license switch agpl -> busl1, sprints work, new product advisories

src/AirGap/StellaOps.AirGap.Time/Services/Rfc3161Verifier.cs

@@ -19,7 +19,11 @@ public sealed class Rfc3161Verifier : ITimeTokenVerifier
 
     public TimeTokenFormat Format => TimeTokenFormat.Rfc3161;
 
-    public TimeAnchorValidationResult Verify(ReadOnlySpan<byte> tokenBytes, IReadOnlyList<TimeTrustRoot> trustRoots, out TimeAnchor anchor)
+    public TimeAnchorValidationResult Verify(
+        ReadOnlySpan<byte> tokenBytes,
+        IReadOnlyList<TimeTrustRoot> trustRoots,
+        out TimeAnchor anchor,
+        TimeTokenVerificationOptions? options = null)
     {
         anchor = TimeAnchor.Unknown;
 
@@ -66,13 +70,6 @@ public sealed class Rfc3161Verifier : ITimeTokenVerifier
                 return TimeAnchorValidationResult.Failure("rfc3161-no-signer-certificate");
             }
 
-            // Validate signer certificate against trust roots
-            var validRoot = ValidateAgainstTrustRoots(signerCert, trustRoots);
-            if (validRoot is null)
-            {
-                return TimeAnchorValidationResult.Failure("rfc3161-certificate-not-trusted");
-            }
-
             // Extract signing time from the TSTInfo or signed attributes
             var signingTime = ExtractSigningTime(signedCms, signerInfo);
             if (signingTime is null)
@@ -80,6 +77,27 @@ public sealed class Rfc3161Verifier : ITimeTokenVerifier
                 return TimeAnchorValidationResult.Failure("rfc3161-no-signing-time");
             }
 
+            // Validate signer certificate against trust roots
+            var extraCertificates = BuildExtraCertificates(signedCms, options);
+            var verificationTime = options?.VerificationTime ?? signingTime.Value;
+            var validRoot = ValidateAgainstTrustRoots(
+                signerCert,
+                trustRoots,
+                extraCertificates,
+                verificationTime);
+            if (validRoot is null)
+            {
+                return TimeAnchorValidationResult.Failure("rfc3161-certificate-not-trusted");
+            }
+
+            if (options?.Offline == true)
+            {
+                if (!TryVerifyOfflineRevocation(options, out var revocationReason))
+                {
+                    return TimeAnchorValidationResult.Failure(revocationReason);
+                }
+            }
+
             // Compute certificate fingerprint
             var certFingerprint = Convert.ToHexString(SHA256.HashData(signerCert.RawData)).ToLowerInvariant()[..16];
 
@@ -102,7 +120,11 @@ public sealed class Rfc3161Verifier : ITimeTokenVerifier
         }
     }
 
-    private static TimeTrustRoot? ValidateAgainstTrustRoots(X509Certificate2 signerCert, IReadOnlyList<TimeTrustRoot> trustRoots)
+    private static TimeTrustRoot? ValidateAgainstTrustRoots(
+        X509Certificate2 signerCert,
+        IReadOnlyList<TimeTrustRoot> trustRoots,
+        IReadOnlyList<X509Certificate2> extraCertificates,
+        DateTimeOffset verificationTime)
     {
         foreach (var root in trustRoots)
         {
@@ -122,6 +144,15 @@ public sealed class Rfc3161Verifier : ITimeTokenVerifier
                 chain.ChainPolicy.CustomTrustStore.Add(rootCert);
                 chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck; // Offline mode
                 chain.ChainPolicy.VerificationFlags = X509VerificationFlags.AllowUnknownCertificateAuthority;
+                chain.ChainPolicy.VerificationTime = verificationTime.UtcDateTime;
+
+                foreach (var cert in extraCertificates)
+                {
+                    if (!string.Equals(cert.Thumbprint, rootCert.Thumbprint, StringComparison.OrdinalIgnoreCase))
+                    {
+                        chain.ChainPolicy.ExtraStore.Add(cert);
+                    }
+                }
 
                 if (chain.Build(signerCert))
                 {
@@ -138,6 +169,86 @@ public sealed class Rfc3161Verifier : ITimeTokenVerifier
         return null;
     }
 
+    private static IReadOnlyList<X509Certificate2> BuildExtraCertificates(
+        SignedCms signedCms,
+        TimeTokenVerificationOptions? options)
+    {
+        var extra = new List<X509Certificate2>();
+        if (options?.CertificateChain is { Count: > 0 })
+        {
+            extra.AddRange(options.CertificateChain);
+        }
+
+        foreach (var cert in signedCms.Certificates.Cast<X509Certificate2>())
+        {
+            if (!extra.Any(existing =>
+                    existing.Thumbprint.Equals(cert.Thumbprint, StringComparison.OrdinalIgnoreCase)))
+            {
+                extra.Add(cert);
+            }
+        }
+
+        return extra;
+    }
+
+    private static bool TryVerifyOfflineRevocation(
+        TimeTokenVerificationOptions options,
+        out string reason)
+    {
+        var hasOcsp = options.OcspResponses.Count > 0;
+        var hasCrl = options.Crls.Count > 0;
+
+        if (!hasOcsp && !hasCrl)
+        {
+            reason = "rfc3161-revocation-missing";
+            return false;
+        }
+
+        if (hasOcsp && options.OcspResponses.Any(IsOcspSuccess))
+        {
+            reason = "rfc3161-revocation-ocsp";
+            return true;
+        }
+
+        if (hasCrl && options.Crls.Any(IsCrlParseable))
+        {
+            reason = "rfc3161-revocation-crl";
+            return true;
+        }
+
+        reason = "rfc3161-revocation-invalid";
+        return false;
+    }
+
+    private static bool IsOcspSuccess(byte[] response)
+    {
+        try
+        {
+            var reader = new AsnReader(response, AsnEncodingRules.DER);
+            var sequence = reader.ReadSequence();
+            var status = sequence.ReadEnumeratedValue<OcspResponseStatus>();
+            return status == OcspResponseStatus.Successful;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
+    private static bool IsCrlParseable(byte[] crl)
+    {
+        try
+        {
+            var reader = new AsnReader(crl, AsnEncodingRules.DER);
+            reader.ReadSequence();
+            return true;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
     private static DateTimeOffset? ExtractSigningTime(SignedCms signedCms, SignerInfo signerInfo)
     {
         // Try to get signing time from signed attributes
@@ -215,4 +326,14 @@ public sealed class Rfc3161Verifier : ITimeTokenVerifier
             return null;
         }
     }
+
+    private enum OcspResponseStatus
+    {
+        Successful = 0,
+        MalformedRequest = 1,
+        InternalError = 2,
+        TryLater = 3,
+        SigRequired = 5,
+        Unauthorized = 6
+    }
 }