private AuthResponse AuthStep1(AuthRequest authRequest)
{
// first step never fails: User -> Host: I, A = g^a (identifies self, a = random number)
var userName = authRequest.GetUserName();
var clientEphemeralPublic = authRequest.GetClientPublicEphemeral();
var account = AuthRepository.FindByName(userName);
if (account != null)
{
// save the data for the second authentication step
var salt = account.Salt;
var verifier = account.Verifier;
var serverEphemeral = SrpServer.GenerateEphemeral(verifier);
PendingAuthentications[authRequest.GetLoginSession()] = new Step1Data
{
Account = account,
ClientEphemeralPublic = clientEphemeralPublic,
ServerEphemeral = serverEphemeral,
};
// Host -> User: s, B = kv + g^b (sends salt, b = random number)
return(ResponseStep1(salt, serverEphemeral.Public, authRequest.GetLoginSession()));
}
var fakeSalt = SrpParameters.Hash(userName + UnknownUserSalt).ToHex();
var fakeEphemeral = SrpServer.GenerateEphemeral(fakeSalt);
return(ResponseStep1(fakeSalt, fakeEphemeral.Public, authRequest.GetLoginSession()));
}
private AuthResponseMessage AuthStep1(AuthRequestMessage authRequest)
{
// first step never fails: User -> Host: I, A = g^a (identifies self, a = random number)
var userName = (string)authRequest.Credentials[SrpProtocolConstants.SRP_USERNAME];
var clientEphemeralPublic = (string)authRequest.Credentials[SrpProtocolConstants.SRP_CLIENT_PUBLIC_EPHEMERAL];
var account = AuthRepository.FindByName(userName);
if (account != null)
{
// save the data for the second authentication step
var salt = account.Salt;
var verifier = account.Verifier;
var serverEphemeral = SrpServer.GenerateEphemeral(verifier);
PendingAuthentications[authRequest.SessionID] = new Step1Data
{
Account = account,
ClientEphemeralPublic = clientEphemeralPublic,
ServerEphemeral = serverEphemeral
};
// Host -> User: s, B = kv + g^b (sends salt, b = random number)
return(ResponseStep1(salt, serverEphemeral.Public));
}
// generate fake salt and B values so that attacker cannot tell whether the given user exists or not
var fakeSalt = SrpParameters.Hash(userName + UnknownUserSalt).ToHex();
var fakeEphemeral = SrpServer.GenerateEphemeral(fakeSalt);
return(ResponseStep1(fakeSalt, fakeEphemeral.Public));
}