Add managed TLS interoperability and persisted credentials

2026-09-15 18:04:20 +02:00
parent b76181d9fb
commit 2df79cdd4c
17 changed files with 962 additions and 9 deletions
@@ -0,0 +1,22 @@
+namespace VoiceCat.Crypto;
+
+internal static class PrivateFiles
+{
+    public static void Write(string path, ReadOnlySpan<byte> data)
+    {
+        string destination = Path.GetFullPath(path);
+        string temporary = destination + "." + Guid.NewGuid().ToString("N") + ".tmp";
+        try
+        {
+            var options = new FileStreamOptions { Mode = FileMode.CreateNew, Access = FileAccess.Write, Share = FileShare.None };
+            if (!OperatingSystem.IsWindows()) options.UnixCreateMode = UnixFileMode.UserRead | UnixFileMode.UserWrite;
+            using (var stream = new FileStream(temporary, options))
+            {
+                stream.Write(data);
+                stream.Flush(flushToDisk: true);
+            }
+            File.Move(temporary, destination, overwrite: true);
+        }
+        finally { if (File.Exists(temporary)) File.Delete(temporary); }
+    }
+}
@@ -0,0 +1,75 @@
+using System.Security.Cryptography;
+using System.Security.Cryptography.X509Certificates;
+using System.Text;
+
+namespace VoiceCat.Crypto;
+
+public sealed class ServerCredentials : IDisposable
+{
+    private readonly X509Certificate2 certificate;
+    private bool disposed;
+
+    private ServerCredentials(ServerIdentity identity, X509Certificate2 certificate)
+    {
+        Identity = identity;
+        this.certificate = certificate;
+    }
+
+    public ServerIdentity Identity { get; }
+    public string CertificateFingerprint => Convert.ToHexString(SHA256.HashData(certificate.RawData));
+
+    public static ServerCredentials LoadOrCreate(string directory, string serverName)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(serverName);
+        Directory.CreateDirectory(directory);
+        string identityPath = Path.Combine(directory, "identity.key");
+        string certificatePath = Path.Combine(directory, "server.crt");
+        string keyPath = Path.Combine(directory, "server.key");
+        bool hasIdentity = File.Exists(identityPath);
+        bool hasCertificate = File.Exists(certificatePath);
+        bool hasKey = File.Exists(keyPath);
+        if (hasIdentity && hasCertificate && hasKey)
+        {
+            var identity = ServerIdentity.Load(identityPath);
+            try { return new(identity, X509Certificate2.CreateFromPemFile(certificatePath, keyPath)); }
+            catch { identity.Dispose(); throw; }
+        }
+        if (hasIdentity || hasCertificate || hasKey)
+            throw new InvalidDataException("Server credentials are incomplete; restore the missing files before starting.");
+        var generated = ServerIdentity.Generate();
+        try
+        {
+            using var key = ECDsa.Create(ECCurve.NamedCurves.nistP256);
+            var name = new X500DistinguishedNameBuilder();
+            name.AddCommonName(serverName);
+            var request = new CertificateRequest(name.Build(), key, HashAlgorithmName.SHA256);
+            request.CertificateExtensions.Add(new X509KeyUsageExtension(X509KeyUsageFlags.DigitalSignature, true));
+            var san = new SubjectAlternativeNameBuilder();
+            san.AddUri(new Uri("urn:voicecat:identity:ed25519:" + Convert.ToHexString(generated.PublicKey).ToLowerInvariant()));
+            request.CertificateExtensions.Add(san.Build());
+            using var created = request.CreateSelfSigned(DateTimeOffset.UtcNow.AddMinutes(-5), DateTimeOffset.UtcNow.AddYears(10));
+            string certificatePem = created.ExportCertificatePem();
+            string privateKeyPem = key.ExportPkcs8PrivateKeyPem();
+            generated.Save(identityPath);
+            PrivateFiles.Write(certificatePath, Encoding.UTF8.GetBytes(certificatePem));
+            PrivateFiles.Write(keyPath, Encoding.UTF8.GetBytes(privateKeyPem));
+            return new(generated, X509Certificate2.CreateFromPem(certificatePem, privateKeyPem));
+        }
+        catch { generated.Dispose(); throw; }
+    }
+
+    public TlsSession CreateTlsSession()
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        using var key = certificate.GetECDsaPrivateKey() ?? throw new InvalidDataException("Server TLS certificate requires an ECDSA key.");
+        return TlsSession.CreateServer(certificate.ExportCertificatePem(), key.ExportPkcs8PrivateKeyPem());
