) !== self::$_EC2_TYPE) {
throw new WebAuthnException('signature algorithm not ES256', WebAuthnException::INVALID_PUBLIC_KEY);
}
return "\x04" . // ECC uncompressed
$this->_attestedCredentialData->credentialPublicKey->x .
$this->_attestedCredentialData->credentialPublicKey->y;
}
/**
* returns the SHA256 hash of the relying party id (=hostname)
* @return string
*/
public function getRpIdHash() {
return $this->_rpIdHash;
}
/**
* returns the sign counter
* @return int
*/
public function getSignCount() {
return $this->_signCount;
}
/**
* returns true if the user is present
* @return boolean
*/
public function getUserPresent() {
return $this->_flags->userPresent;
}
/**
* returns true if the user is verified
* @return boolean
*/
public function getUserVerified() {
return $this->_flags->userVerified;
}
// -----------------------------------------------
// PRIVATE
// -----------------------------------------------
/**
* Returns DER encoded EC2 key
* @return string
*/
private function _getEc2Der() {
return $this->_der_sequence(
$this->_der_sequence(
$this->_der_oid("\x2A\x86\x48\xCE\x3D\x02\x01") . // OID 1.2.840.10045.2.1 ecPublicKey
$this->_der_oid("\x2A\x86\x48\xCE\x3D\x03\x01\x07") // 1.2.840.10045.3.1.7 prime256v1
) .
$this->_der_bitString($this->getPublicKeyU2F())
);
}
/**
* Returns DER encoded EdDSA key
* @return string
*/
private function _getOkpDer() {
return $this->_der_sequence(
$this->_der_sequence(
$this->_der_oid("\x2B\x65\x70") // OID 1.3.101.112 curveEd25519 (EdDSA 25519 signature algorithm)
) .
$this->_der_bitString($this->_attestedCredentialData->credentialPublicKey->x)
);
}
/**
* Returns DER encoded RSA key
* @return string
*/
private function _getRsaDer() {
return $this->_der_sequence(
$this->_der_sequence(
$this->_der_oid("\x2A\x86\x48\x86\xF7\x0D\x01\x01\x01") . // OID 1.2.840.113549.1.1.1 rsaEncryption
$this->_der_nullValue()
) .
$this->_der_bitString(
$this->_der_sequence(
$this->_der_unsignedInteger($this->_attestedCredentialData->credentialPublicKey->n) .
$this->_der_unsignedInteger($this->_attestedCredentialData->credentialPublicKey->e)
)
)
);
}
/**
* reads the flags from flag byte
* @param string $binFlag
* @return \stdClass
*/
private function _readFlags($binFlag) {
$flags = new \stdClass();
$flags->bit_0 = !!($binFlag & 1);
$flags->bit_1 = !!($binFlag & 2);
$flags->bit_2 = !!($binFlag & 4);
$flags->bit_3 = !!($binFlag & 8);
$flags->bit_4 = !!($binFlag & 16);
$flags->bit_5 = !!($binFlag & 32);
$flags->bit_6 = !!($binFlag & 64);
$flags->bit_7 = !!($binFlag & 128);
// named flags
$flags->userPresent = $flags->bit_0;
$flags->userVerified = $flags->bit_2;
$flags->attestedDataIncluded = $flags->bit_6;
$flags->extensionDataIncluded = $flags->bit_7;
return $flags;
}
/**
* read attested data
* @param string $binary
* @param int $endOffset
* @return \stdClass
* @throws WebAuthnException
*/
private function _readAttestData($binary, &$endOffset) {
$attestedCData = new \stdClass();
if (\strlen($binary) <= 55) {
throw new WebAuthnException('Attested data should be present but is missing', WebAuthnException::INVALID_DATA);
}
// The AAGUID of the authenticator
$attestedCData->aaguid = \substr($binary, 37, 16);
//Byte length L of Credential ID, 16-bit unsigned big-endian integer.
