AES

Libraries/Esiur/Net/Packets/EpAuthPacket.cs

@@ -158,7 +158,8 @@ public class EpAuthPacket : Packet
         if (Command == EpAuthPacketCommand.Initialize)
         {
             AuthMode = (AuthenticationMode)(data[offset] >> 2 & 0x3);
-            EncryptionMode = (EncryptionMode)(data[offset++] & 0x7);
+            // Authentication occupies bits 2-3; encryption is confined to bits 0-1.
+            EncryptionMode = (EncryptionMode)(data[offset++] & 0x3);
         }
         else if (Command == EpAuthPacketCommand.Acknowledge)
         {

Libraries/Esiur/Net/Packets/EpAuthPacketHeader.cs

@@ -22,6 +22,7 @@ namespace Esiur.Net.Packets
         Identity,
         AuthenticationProtocol,
         AuthenticationData,
-        ErrorMessage
+        ErrorMessage,
+        CipherNonce
     }
 }

Libraries/Esiur/Net/Sockets/FrameworkWebSocket.cs

@@ -28,6 +28,8 @@ namespace Esiur.Net.Sockets
         ArraySegment<byte> websocketReceiveBufferSegment;
 
         object sendLock = new object();
+        readonly SemaphoreSlim sendSemaphore = new SemaphoreSlim(1, 1);
+        int sendFailureNotified;
         bool held;
 
         public event DestroyedEvent OnDestroy;
@@ -70,7 +72,7 @@ namespace Esiur.Net.Sockets
 
         public void Send(byte[] message)
         {
-
+            byte[] queued = null;
             lock (sendLock)
             {
                 if (held)
@@ -79,16 +81,18 @@ namespace Esiur.Net.Sockets
                 }
                 else
                 {
-                    totalSent += message.Length;
+                    queued = (byte[])message.Clone();
-                    sock.SendAsync(new ArraySegment<byte>(message), WebSocketMessageType.Binary,
-                        true, new System.Threading.CancellationToken());
                 }
             }
+
+            if (queued != null)
+                ObserveSend(QueueSend(queued));
         }
 
 
         public void Send(byte[] message, int offset, int size)
         {
+            byte[] queued = null;
             lock (sendLock)
             {
                 if (held)
@@ -97,12 +101,13 @@ namespace Esiur.Net.Sockets
                 }
                 else
                 {
-                    totalSent += size;
+                    queued = new byte[size];
-
+                    Buffer.BlockCopy(message, offset, queued, 0, size);
-                    sock.SendAsync(new ArraySegment<byte>(message, offset, size),
-                        WebSocketMessageType.Binary, true, new System.Threading.CancellationToken());
                 }
             }
+
+            if (queued != null)
+                ObserveSend(QueueSend(queued));
         }
 
 
@@ -184,41 +189,85 @@ namespace Esiur.Net.Sockets
 
         public void Unhold()
         {
+            byte[] message;
             lock (sendLock)
             {
                 held = false;
-
+                message = sendNetworkBuffer.Read();
-                var message = sendNetworkBuffer.Read();
-
-                if (message == null)
-                    return;
-
-                totalSent += message.Length;
-
-                sock.SendAsync(new ArraySegment<byte>(message), WebSocketMessageType.Binary,
-                    true, new System.Threading.CancellationToken());
-
             }
+
+            if (message != null)
+                ObserveSend(QueueSend(message));
         }
 
         public async AsyncReply<bool> SendAsync(byte[] message, int offset, int length)
         {
-            if (held)
+            byte[] queued = null;
+            lock (sendLock)
             {
-                sendNetworkBuffer.Write(message, (uint)offset, (uint)length);
+                if (held)
-            }
+                {
-            else
+                    sendNetworkBuffer.Write(message, (uint)offset, (uint)length);
-            {
+                }
-                totalSent += length;
+                else
-
+                {
-                await sock.SendAsync(new ArraySegment<byte>(message, offset, length),
+                    queued = new byte[length];
-                    WebSocketMessageType.Binary, true, new System.Threading.CancellationToken());
+                    Buffer.BlockCopy(message, offset, queued, 0, length);
+                }
             }
 