+    }
+
+    public void Dispose()
+    {
+        if (disposed) return;
+        disposed = true;
+        Identity.Dispose();
+        certificate.Dispose();
+    }
+}
@@ -0,0 +1,58 @@
+using System.Security.Cryptography;
+using Org.BouncyCastle.Crypto.Parameters;
+
+namespace VoiceCat.Crypto;
+
+public sealed class ServerIdentity : IDisposable
+{
+    private readonly byte[] seed;
+    private readonly byte[] publicKey;
+    private bool disposed;
+
+    private ServerIdentity(byte[] seed)
+    {
+        this.seed = seed;
+        publicKey = new Ed25519PrivateKeyParameters(seed, 0).GeneratePublicKey().GetEncoded();
+    }
+
+    public byte[] PublicKey => (byte[])publicKey.Clone();
+    public string Fingerprint => Convert.ToHexString(SHA256.HashData(publicKey));
+
+    public static ServerIdentity Generate() => new(RandomNumberGenerator.GetBytes(32));
+
+    public static ServerIdentity Load(string path)
+    {
+        byte[] data = File.ReadAllBytes(path);
+        try
+        {
+            if (data.Length != 96) throw new InvalidDataException("Server identity must contain 96 bytes.");
+            var identity = new ServerIdentity(data.AsSpan(32, 32).ToArray());
+            if (!CryptographicOperations.FixedTimeEquals(identity.publicKey, data.AsSpan(0, 32)) ||
+                !CryptographicOperations.FixedTimeEquals(identity.publicKey, data.AsSpan(64, 32)))
+            {
+                identity.Dispose();
+                throw new InvalidDataException("Server identity public key does not match its seed.");
+            }
+            return identity;
+        }
+        finally { CryptographicOperations.ZeroMemory(data); }
+    }
+
+    public void Save(string path)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        byte[] data = new byte[96];
+        publicKey.CopyTo(data, 0);
+        seed.CopyTo(data, 32);
+        publicKey.CopyTo(data, 64);
+        try { PrivateFiles.Write(path, data); }
+        finally { CryptographicOperations.ZeroMemory(data); }
+    }
+
+    public void Dispose()
+    {
+        if (disposed) return;
+        disposed = true;
+        CryptographicOperations.ZeroMemory(seed);
+    }
+}
@@ -0,0 +1,208 @@
+using System.Security.Cryptography;
+using Org.BouncyCastle.Crypto;
+using Org.BouncyCastle.OpenSsl;
+using Org.BouncyCastle.Tls;
+using Org.BouncyCastle.Tls.Crypto;
+using Org.BouncyCastle.Tls.Crypto.Impl.BC;
+
+namespace VoiceCat.Crypto;
+
+public sealed class TlsSession : IDisposable
+{
+    private readonly TlsProtocol protocol;
+    private readonly bool isClient;
+    private readonly byte[] scratch = new byte[16384];
+    private byte[]? clientToServerKey;
+    private byte[]? serverToClientKey;
+    private bool disposed;
+
+    private TlsSession(TlsProtocol protocol, bool isClient)
+    {
+        this.protocol = protocol;
+        this.isClient = isClient;
+    }
+
+    public bool IsReady => !disposed && clientToServerKey is not null && serverToClientKey is not null && !protocol.IsClosed;
+    public string? PeerCertificateFingerprint { get; private set; }
+    public int PendingCiphertextBytes => protocol.GetAvailableOutputBytes();
+
+    public void Close()
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        protocol.Close();
+    }
+
+    public void CompleteInput()
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        protocol.CloseInput();
+    }
+
+    public static TlsSession CreateClient(Func<string, bool> acceptCertificate)
+    {
+        ArgumentNullException.ThrowIfNull(acceptCertificate);
+        var protocol = new TlsClientProtocol();
+        var session = new TlsSession(protocol, true);
+        protocol.Connect(new ClientPeer(session, acceptCertificate));
+        return session;
+    }
+
+    public static TlsSession CreateServer(string certificatePem, string privateKeyPem)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(certificatePem);
+        ArgumentException.ThrowIfNullOrWhiteSpace(privateKeyPem);
+        var protocol = new TlsServerProtocol();
+        var session = new TlsSession(protocol, false);
+        protocol.Accept(new ServerPeer(session, certificatePem, privateKeyPem));
+        return session;
+    }
+
+    public void ReceiveCiphertext(ReadOnlySpan<byte> input)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        while (!input.IsEmpty)
+        {
+            int count = Math.Min(input.Length, scratch.Length);
