MessageSignature FindTrustedSignature(IncomingMessage message, X509Certificate2Collection anchors)
{
DirectAddress sender = message.Sender;
MessageSignatureCollection signatures = message.SenderSignatures;
MessageSignature lastTrustedSignature = null;
foreach (MessageSignature signature in signatures)
{
if (m_certChainValidator.IsTrustedCertificate(signature.Certificate, anchors) && signature.CheckSignature())
{
if (!sender.HasCertificates)
{
// Can't really check thumbprints etc. So, this is about as good as its going to get
return(signature);
}
if (signature.CheckThumbprint(sender))
{
return(signature);
}
//
// We'll save this guy, but keep looking for a signer whose thumbprint we can verify
// If we can't find one, we'll use the last trusted signer we found.. and just mark the recipient's trust
// enforcement status as Success_ThumbprintMismatch
//
lastTrustedSignature = signature;
}
}
return(lastTrustedSignature);
}
/// <summary>
/// Enforces the trust model on an incoming message by marking
/// the <c>Status</c> property of <see cref="DirectAddress"/> instances for the receivers
/// </summary>
/// <param name="message">The <see cref="IncomingMessage"/> to validate trust for.</param>
/// <exception cref="AgentException">If this message has no signatures</exception>
public void Enforce(IncomingMessage message)
{
if (message == null)
{
throw new ArgumentNullException("message");
}
if (!message.HasSignatures)
{
throw new AgentException(AgentError.UnsignedMessage);
}
//
// The message could have multiple signatures, including, possibly, some not by the sender
//
this.FindSenderSignatures(message);
if (!message.HasSenderSignatures)
{
throw new AgentException(AgentError.MissingSenderSignature);
}
//
// For each recipient, find at least one valid sender signature that the recipient trusts
//
DirectAddress sender = message.Sender;
DirectAddressCollection recipients = message.DomainRecipients;
foreach (DirectAddress recipient in recipients)
{
recipient.Status = TrustEnforcementStatus.Failed;
//
// First, find a signature that this recipient trusts
//
MessageSignature trustedSignature = this.FindTrustedSignature(message, recipient, recipient.TrustAnchors);
if (trustedSignature != null)
{
recipient.Status = TrustEnforcementStatus.Success;
//
// Signature has already been verified by FindTrustedSignature!
//
}
}
}