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); }
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 (null == Sig || CBORType.ByteString != Sig.Type || 0 == Sig.GetByteString().Length) { throw new Fido2VerificationException("Invalid TPM attestation signature"); } if ("2.0" != attStmt["ver"].AsString()) { throw new Fido2VerificationException("FIDO2 only supports TPM 2.0"); } // 2. Verify that the public key specified by the parameters and unique fields of pubArea // is identical to the credentialPublicKey in the attestedCredentialData in authenticatorData PubArea pubArea = null; if (null != attStmt["pubArea"] && CBORType.ByteString == attStmt["pubArea"].Type && 0 != attStmt["pubArea"].GetByteString().Length) { pubArea = new PubArea(attStmt["pubArea"].GetByteString()); } if (null == pubArea || null == pubArea.Unique || 0 == pubArea.Unique.Length) { throw new Fido2VerificationException("Missing or malformed pubArea"); } var coseKty = CredentialPublicKey[CBORObject.FromObject(COSE.KeyCommonParameter.KeyType)].AsInt32(); if (3 == coseKty) // RSA { var coseMod = CredentialPublicKey[CBORObject.FromObject(COSE.KeyTypeParameter.N)].GetByteString(); // modulus var coseExp = CredentialPublicKey[CBORObject.FromObject(COSE.KeyTypeParameter.E)].GetByteString(); // exponent if (!coseMod.ToArray().SequenceEqual(pubArea.Unique.ToArray())) { throw new Fido2VerificationException("Public key mismatch between pubArea and credentialPublicKey"); } if ((coseExp[0] + (coseExp[1] << 8) + (coseExp[2] << 16)) != pubArea.Exponent) { throw new Fido2VerificationException("Public key exponent mismatch between pubArea and credentialPublicKey"); } } else if (2 == coseKty) // ECC { var curve = CredentialPublicKey[CBORObject.FromObject(COSE.KeyTypeParameter.Crv)].AsInt32(); var X = CredentialPublicKey[CBORObject.FromObject(COSE.KeyTypeParameter.X)].GetByteString(); var Y = CredentialPublicKey[CBORObject.FromObject(COSE.KeyTypeParameter.Y)].GetByteString(); if (pubArea.EccCurve != CoseCurveToTpm[curve]) { throw new Fido2VerificationException("Curve mismatch between pubArea and credentialPublicKey"); } if (!pubArea.ECPoint.X.SequenceEqual(X)) { throw new Fido2VerificationException("X-coordinate mismatch between pubArea and credentialPublicKey"); } if (!pubArea.ECPoint.Y.SequenceEqual(Y)) { throw new Fido2VerificationException("Y-coordinate mismatch between pubArea and credentialPublicKey"); } } // 3. Concatenate authenticatorData and clientDataHash to form attToBeSigned // See Data field of base class // 4. Validate that certInfo is valid CertInfo certInfo = null; if (null != attStmt["certInfo"] && CBORType.ByteString == attStmt["certInfo"].Type && 0 != attStmt["certInfo"].GetByteString().Length) { certInfo = new CertInfo(attStmt["certInfo"].GetByteString()); } if (null == certInfo) { throw new Fido2VerificationException("CertInfo invalid parsing TPM format attStmt"); } // 4a. Verify that magic is set to TPM_GENERATED_VALUE // Handled in CertInfo constructor, see CertInfo.Magic // 4b. Verify that type is set to TPM_ST_ATTEST_CERTIFY // Handled in CertInfo constructor, see CertInfo.Type // 4c. Verify that extraData is set to the hash of attToBeSigned using the hash algorithm employed in "alg" if (null == Alg || true != Alg.IsNumber) { throw new Fido2VerificationException("Invalid TPM attestation algorithm"); } using (var hasher = CryptoUtils.GetHasher(CryptoUtils.HashAlgFromCOSEAlg(Alg.AsInt32()))) { if (!hasher.ComputeHash(Data).SequenceEqual(certInfo.ExtraData)) { throw new Fido2VerificationException("Hash value mismatch extraData and attToBeSigned"); } } // 4d. Verify that attested contains a TPMS_CERTIFY_INFO structure, whose name field contains a valid Name for pubArea, as computed using the algorithm in the nameAlg field of pubArea using (var hasher = CryptoUtils.GetHasher(CryptoUtils.HashAlgFromCOSEAlg(certInfo.Alg))) { if (false == hasher.ComputeHash(pubArea.Raw).SequenceEqual(certInfo.AttestedName)) { throw new Fido2VerificationException("Hash value mismatch attested and pubArea"); } } // 4e. Note that the remaining fields in the "Standard Attestation Structure" [TPMv2-Part1] section 31.2, i.e., qualifiedSigner, clockInfo and firmwareVersion are ignored. These fields MAY be used as an input to risk engines. // 5. If x5c is present, this indicates that the attestation type is not ECDAA if (null != X5c && CBORType.Array == X5c.Type && 0 != X5c.Count) { 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 TPM attestation"); } // 5a. Verify the sig is a valid signature over certInfo using the attestation public key in aikCert with the algorithm specified in alg. var aikCert = new X509Certificate2(X5c.Values.First().GetByteString()); var cpk = new CredentialPublicKey(aikCert, Alg.AsInt32()); if (true != cpk.Verify(certInfo.Raw, Sig.GetByteString())) { throw new Fido2VerificationException("Bad signature in TPM with aikCert"); } // 5b. Verify that aikCert meets the TPM attestation statement certificate requirements // https://www.w3.org/TR/webauthn/#tpm-cert-requirements // 5bi. Version MUST be set to 3 if (3 != aikCert.Version) { throw new Fido2VerificationException("aikCert must be V3"); } // 5bii. Subject field MUST be set to empty - they actually mean subject name if (0 != aikCert.SubjectName.Name.Length) { throw new Fido2VerificationException("aikCert subject must be empty"); } // 5biii. The Subject Alternative Name extension MUST be set as defined in [TPMv2-EK-Profile] section 3.2.9. // https://www.w3.org/TR/webauthn/#tpm-cert-requirements (string tpmManufacturer, string tpmModel, string tpmVersion) = SANFromAttnCertExts(aikCert.Extensions); // From https://www.trustedcomputinggroup.org/wp-content/uploads/Credential_Profile_EK_V2.0_R14_published.pdf // "The issuer MUST include TPM manufacturer, TPM part number and TPM firmware version, using the directoryName // form within the GeneralName structure. The ASN.1 encoding is specified in section 3.1.2 TPM Device // Attributes. In accordance with RFC 5280[11], this extension MUST be critical if subject is empty // and SHOULD be non-critical if subject is non-empty" // Best I can figure to do for now? if (string.Empty == tpmManufacturer || string.Empty == tpmModel || string.Empty == tpmVersion) { throw new Fido2VerificationException("SAN missing TPMManufacturer, TPMModel, or TPMVersion from TPM attestation certificate"); } if (false == TPMManufacturers.Contains(tpmManufacturer)) { throw new Fido2VerificationException("Invalid TPM manufacturer found parsing TPM attestation"); } // 5biiii. The Extended Key Usage extension MUST contain the "joint-iso-itu-t(2) internationalorganizations(23) 133 tcg-kp(8) tcg-kp-AIKCertificate(3)" OID. // OID is 2.23.133.8.3 var EKU = EKUFromAttnCertExts(aikCert.Extensions, "2.23.133.8.3"); if (!EKU) { throw new Fido2VerificationException("aikCert EKU missing tcg-kp-AIKCertificate OID"); } // 5biiiii. The Basic Constraints extension MUST have the CA component set to false. if (IsAttnCertCACert(aikCert.Extensions)) { throw new Fido2VerificationException("aikCert Basic Constraints extension CA component must be false"); } // 5biiiiii. An Authority Information Access (AIA) extension with entry id-ad-ocsp and a CRL Distribution Point extension [RFC5280] // are both OPTIONAL as the status of many attestation certificates is available through metadata services. See, for example, the FIDO Metadata Service [FIDOMetadataService]. var trustPath = X5c.Values .Select(x => new X509Certificate2(x.GetByteString())) .ToArray(); // 5c. If aikCert contains an extension with OID 1.3.6.1.4.1.45724.1.1.4 (id-fido-gen-ce-aaguid) verify that the value of this extension matches the aaguid in authenticatorData var aaguid = AaguidFromAttnCertExts(aikCert.Extensions); if ((null != aaguid) && (!aaguid.SequenceEqual(Guid.Empty.ToByteArray())) && (0 != AttestedCredentialData.FromBigEndian(aaguid).CompareTo(AuthData.AttestedCredentialData.AaGuid))) { throw new Fido2VerificationException(string.Format("aaguid malformed, expected {0}, got {1}", AuthData.AttestedCredentialData.AaGuid, new Guid(aaguid))); } return(AttestationType.AttCa, trustPath); } // If ecdaaKeyId is present, then the attestation type is ECDAA else if (null != EcdaaKeyId) { // Perform ECDAA-Verify on sig to verify that it is a valid signature over certInfo // https://www.w3.org/TR/webauthn/#biblio-fidoecdaaalgorithm throw new Fido2VerificationException("ECDAA support for TPM attestation is not yet implemented"); // If successful, return attestation type ECDAA and the identifier of the ECDAA-Issuer public key ecdaaKeyId. //attnType = AttestationType.ECDAA; //trustPath = ecdaaKeyId; } else { throw new Fido2VerificationException("Neither x5c nor ECDAA were found in the TPM attestation statement"); } }