+            input[..count].CopyTo(scratch);
+            protocol.OfferInput(scratch, 0, count);
+            input = input[count..];
+        }
+    }
+
+    public int DrainCiphertext(Span<byte> output)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        int count = protocol.ReadOutput(scratch, 0, Math.Min(output.Length, scratch.Length));
+        scratch.AsSpan(0, count).CopyTo(output);
+        return count;
+    }
+
+    public int ReadPlaintext(Span<byte> output)
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        int count = protocol.ReadInput(scratch, 0, Math.Min(output.Length, scratch.Length));
+        scratch.AsSpan(0, count).CopyTo(output);
+        CryptographicOperations.ZeroMemory(scratch.AsSpan(0, count));
+        return count;
+    }
+
+    public void WritePlaintext(ReadOnlySpan<byte> input)
+    {
+        RequireReady();
+        protocol.WriteApplicationData(input);
+    }
+
+    public MediaEncryptor CreateMediaEncryptor()
+    {
+        byte[] key = ExportMediaKey(isClient ? (byte)0 : (byte)1);
+        try { return new(key); }
+        finally { CryptographicOperations.ZeroMemory(key); }
+    }
+
+    public MediaDecryptor CreateMediaDecryptor()
+    {
+        byte[] key = ExportMediaKey(isClient ? (byte)1 : (byte)0);
+        try { return new(key); }
+        finally { CryptographicOperations.ZeroMemory(key); }
+    }
+
+    internal byte[] ExportMediaKey(byte direction)
+    {
+        RequireReady();
+        ArgumentOutOfRangeException.ThrowIfGreaterThan(direction, (byte)1);
+        return (byte[])(direction == 0 ? clientToServerKey! : serverToClientKey!).Clone();
+    }
+
+    private void CompleteHandshake(TlsContext context)
+    {
+        // BouncyCastle destroys exporter secrets after this callback returns.
+        clientToServerKey = context.ExportKeyingMaterial("voicecat media v1", [0], 32);
+        serverToClientKey = context.ExportKeyingMaterial("voicecat media v1", [1], 32);
+    }
+
+    private void RequireReady()
+    {
+        ObjectDisposedException.ThrowIf(disposed, this);
+        if (!IsReady) throw new InvalidOperationException("TLS handshake has not completed or the session is closed.");
+    }
+
+    public void Dispose()
+    {
+        if (disposed) return;
+        disposed = true;
+        try { protocol.Close(); }
+        finally
+        {
+            if (clientToServerKey is not null) CryptographicOperations.ZeroMemory(clientToServerKey);
+            if (serverToClientKey is not null) CryptographicOperations.ZeroMemory(serverToClientKey);
+            CryptographicOperations.ZeroMemory(scratch);
+        }
+    }
+
+    private sealed class ClientPeer(TlsSession session, Func<string, bool> acceptCertificate)
+        : DefaultTlsClient(new BcTlsCrypto())
+    {
+        protected override ProtocolVersion[] GetSupportedVersions() => [ProtocolVersion.TLSv13];
+        protected override int[] GetSupportedCipherSuites() => CipherSuites;
+        public override TlsAuthentication GetAuthentication() => new Authentication(session, acceptCertificate);
+        public override void NotifyHandshakeComplete()
+        {
+            base.NotifyHandshakeComplete();
+            session.CompleteHandshake(m_context);
+        }
+    }
+
+    private sealed class Authentication(TlsSession session, Func<string, bool> acceptCertificate) : TlsAuthentication
+    {
+        public void NotifyServerCertificate(TlsServerCertificate serverCertificate)
+        {
+            var chain = serverCertificate.Certificate.GetCertificateList();
+            if (chain.Length == 0) throw new TlsFatalAlert(AlertDescription.bad_certificate);
+            string fingerprint = Convert.ToHexString(SHA256.HashData(chain[0].GetEncoded()));
+            session.PeerCertificateFingerprint = fingerprint;
+            if (!acceptCertificate(fingerprint)) throw new TlsFatalAlert(AlertDescription.bad_certificate);
+        }
+
+        public TlsCredentials? GetClientCredentials(Org.BouncyCastle.Tls.CertificateRequest certificateRequest) => null;
+    }
+
+    private sealed class ServerPeer : DefaultTlsServer
+    {
+        private readonly TlsSession session;
+        private readonly byte[] certificateDer;
+        private readonly AsymmetricKeyParameter privateKey;
+
+        public ServerPeer(TlsSession session, string certificatePem, string privateKeyPem) : base(new BcTlsCrypto())
+        {
