public override (AttestationType, X509Certificate2[]) Verify() { // verify that aaguid is 16 empty bytes (note: required by fido2 conformance testing, could not find this in spec?) if (0 != AuthData.AttestedCredentialData.AaGuid.CompareTo(Guid.Empty)) { throw new Fido2VerificationException("Aaguid was not empty parsing fido-u2f atttestation statement"); } // https://www.w3.org/TR/webauthn/#fido-u2f-attestation // 1. Verify that attStmt is valid CBOR conforming to the syntax defined above and perform CBOR decoding on it to extract the contained fields. // (handled in base class) if (null == X5c || CBORType.Array != X5c.Type || X5c.Count != 1) { throw new Fido2VerificationException("Malformed x5c in fido - u2f attestation"); } // 2a. Check that x5c has exactly one element and let attCert be that element. if (null == X5c.Values || 0 == X5c.Values.Count || CBORType.ByteString != X5c.Values.First().Type || 0 == X5c.Values.First().GetByteString().Length) { throw new Fido2VerificationException("Malformed x5c in fido-u2f attestation"); } var attCert = new X509Certificate2(X5c.Values.First().GetByteString()); // TODO : Check why this variable isn't used. Remove it or use it. var u2ftransports = U2FTransportsFromAttnCert(attCert.Extensions); // 2b. If certificate public key is not an Elliptic Curve (EC) public key over the P-256 curve, terminate this algorithm and return an appropriate error var pubKey = attCert.GetECDsaPublicKey(); var keyParams = pubKey.ExportParameters(false); if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows)) { if (!keyParams.Curve.Oid.FriendlyName.Equals(ECCurve.NamedCurves.nistP256.Oid.FriendlyName)) { throw new Fido2VerificationException("Attestation certificate public key is not an Elliptic Curve (EC) public key over the P-256 curve"); } } else { if (!keyParams.Curve.Oid.Value.Equals(ECCurve.NamedCurves.nistP256.Oid.Value)) { throw new Fido2VerificationException("Attestation certificate public key is not an Elliptic Curve (EC) public key over the P-256 curve"); } } // 3. Extract the claimed rpIdHash from authenticatorData, and the claimed credentialId and credentialPublicKey from authenticatorData // see rpIdHash, credentialId, and credentialPublicKey members of base class AuthenticatorData (AuthData) // 4. Convert the COSE_KEY formatted credentialPublicKey (see Section 7 of [RFC8152]) to CTAP1/U2F public Key format (Raw ANSI X9.62 public key format) // 4a. Let x be the value corresponding to the "-2" key (representing x coordinate) in credentialPublicKey, and confirm its size to be of 32 bytes. If size differs or "-2" key is not found, terminate this algorithm and return an appropriate error var x = CredentialPublicKey[CBORObject.FromObject(COSE.KeyTypeParameter.X)].GetByteString(); // 4b. Let y be the value corresponding to the "-3" key (representing y coordinate) in credentialPublicKey, and confirm its size to be of 32 bytes. If size differs or "-3" key is not found, terminate this algorithm and return an appropriate error var y = CredentialPublicKey[CBORObject.FromObject(COSE.KeyTypeParameter.Y)].GetByteString(); // 4c.Let publicKeyU2F be the concatenation 0x04 || x || y var publicKeyU2F = new byte[1] { 0x4 }.Concat(x).Concat(y).ToArray(); // 5. Let verificationData be the concatenation of (0x00 || rpIdHash || clientDataHash || credentialId || publicKeyU2F) var verificationData = new byte[1] { 0x00 }; verificationData = verificationData .Concat(AuthData.RpIdHash) .Concat(clientDataHash) .Concat(AuthData.AttestedCredentialData.CredentialID) .Concat(publicKeyU2F.ToArray()) .ToArray(); // 6. Verify the sig using verificationData and certificate public key if (null == Sig || CBORType.ByteString != Sig.Type || 0 == Sig.GetByteString().Length) { throw new Fido2VerificationException("Invalid fido-u2f attestation signature"); } byte[] ecsig; try { ecsig = CryptoUtils.SigFromEcDsaSig(Sig.GetByteString(), pubKey.KeySize); } catch (Exception ex) { throw new Fido2VerificationException("Failed to decode fido-u2f attestation signature from ASN.1 encoded form", ex); } var coseAlg = CredentialPublicKey[CBORObject.FromObject(COSE.KeyCommonParameter.Alg)].AsInt32(); var hashAlg = CryptoUtils.HashAlgFromCOSEAlg(coseAlg); if (true != pubKey.VerifyData(verificationData, ecsig, hashAlg)) { throw new Fido2VerificationException("Invalid fido-u2f attestation signature"); } // 7. Optionally, inspect x5c and consult externally provided knowledge to determine whether attStmt conveys a Basic or AttCA attestation var trustPath = X5c.Values .Select(x => new X509Certificate2(x.GetByteString())) .ToArray(); return(AttestationType.AttCa, trustPath); }