$length = \unpack('nlength', \substr($binary, 53, 2))['length'];
$attestedCData->credentialId = \substr($binary, 55, $length);
// set end offset
$endOffset = 55 + $length;
// extract public key
$attestedCData->credentialPublicKey = $this->_readCredentialPublicKey($binary, 55 + $length, $endOffset);
return $attestedCData;
}
/**
* reads COSE key-encoded elliptic curve public key in EC2 format
* @param string $binary
* @param int $endOffset
* @return \stdClass
* @throws WebAuthnException
*/
private function _readCredentialPublicKey($binary, $offset, &$endOffset) {
$enc = CborDecoder::decodeInPlace($binary, $offset, $endOffset);
// COSE key-encoded elliptic curve public key in EC2 format
$credPKey = new \stdClass();
$credPKey->kty = $enc[self::$_COSE_KTY];
$credPKey->alg = $enc[self::$_COSE_ALG];
switch ($credPKey->alg) {
case self::$_EC2_ES256: $this->_readCredentialPublicKeyES256($credPKey, $enc); break;
case self::$_RSA_RS256: $this->_readCredentialPublicKeyRS256($credPKey, $enc); break;
case self::$_OKP_EDDSA: $this->_readCredentialPublicKeyEDDSA($credPKey, $enc); break;
}
return $credPKey;
}
/**
* extract EDDSA informations from cose
* @param \stdClass $credPKey
* @param \stdClass $enc
* @throws WebAuthnException
*/
private function _readCredentialPublicKeyEDDSA(&$credPKey, $enc) {
$credPKey->crv = $enc[self::$_COSE_CRV];
$credPKey->x = $enc[self::$_COSE_X] instanceof ByteBuffer ? $enc[self::$_COSE_X]->getBinaryString() : null;
unset ($enc);
// Validation
if ($credPKey->kty !== self::$_OKP_TYPE) {
throw new WebAuthnException('public key not in OKP format', WebAuthnException::INVALID_PUBLIC_KEY);
}
if ($credPKey->alg !== self::$_OKP_EDDSA) {
throw new WebAuthnException('signature algorithm not EdDSA', WebAuthnException::INVALID_PUBLIC_KEY);
}
if ($credPKey->crv !== self::$_OKP_ED25519) {
throw new WebAuthnException('curve not Ed25519', WebAuthnException::INVALID_PUBLIC_KEY);
}
if (\strlen($credPKey->x) !== 32) {
throw new WebAuthnException('Invalid X-coordinate', WebAuthnException::INVALID_PUBLIC_KEY);
}
}
/**
* extract ES256 informations from cose
* @param \stdClass $credPKey
* @param \stdClass $enc
* @throws WebAuthnException
*/
private function _readCredentialPublicKeyES256(&$credPKey, $enc) {
$credPKey->crv = $enc[self::$_COSE_CRV];
$credPKey->x = $enc[self::$_COSE_X] instanceof ByteBuffer ? $enc[self::$_COSE_X]->getBinaryString() : null;
$credPKey->y = $enc[self::$_COSE_Y] instanceof ByteBuffer ? $enc[self::$_COSE_Y]->getBinaryString() : null;
unset ($enc);
// Validation
if ($credPKey->kty !== self::$_EC2_TYPE) {
throw new WebAuthnException('public key not in EC2 format', WebAuthnException::INVALID_PUBLIC_KEY);
}
if ($credPKey->alg !== self::$_EC2_ES256) {
throw new WebAuthnException('signature algorithm not ES256', WebAuthnException::INVALID_PUBLIC_KEY);
}
if ($credPKey->crv !== self::$_EC2_P256) {
throw new WebAuthnException('curve not P-256', WebAuthnException::INVALID_PUBLIC_KEY);
}
if (\strlen($credPKey->x) !== 32) {
throw new WebAuthnException('Invalid X-coordinate', WebAuthnException::INVALID_PUBLIC_KEY);
}
if (\strlen($credPKey->y) !== 32) {
throw new WebAuthnException('Invalid Y-coordinate', WebAuthnException::INVALID_PUBLIC_KEY);
}
}
/**
* extract RS256 informations from COSE
* @param \stdClass $credPKey
* @param \stdClass $enc
* @throws WebAuthnException
*/
private function _readCredentialPublicKeyRS256(&$credPKey, $enc) {
$credPKey->n = $enc[self::$_COSE_N] instanceof ByteBuffer ? $enc[self::$_COSE_N]->getBinaryString() : null;
$credPKey->e = $enc[self::$_COSE_E] instanceof ByteBuffer ? $enc[self::$_COSE_E]->getBinaryString() : null;
unset ($enc);
// Validation
if ($credPKey->kty !== self::$_RSA_TYPE) {
throw new WebAuthnException('public key not in RSA format', WebAuthnException::INVALID_PUBLIC_KEY);
}
if ($credPKey->alg !== self::$_RSA_RS256) {
throw new WebAuthnException('signature algorithm not ES256', WebAuthnException::INVALID_PUBLIC_KEY);
}
if (\strlen($credPKey->n) !== 256) {
throw new WebAuthnException('Invalid RSA modulus', WebAuthnException::INVALID_PUBLIC_KEY);
}
if (\strlen($credPKey->e) !== 3) {
throw new WebAuthnException('Invalid RSA public exponent', WebAuthnException::INVALID_PUBLIC_KEY);
}
}
/**
* reads cbor encoded extension data.
* @param string $binary
* @return array
* @throws WebAuthnException
*/
private function _readExtensionData($binary) {
$ext = CborDecoder::decode($binary);
if (!\is_array($ext)) {
throw new WebAuthnException('invalid extension data', WebAuthnException::INVALID_DATA);
}
return $ext;
}
// ---------------
// DER functions
// ---------------
private function _der_length($len) {
if ($len < 128) {
return \chr($len);
}
$lenBytes = '';
while ($len > 0) {
$lenBytes = \chr($len % 256) . $lenBytes;
$len = \intdiv($len, 256);
}
return \chr(0x80 | \strlen($lenBytes)) . $lenBytes;
}
private function _der_sequence($contents) {
return "\x30" . $this->_der_length(\strlen($contents)) . $contents;
}
private function _der_oid($encoded) {
return "\x06" . $this->_der_length(\strlen($encoded)) . $encoded;
}
private function _der_bitString($bytes) {
return "\x03" . $this->_der_length(\strlen($bytes) + 1) . "\x00" . $bytes;
}
private function _der_nullValue() {
return "\x05\x00";
}
private function _der_unsignedInteger($bytes) {
$len = \strlen($bytes);
// Remove leading zero bytes
for ($i = 0; $i < ($len - 1); $i++) {
if (\ord($bytes[$i]) !== 0) {
break;
}
}
if ($i !== 0) {
$bytes = \substr($bytes, $i);
}
// If most significant bit is set, prefix with another zero to prevent it being seen as negative number
if ((\ord($bytes[0]) & 0x80) !== 0) {
$bytes = "\x00" . $bytes;
}
return "\x02" . $this->_der_length(\strlen($bytes)) . $bytes;
}
}