+            this.session = session;
+            using var certificate = System.Security.Cryptography.X509Certificates.X509Certificate2.CreateFromPem(certificatePem);
+            certificateDer = certificate.RawData;
+            using var reader = new StringReader(privateKeyPem);
+            privateKey = (AsymmetricKeyParameter)new PemReader(reader).ReadObject();
+            if (privateKey is not Org.BouncyCastle.Crypto.Parameters.ECPrivateKeyParameters)
+                throw new ArgumentException("Server TLS credentials require an ECDSA key.", nameof(privateKeyPem));
+        }
+
+        protected override ProtocolVersion[] GetSupportedVersions() => [ProtocolVersion.TLSv13];
+        protected override int[] GetSupportedCipherSuites() => CipherSuites;
+        public override TlsCredentials GetCredentials()
+        {
+            var certificate = new Certificate([], [new CertificateEntry(Crypto.CreateCertificate(certificateDer), null)]);
+            return new BcDefaultTlsCredentialedSigner(new TlsCryptoParameters(m_context), (BcTlsCrypto)Crypto,
+                privateKey, certificate, new SignatureAndHashAlgorithm(Org.BouncyCastle.Tls.HashAlgorithm.sha256, SignatureAlgorithm.ecdsa));
+        }
+
+        public override void NotifyHandshakeComplete()
+        {
+            base.NotifyHandshakeComplete();
+            session.CompleteHandshake(m_context);
+        }
+    }
+
+    private static int[] CipherSuites =>
+    [
+        CipherSuite.TLS_AES_128_GCM_SHA256,
+        CipherSuite.TLS_AES_256_GCM_SHA384,
+        CipherSuite.TLS_CHACHA20_POLY1305_SHA256
+    ];
+}
@@ -0,0 +1,72 @@
+using System.Text;
+
+namespace VoiceCat.Crypto;
+
+public enum TofuStatus { FirstConnect, Matched, Mismatch }
+
+public sealed class TofuStore
+{
+    private readonly string path;
+    private readonly Dictionary<string, string> pins = new(StringComparer.Ordinal);
+
+    public TofuStore(string path)
+    {
+        this.path = Path.GetFullPath(path);
+        if (!File.Exists(this.path)) return;
+        foreach (string line in File.ReadLines(this.path))
+        {
+            if (string.IsNullOrWhiteSpace(line) || line.StartsWith('#')) continue;
+            string[] parts = line.Split((char[]?)null, StringSplitOptions.RemoveEmptyEntries);
+            if (parts.Length != 2) throw new InvalidDataException("Malformed TOFU pin entry.");
+            pins[parts[0]] = NormalizeFingerprint(parts[1]);
+        }
+    }
+
+    public TofuStatus Check(string host, ushort port, string fingerprint)
+    {
+        string key = Endpoint(host, port);
+        string normalized = NormalizeFingerprint(fingerprint);
+        return !pins.TryGetValue(key, out var pin) ? TofuStatus.FirstConnect :
+            pin == normalized ? TofuStatus.Matched : TofuStatus.Mismatch;
+    }
+
+    public void Pin(string host, ushort port, string fingerprint)
+    {
+        string key = Endpoint(host, port);
+        string value = NormalizeFingerprint(fingerprint);
+        var updated = new Dictionary<string, string>(pins, StringComparer.Ordinal) { [key] = value };
+        Save(updated);
+        pins[key] = value;
+    }
+
+    public void Remove(string host, ushort port)
+    {
+        string key = Endpoint(host, port);
+        var updated = new Dictionary<string, string>(pins, StringComparer.Ordinal);
+        updated.Remove(key);
+        Save(updated);
+        pins.Remove(key);
+    }
+
+    private void Save(Dictionary<string, string> updated)
+    {
+        string contents = string.Concat(updated.OrderBy(pair => pair.Key, StringComparer.Ordinal).Select(pair => $"{pair.Key} {pair.Value}\n"));
+        PrivateFiles.Write(path, Encoding.UTF8.GetBytes(contents));
+    }
+
+    private static string Endpoint(string host, ushort port)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(host);
+        if (host.Any(char.IsWhiteSpace)) throw new ArgumentException("Host cannot contain whitespace.", nameof(host));
+        ArgumentOutOfRangeException.ThrowIfZero(port);
+        return $"{host}:{port}";
+    }
+
+    private static string NormalizeFingerprint(string fingerprint)
+    {
+        ArgumentNullException.ThrowIfNull(fingerprint);
+        if (fingerprint.Length != 64 || !fingerprint.All(Uri.IsHexDigit))
+            throw new InvalidDataException("TLS certificate fingerprints must contain 64 hexadecimal characters.");
+        return fingerprint.ToLowerInvariant();
+    }
+}