private bool VerifyS3Message(byte[] s3Message)
{
// Convert S3 message from byte array into the compatible structure
object S3MessageObj = new SigmaDataStructs.SigmaS3Message();
GeneralUtils.ByteArrayToStructure(s3Message, ref S3MessageObj);
SigmaDataStructs.SigmaS3Message S3Message = (SigmaDataStructs.SigmaS3Message)S3MessageObj;
// Locate the data index in the message
int dataInd = Marshal.SizeOf(typeof(SigmaDataStructs.SigmaS3Message)) - 1 + 32;
// Copy S3 message data from the received message into the S3 strucure data field
S3Message.data = new byte[s3Message.Length - dataInd];
Array.Copy(s3Message, dataInd, S3Message.data, 0, S3Message.data.Length);
// Prepare data for HMAC
byte[] dataForHmac = new byte[s3Message.Length - S3Message.S3Icv.Length];
Array.Copy(s3Message, S3Message.S3Icv.Length, dataForHmac, 0, dataForHmac.Length);
// Verify HMAC
CdgResult retStat = CdgResult.CdgValid;
CdgStatus status;
status = CryptoDataGenWrapper.VerifyHmac(dataForHmac, dataForHmac.Length, S3Message.S3Icv, SigmaDataStructs.SIGMA_MAC_LEN, SMK, SigmaDataStructs.SIGMA_SMK_LENGTH, ref retStat);
if (status != CdgStatus.CdgStsOk || retStat != CdgResult.CdgValid)
{
return(false);
}
// Check whether BK exists in the signed message, as a part of the S3 message validation
byte[] GaGbSig = new byte[SigmaDataStructs.EPID_SIG_LEN];
if (!SigmaUtils.DoesBKExist(S3Message, ref GaGbSig))
{
return(false);
}
// groupCert contains the SIGMA 1.0 certificate for the specific EPID group ID
byte[] groupCert = SigmaUtils.GetSpecificEpidCertificate_SIGMA_1_0(epidGroupID);
// epidParamsCert contains the mathematic parameters
byte[] epidParamsData = File.ReadAllBytes(EPIDDataStructs.PRODUCTION_SIGNED_BIN_PARAMS_CERT_FILE);
// Verify message. If a revocation list is used - the dll function will also check that the platform was not revoked.
status = CryptoDataGenWrapper.MessageVerifyPch(groupCert, groupCert.Length, epidParamsData, GaGb, GaGb.Length, null, 0, GaGbSig, GaGbSig.Length, out retStat, null);
if (status != CdgStatus.CdgStsOk || retStat != CdgResult.CdgValid)
{
return(false);
}
return(true);
}
private CdgStatus ProcessS1Message(byte[] s1Msg)
{
// Convert S1 message from byte array into the compatible structure
object s1Message = new SigmaDataStructs.SigmaS1Message();
GeneralUtils.ByteArrayToStructure(s1Msg, ref s1Message);
// Extract S1 message
SigmaDataStructs.SigmaS1Message message = (SigmaDataStructs.SigmaS1Message)s1Message;
Ga = message.Ga; // Prover's ephemeral DH public key
OCSPReq = message.OcspReq; // An (optional) OCSP Request from the prover
epidGroupID = message.Gid; // Platform EPID group ID
// Derive SK (Session Confidentiality Key: 128 bit derived from SMK), MK(Session Integrity Key: 128bit derived from SMK) and SMK(Session Message Key)
byte[] Sk = new byte[SigmaDataStructs.SIGMA_SESSION_KEY_LEN];
byte[] Mk = new byte[SigmaDataStructs.SIGMA_MAC_KEY_LEN];
CdgStatus status = CryptoDataGenWrapper.DeriveSigmaKeys(Ga, Ga.Length, Gb, Gb.Length, Sk, Sk.Length, Mk, Mk.Length, SMK, SMK.Length);
return(status);
}