+            if (queued != null)
+                await QueueSend(queued);
 
             return true;
         }
 
+        async Task QueueSend(byte[] message)
+        {
+            await sendSemaphore.WaitAsync();
+            try
+            {
+                var socket = sock ?? throw new InvalidOperationException("WebSocket is closed.");
+                await socket.SendAsync(
+                    new ArraySegment<byte>(message),
+                    WebSocketMessageType.Binary,
+                    true,
+                    CancellationToken.None);
+                Interlocked.Add(ref totalSent, message.Length);
+            }
+            catch
+            {
+                NotifySendFailure();
+                throw;
+            }
+            finally
+            {
+                sendSemaphore.Release();
+            }
+        }
+
+        void ObserveSend(Task task)
+        {
+            _ = task.ContinueWith(
+                completed =>
+                {
+                    // Observe the exception; QueueSend already closed/notified the receiver.
+                    _ = completed.Exception;
+                },
+                CancellationToken.None,
+                TaskContinuationOptions.OnlyOnFaulted,
+                TaskScheduler.Default);
+        }
+
+        void NotifySendFailure()
+        {
+            if (Interlocked.Exchange(ref sendFailureNotified, 1) == 0)
+            {
+                try { sock?.Abort(); } catch { }
+                Receiver?.NetworkClose(this);
+            }
+        }
+
         public ISocket Accept()
         {
             throw new NotImplementedException();

Libraries/Esiur/Protocol/EpConnectionContext.cs

@@ -3,6 +3,7 @@ using Esiur.Data;
 using Esiur.Net.Packets;
 using Esiur.Resource;
 using Esiur.Security.Authority;
+using Esiur.Security.Cryptography;
 using Esiur.Security.Membership;
 using Esiur.Security.Permissions;
 using System;
@@ -40,6 +41,16 @@ public class EpConnectionContext : IResourceContext
     public string Identity { get; set; }
     public string AuthenticationProtocol { get; set; } = "hash";
 
+    /// <summary>
+    /// Controls whether the authenticated session key must protect EP traffic.
+    /// </summary>
+    public EncryptionMode EncryptionMode { get; set; } = EncryptionMode.None;
+
+    /// <summary>
+    /// Encryption provider protocol names offered to the responder, in preference order.
+    /// </summary>
+    public string[] EncryptionProviders { get; set; } = new[] { "aes-gcm" };
+
     public bool AutoReconnect { get; set; } = false;
 
     public uint ReconnectInterval { get; set; } = 5;

Libraries/Esiur/Protocol/EpServer.cs

@@ -59,6 +59,17 @@ public class EpServer : NetworkServer<EpConnection>, IResource
     //[Attribute]
     public string[] AllowedAuthenticationProviders { get; set; }
 
+    /// <summary>
+    /// Encryption provider protocol names that incoming connections may negotiate.
+    /// Providers must also be registered with the server Warehouse.
+    /// </summary>
+    public string[] AllowedEncryptionProviders { get; set; } = Array.Empty<string>();
+
+    /// <summary>
+    /// Rejects incoming sessions that do not request authenticated encryption.
+    /// </summary>
+    public bool RequireEncryption { get; set; }
+
     //[Attribute]
     public bool AllowUnauthorizedAccess { get; set; }
 

Libraries/Esiur/Resource/Attributes/AuditingManagerAttribute.cs

@@ -0,0 +1,13 @@
+using Esiur.Security.Management;
+using System;
+
+namespace Esiur.Resource;
+
+/// <summary>
+/// Associates a registered auditing-manager implementation with a resource type.
+/// </summary>
+[AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
+public sealed class AuditingManagerAttribute<T> : Attribute
+    where T : IAuditingManager
+{
+}

