/// <summary>
/// Handles the registration response received from the coordinator.
/// </summary>
/// <remarks>
/// Verifies the registration response message proofs, creates the credentials based on the issued MACs and
/// finally updates the credentials pool by removing those credentials that were presented and by adding
/// those that were issued.
/// </remarks>
/// <param name="registrationResponse">The registration response message received from the coordinator.</param>
/// <param name="registrationValidationData">The state data required to validate the issued credentials and the proofs.</param>
public void HandleResponse(RegistrationResponseMessage registrationResponse, RegistrationValidationData registrationValidationData)
{
Guard.NotNull(nameof(registrationResponse), registrationResponse);
Guard.NotNull(nameof(registrationValidationData), registrationValidationData);
var issuedCredentialCount = registrationResponse.IssuedCredentials.Count();
var requestedCredentialCount = registrationValidationData.Requested.Count();
if (issuedCredentialCount != NumberOfCredentials)
{
throw new WabiSabiException(
WabiSabiErrorCode.IssuedCredentialNumberMismatch,
$"{issuedCredentialCount} issued but {requestedCredentialCount} were requested.");
}
var credentials = Enumerable
.Zip(registrationValidationData.Requested, registrationResponse.IssuedCredentials)
.Select(x => (Requested: x.First, Issued: x.Second))
.ToArray();
var statements = credentials
.Select(x => ProofSystem.IssuerParametersStatement(CoordinatorParameters, x.Issued, x.Requested.Ma));
var areCorrectlyIssued = ProofSystem.Verify(registrationValidationData.Transcript, statements, registrationResponse.Proofs);
if (!areCorrectlyIssued)
{
throw new WabiSabiException(WabiSabiErrorCode.ClientReceivedInvalidProofs);
}
var credentialReceived = credentials.Select(x =>
new Credential(new Scalar((ulong)x.Requested.Amount.Satoshi), x.Requested.Randomness, x.Issued));
Credentials.UpdateCredentials(credentialReceived, registrationValidationData.Presented);
}
/// <summary>
/// Process the <see cref="RegistrationRequestMessage">credentials registration requests</see> and
/// issues the credentials.
/// </summary>
/// <param name="registrationRequest">The request containing the credentials presentations, credential requests and the proofs.</param>
/// <returns>The <see cref="RegistrationResponseMessage">registration response</see> containing the requested credentials and the proofs.</returns>
/// <exception cref="WabiSabiException">Error code: <see cref="WabiSabiErrorCode">WabiSabiErrorCode</see></exception>
public RegistrationResponseMessage HandleRequest(RegistrationRequestMessage registrationRequest)
{
Guard.NotNull(nameof(registrationRequest), registrationRequest);
var requested = registrationRequest.Requested ?? Enumerable.Empty <IssuanceRequest>();
var presented = registrationRequest.Presented ?? Enumerable.Empty <CredentialPresentation>();
var requestedCount = requested.Count();
if (requestedCount != NumberOfCredentials)
{
throw new WabiSabiException(
WabiSabiErrorCode.InvalidNumberOfRequestedCredentials,
$"{NumberOfCredentials} credential requests were expected but {requestedCount} were received.");
}
var presentedCount = presented.Count();
var requiredNumberOfPresentations = registrationRequest.IsNullRequest ? 0 : NumberOfCredentials;
if (presentedCount != requiredNumberOfPresentations)
{
throw new WabiSabiException(
WabiSabiErrorCode.InvalidNumberOfPresentedCredentials,
$"{requiredNumberOfPresentations} credential presentations were expected but {presentedCount} were received.");
}
// Don't allow balance to go negative. In case this goes below zero
// then there is a problem somewhere because this should not be possible.
if (Balance + registrationRequest.DeltaAmount < Money.Zero)
{
throw new WabiSabiException(WabiSabiErrorCode.NegativeBalance);
}
// Check that the range proofs are of the appropriate bitwidth
var rangeProofWidth = registrationRequest.IsNullRequest ? 0 : Constants.RangeProofWidth;
var allRangeProofsAreCorrectSize = requested.All(x => x.BitCommitments.Count() == rangeProofWidth);
if (!allRangeProofsAreCorrectSize)
{
throw new WabiSabiException(WabiSabiErrorCode.InvalidBitCommitment);
}
// Check all the serial numbers are unique. Note that this is checked separately from
// ensuring that they haven't been used before, because even presenting a previously
// unused credential more than once in the same request is still a double spend.
if (registrationRequest.AreThereDuplicatedSerialNumbers)
{
throw new WabiSabiException(WabiSabiErrorCode.SerialNumberDuplicated);
}
var statements = new List <Statement>();
foreach (var presentation in presented)
{
// Calculate Z using coordinator secret.
var Z = presentation.ComputeZ(CoordinatorSecretKey);
// Add the credential presentation to the statements to be verified.
statements.Add(ProofSystem.ShowCredentialStmt(presentation, Z, CoordinatorParameters));
// Check if the serial numbers have been used before. Note that
// the serial numbers have not yet been verified at this point, but a
// request with an invalid proof and a used serial number should also be
// rejected.
if (SerialNumbers.Contains(presentation.S))
{
throw new WabiSabiException(WabiSabiErrorCode.SerialNumberAlreadyUsed, $"Serial number reused {presentation.S}");
}
}
foreach (var credentialRequest in requested)
{
statements.Add(registrationRequest.IsNullRequest
? ProofSystem.ZeroProofStmt(credentialRequest.Ma)
: ProofSystem.RangeProofStmt(credentialRequest.Ma, credentialRequest.BitCommitments));
}
// Balance proof
if (!registrationRequest.IsNullRequest)
{
var sumCa = presented.Select(x => x.Ca).Sum();
var sumMa = requested.Select(x => x.Ma).Sum();
// A positive Delta_a means the requested credential amounts are larger
// than the presented ones (i.e. input registration, and a negative
// balance correspond to output registration). The equation requires a
// commitment to 0, so the sum of the presented attributes and the
// negated requested attributes are tweaked by delta_a.
var absAmountDelta = new Scalar(registrationRequest.DeltaAmount.Abs());
var deltaA = registrationRequest.DeltaAmount < Money.Zero ? absAmountDelta.Negate() : absAmountDelta;
var balanceTweak = deltaA * Generators.Gg;
statements.Add(ProofSystem.BalanceProofStmt(balanceTweak + sumCa - sumMa));
}
var transcript = BuildTransnscript(registrationRequest.IsNullRequest);
// Verify all statements.
var areProofsValid = ProofSystem.Verify(transcript, statements, registrationRequest.Proofs);
if (!areProofsValid)
{
throw new WabiSabiException(WabiSabiErrorCode.CoordinatorReceivedInvalidProofs);
}
// Issue credentials.
var credentials = requested.Select(x => IssueCredential(x.Ma, RandomNumberGenerator.GetScalar())).ToArray();
// Construct response.
var proofs = ProofSystem.Prove(transcript, credentials.Select(x => x.Knowledge), RandomNumberGenerator);
var macs = credentials.Select(x => x.Mac);
var response = new RegistrationResponseMessage(macs, proofs);
// Register the serial numbers to prevent credential reuse.
foreach (var presentation in presented)
{
SerialNumbers.Add(presentation.S);
}
Balance += registrationRequest.DeltaAmount;
return(response);
}