public override (AttestationType, X509Certificate2[]) Verify() { // 1. Verify that attStmt is valid CBOR conforming to the syntax defined above and perform CBOR decoding on it to extract the contained fields // (handled in base class) if (0 == attStmt.Keys.Count || 0 == attStmt.Values.Count) { throw new Fido2VerificationException("Attestation format android-key must have attestation statement"); } if (null == Sig || CBORType.ByteString != Sig.Type || 0 == Sig.GetByteString().Length) { throw new Fido2VerificationException("Invalid android-key attestation signature"); } // 2. Verify that sig is a valid signature over the concatenation of authenticatorData and clientDataHash // using the attestation public key in attestnCert with the algorithm specified in alg if (null == X5c || CBORType.Array != X5c.Type || 0 == X5c.Count) { throw new Fido2VerificationException("Malformed x5c in android-key attestation"); } if (null == X5c.Values || 0 == X5c.Values.Count || CBORType.ByteString != X5c.Values.First().Type || 0 == X5c.Values.First().GetByteString().Length) { throw new Fido2VerificationException("Malformed x5c in android-key attestation"); } X509Certificate2 androidKeyCert; ECDsa androidKeyPubKey; try { androidKeyCert = new X509Certificate2(X5c.Values.First().GetByteString()); androidKeyPubKey = androidKeyCert.GetECDsaPublicKey(); // attestation public key } catch (Exception ex) { throw new Fido2VerificationException("Failed to extract public key from android key: " + ex.Message, ex); } if (null == Alg || true != Alg.IsNumber) { throw new Fido2VerificationException("Invalid android key attestation algorithm"); } byte[] ecsig; try { ecsig = CryptoUtils.SigFromEcDsaSig(Sig.GetByteString(), androidKeyPubKey.KeySize); } catch (Exception ex) { throw new Fido2VerificationException("Failed to decode android key attestation signature from ASN.1 encoded form", ex); } if (true != androidKeyPubKey.VerifyData(Data, ecsig, CryptoUtils.HashAlgFromCOSEAlg(Alg.AsInt32()))) { throw new Fido2VerificationException("Invalid android key attestation signature"); } // 3. Verify that the public key in the first certificate in x5c matches the credentialPublicKey in the attestedCredentialData in authenticatorData. if (true != AuthData.AttestedCredentialData.CredentialPublicKey.Verify(Data, Sig.GetByteString())) { throw new Fido2VerificationException("Incorrect credentialPublicKey in android key attestation"); } // 4. Verify that the attestationChallenge field in the attestation certificate extension data is identical to clientDataHash var attExtBytes = AttestationExtensionBytes(androidKeyCert.Extensions); if (null == attExtBytes) { throw new Fido2VerificationException("Android key attestation certificate contains no AttestationRecord extension"); } try { var attestationChallenge = GetAttestationChallenge(attExtBytes); if (false == clientDataHash.SequenceEqual(attestationChallenge)) { throw new Fido2VerificationException("Mismatch between attestationChallenge and hashedClientDataJson verifying android key attestation certificate extension"); } } catch (Exception) { throw new Fido2VerificationException("Malformed android key AttestationRecord extension verifying android key attestation certificate extension"); } // 5. Verify the following using the appropriate authorization list from the attestation certificate extension data // 5a. The AuthorizationList.allApplications field is not present, since PublicKeyCredential MUST be bound to the RP ID if (true == FindAllApplicationsField(attExtBytes)) { throw new Fido2VerificationException("Found all applications field in android key attestation certificate extension"); } // 5bi. The value in the AuthorizationList.origin field is equal to KM_ORIGIN_GENERATED ( which == 0). if (false == IsOriginGenerated(attExtBytes)) { throw new Fido2VerificationException("Found origin field not set to KM_ORIGIN_GENERATED in android key attestation certificate extension"); } // 5bii. The value in the AuthorizationList.purpose field is equal to KM_PURPOSE_SIGN (which == 2). if (false == IsPurposeSign(attExtBytes)) { throw new Fido2VerificationException("Found purpose field not set to KM_PURPOSE_SIGN in android key attestation certificate extension"); } var trustPath = X5c.Values .Select(x => new X509Certificate2(x.GetByteString())) .ToArray(); return(AttestationType.Basic, trustPath); }