Libraries/Esiur/Resource/Attributes/PermissionsManagerAttribute.cs

@@ -0,0 +1,13 @@
+using Esiur.Security.Permissions;
+using System;
+
+namespace Esiur.Resource;
+
+/// <summary>
+/// Associates a registered permissions-manager implementation with a resource type.
+/// </summary>
+[AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
+public sealed class PermissionsManagerAttribute<T> : Attribute
+    where T : IPermissionsManager
+{
+}

Libraries/Esiur/Resource/Attributes/RateControlManagerAttribute.cs

@@ -0,0 +1,13 @@
+using Esiur.Security.Management;
+using System;
+
+namespace Esiur.Resource;
+
+/// <summary>
+/// Associates a registered rate-control-manager implementation with a resource type.
+/// </summary>
+[AttributeUsage(AttributeTargets.Class, AllowMultiple = true, Inherited = true)]
+public sealed class RateControlManagerAttribute<T> : Attribute
+    where T : IRateControlManager
+{
+}

Libraries/Esiur/Resource/Warehouse.cs

@@ -30,6 +30,7 @@ using Esiur.Net.Packets;
 using Esiur.Protocol;
 using Esiur.Proxy;
 using Esiur.Security.Authority;
+using Esiur.Security.Cryptography;
 using Esiur.Security.Permissions;
 using Esiur.Security.RateLimiting;
 using Org.BouncyCastle.Asn1.Cms;
@@ -88,6 +89,8 @@ public class Warehouse
 
 
     Map<string, IAuthenticationProvider> _authenticationProviders = new Map<string, IAuthenticationProvider>();
+    readonly ConcurrentDictionary<string, IEncryptionProvider> _encryptionProviders
+        = new ConcurrentDictionary<string, IEncryptionProvider>(StringComparer.Ordinal);
     List<IPermissionsManager> _permissionsManagers = new List<IPermissionsManager>();
     readonly ConcurrentDictionary<string, RatePolicy> _ratePolicies
         = new ConcurrentDictionary<string, RatePolicy>(StringComparer.Ordinal);
@@ -123,6 +126,30 @@ public class Warehouse
         _authenticationProviders.Add(name, provider);
     }
 
+    /// <summary>
+    /// Registers an encryption provider using its default protocol name.
+    /// </summary>
+    public void RegisterEncryptionProvider(IEncryptionProvider provider)
+    {
+        if (provider == null)
+            throw new ArgumentNullException(nameof(provider));
+
+        RegisterEncryptionProvider(provider.DefaultName, provider);
+    }
+
+    /// <summary>
+    /// Registers an encryption provider under a protocol name used during session negotiation.
+    /// </summary>
+    public void RegisterEncryptionProvider(string name, IEncryptionProvider provider)
+    {
+        if (string.IsNullOrWhiteSpace(name))
+            throw new ArgumentException("An encryption provider name is required.", nameof(name));
+        if (provider == null)
+            throw new ArgumentNullException(nameof(provider));
+        if (!_encryptionProviders.TryAdd(name, provider))
+            throw new InvalidOperationException($"An encryption provider named `{name}` is already registered.");
+    }
+
 
     public void RegisterPermissionsManager(IPermissionsManager manager)
     {
@@ -179,6 +206,32 @@ public class Warehouse
         return null;
     }
 
