//Create S2 structure
DataStructs.SIGMA_S2_MESSAGE GenerateS2Structure()
{
DataStructs.SIGMA_S2_MESSAGE S2Message = new DataStructs.SIGMA_S2_MESSAGE();
//Fill the S2 fields
S2Message.Basename = new byte[DataStructs.BASE_NAME_LENGTH]; //The base name, chosen by the verifier, to be used in name based signatures. here you can use baseName, in case you want to do it.
S2Message.Gb = Gb; //The Verifier's ephemeral DH public key
S2Message.OcspReq = OCSPReq; //An (optional) OCSP Request from the prover
return(S2Message);
}
//Get S2 message
public bool GetS2Message(out byte[] S2MessageArray)
{
S2MessageArray = new byte[0];
byte[] cert = DataStructs.Sigma11_3PSignedCert; //Verifier's certificate
byte[] key = DataStructs.Sigma11_Signed3PKey; //Verifier's private key
//Get the OCSP response according to the request we've got from the proover
OCSPResp = GetOCSPResponseFromRealResponder(cert, OCSPReq.OcspNonce);
//if there is a problem with the OCSP server connection
if (OCSPResp == null)
{
return(false);
}
try
{
//Create S2 structure
DataStructs.SIGMA_S2_MESSAGE S2Message = GenerateS2Structure();
//Build the OCSP response
OCSPResp = BuildOCSPResp(cert, OCSPResp);
//Composing - Data contains Verifier Cert, SIG_RL_HEADER followed by Revocation List , OCSP Response (If requested) VLRs in this order. SigRL is optional.
List <byte> VerifierCertAndOCSPRespList = new List <byte>();
//Generate X509 verifier certificate
byte[] x509VerifierCertArray = GenerateX509VerifierCert(cert);
//Add the x509VerifierCert to S2 message
VerifierCertAndOCSPRespList.AddRange(x509VerifierCertArray);
//Here you can generate SIG-RL in case you want to use it, and add it to s2List
//Add the OCSP response to S2 message
VerifierCertAndOCSPRespList.AddRange(OCSPResp);
//Convert VerifierCert and OCSPResp list to a byte array
byte[] VerifierCertAndOCSPResp = VerifierCertAndOCSPRespList.ToArray();
//Convert OCSP request from structure to a byte array
byte[] ocspReqArray = Utils.StructureToByteArray(S2Message.OcspReq);
//Preparing the HMAC
//Constructing HMAC data - Gb || Basename || OCSP Req || Verifier Cert || Sig-RL List || OCSPResp
byte[] dataForHmac = new byte[DataStructs.SIGMA_PUBLIC_KEY_LEN + DataStructs.BASE_NAME_LENGTH + DataStructs.INT_SIZE + DataStructs.OCSP_NONCE_LENGTH + VerifierCertAndOCSPResp.Length];
S2Message.Gb.CopyTo(dataForHmac, 0);
S2Message.Basename.CopyTo(dataForHmac, DataStructs.SIGMA_PUBLIC_KEY_LEN);
ocspReqArray.CopyTo(dataForHmac, DataStructs.SIGMA_PUBLIC_KEY_LEN + DataStructs.BASE_NAME_LENGTH);
VerifierCertAndOCSPResp.CopyTo(dataForHmac, DataStructs.SIGMA_PUBLIC_KEY_LEN + DataStructs.BASE_NAME_LENGTH + DataStructs.INT_SIZE + DataStructs.OCSP_NONCE_LENGTH);
//Create HMAC - HMAC_SHA256 of [Gb || Basename || OCSP Req || Verifier Cert || Sig-RL List ], using SMK
CdgStatus status;
S2Message.S2Icv = new byte[DataStructs.SIGMA_MAC_LEN];
status = CryptoDataGenWrapper_1_1.CreateHmac(dataForHmac, dataForHmac.Length, SMK, DataStructs.SIGMA_SMK_LENGTH, S2Message.S2Icv, DataStructs.SIGMA_HMAC_LENGTH);
if (status != CdgStatus.CdgStsOk)
{
return(false);
}
//Create Signed [Ga || Gb] using verifier ECDSA public key
S2Message.SigGaGb = new byte[DataStructs.ECDSA_SIGNATURE_LEN];
status = CryptoDataGenWrapper_1_1.MessageSign(key, key.Length, GaGb, DataStructs.SIGMA_KEY_LENGTH * 2, S2Message.SigGaGb, DataStructs.ECDSA_SIGNATURE_LEN);
if (status != CdgStatus.CdgStsOk)
{
return(false);
}
//Prepare final S2 message array contains S2 message structure + verifier cert + OCSP response
int s2MessageLen = Marshal.SizeOf(S2Message);
S2MessageArray = new byte[s2MessageLen + VerifierCertAndOCSPResp.Length];
Utils.StructureToByteArray(S2Message).CopyTo(S2MessageArray, 0);
VerifierCertAndOCSPResp.CopyTo(S2MessageArray, s2MessageLen);
return(true);
}
catch (Exception e)
{
return(false);
}
}