/// <summary>
/// Validates a certificate by walking the certificate chain for all trust anchor chain, validating the leaf certificate against the chain.
/// </summary>
/// <remarks>Currently, all intermediate certificates must be stored in the system.</remarks>
/// <param name="certificate">The leaf <see cref="X509Certificate2"/> to validate</param>
/// <param name="anchors">The collection of certificates representing anchors or roots of trust.</param>
/// <returns><c>true</c> if at least one anchor has a valid chain of certs that verify trust in the leaf certificate,
/// <c>false</c> if no anchors validate trust in the leaf cert.</returns>
public bool IsTrustedCertificate(X509Certificate2 certificate, X509Certificate2Collection anchors)
{
if (certificate == null)
{
throw new ArgumentNullException("certificate");
}
// if there are no anchors we should always fail
if (CollectionExtensions.IsNullOrEmpty(anchors))
{
this.NotifyUntrusted(certificate);
return false;
}
X509Chain chainBuilder = new X509Chain();
chainBuilder.ChainPolicy = m_policy.Clone();
chainBuilder.ChainPolicy.ExtraStore.Add(anchors);
if (this.HasCertificateResolver)
{
this.ResolveIntermediateIssuers(certificate, chainBuilder.ChainPolicy.ExtraStore);
}
try
{
// We're using the system class as a helper to merely build the chain
// However, we will review each item in the chain ourselves, because we have our own rules...
chainBuilder.Build(certificate);
X509ChainElementCollection chainElements = chainBuilder.ChainElements;
// If we don't have a trust chain, then we obviously have a problem...
if (chainElements.IsNullOrEmpty())
{
this.NotifyUntrusted(certificate);
return false;
}
// walk the chain starting at the leaf and see if we hit any issues before the anchor
foreach (X509ChainElement chainElement in chainElements)
{
if (this.ChainElementHasProblems(chainElement))
{
this.NotifyProblem(chainElement);
// Whoops... problem with at least one cert in the chain. Stop immediately
return false;
}
bool isAnchor = (anchors.FindByThumbprint(chainElement.Certificate.Thumbprint) != null);
if (isAnchor)
{
// Found a valid anchor!
// Because we found an anchor we trust, we can now trust the entire trust chain
return true;
}
}
}
catch(Exception ex)
{
this.NotifyError(certificate, ex);
// just eat it and drop out to return false
}
this.NotifyUntrusted(certificate);
return (false);
}
private void VerifyValidCert(X509Certificate2Collection source, X509Certificate2Collection cached)
{
Assert.NotNull(source);
Assert.NotNull(cached);
Assert.True(cached.Count > 0);
Assert.Equal(source.Count, cached.Count);
source.Enumerate().All((x) => cached.FindByThumbprint(x.Thumbprint) != null);
cached.Enumerate().All((x) => source.FindByThumbprint(x.Thumbprint) != null);
}