+    /// <summary>
+    /// Gets a registered encryption provider or throws when the protocol is unavailable.
+    /// </summary>
+    public IEncryptionProvider GetEncryptionProvider(string name)
+    {
+        if (TryGetEncryptionProvider(name) is { } provider)
+            return provider;
+
+        throw new InvalidOperationException($"Encryption provider `{name}` was not found.");
+    }
+
+    /// <summary>
+    /// Attempts to get a registered encryption provider by protocol name.
+    /// </summary>
+    public IEncryptionProvider? TryGetEncryptionProvider(string name)
+        => !string.IsNullOrWhiteSpace(name)
+            && _encryptionProviders.TryGetValue(name, out var provider)
+                ? provider
+                : null;
+
+    /// <summary>
+    /// Returns a snapshot of encryption protocol names registered in this Warehouse.
+    /// </summary>
+    public string[] GetEncryptionProviderNames()
+        => _encryptionProviders.Keys.OrderBy(x => x, StringComparer.Ordinal).ToArray();
+
 
     public Warehouse() : this(new WarehouseConfiguration())
     {

Libraries/Esiur/Resource/WarehouseConfiguration.cs

@@ -11,6 +11,16 @@ public sealed class WarehouseConfiguration
     public ParserConfiguration Parser { get; set; } = new ParserConfiguration();
     public ResourceAttachmentConfiguration ResourceAttachments { get; set; } = new ResourceAttachmentConfiguration();
     public ConnectionConfiguration Connections { get; set; } = new ConnectionConfiguration();
+    public EncryptionConfiguration Encryption { get; set; } = new EncryptionConfiguration();
+}
+
+/// <summary>
+/// Bounds encrypted transport records before any peer-controlled allocation occurs.
+/// A value of zero disables the limit.
+/// </summary>
+public sealed class EncryptionConfiguration
+{
+    public uint MaximumRecordSize { get; set; } = 8 * 1024 * 1024 + 1024;
 }
 
 /// <summary>

Libraries/Esiur/Security/Authority/Session.cs

@@ -55,7 +55,7 @@ public sealed class SessionHeaders : IndexedStructure
     public object? SupportedHashAlgorithms { get; set; }
 
     [Index((int)EpAuthPacketHeader.SupportedCiphers)]
-    public object? SupportedCiphers { get; set; }
+    public string[]? SupportedCiphers { get; set; }
 
     [Index((int)EpAuthPacketHeader.SupportedCompression)]
     public object? SupportedCompression { get; set; }
@@ -64,7 +64,7 @@ public sealed class SessionHeaders : IndexedStructure
     public object? SupportedMultiFactorAuthentications { get; set; }
 
     [Index((int)EpAuthPacketHeader.CipherType)]
-    public object? CipherType { get; set; }
+    public string? CipherType { get; set; }
 
     [Index((int)EpAuthPacketHeader.CipherKey)]
     public byte[]? CipherKey { get; set; }
@@ -93,6 +93,13 @@ public sealed class SessionHeaders : IndexedStructure
     [Index((int)EpAuthPacketHeader.ErrorMessage)]
     public string? ErrorMessage { get; set; }
 
+    /// <summary>
+    /// Fresh public nonce used with the authenticated session key to derive unique
+    /// per-connection encryption keys. This value is not a secret key.
+    /// </summary>
+    [Index((int)EpAuthPacketHeader.CipherNonce)]
+    public byte[]? CipherNonce { get; set; }
+
     internal SessionHeaders Copy() => (SessionHeaders)MemberwiseClone();
 }
 
@@ -107,6 +114,8 @@ public class Session
 
     //public IKeyExchanger KeyExchanger { get; set; } = null;
     public ISymetricCipher SymetricCipher { get; set; } = null;
+    public IEncryptionProvider EncryptionProvider { get; set; } = null;
+    public bool EncryptionActive { get; internal set; }
 
 
     public SessionHeaders LocalHeaders { get; set; } = new SessionHeaders();

Libraries/Esiur/Security/Cryptography/AesEncryptionProvider.cs

@@ -0,0 +1,482 @@
+using Esiur.Security.Authority;
+using Org.BouncyCastle.Crypto;
+using Org.BouncyCastle.Crypto.Digests;
+using Org.BouncyCastle.Crypto.Generators;
+using Org.BouncyCastle.Crypto.Modes;
+using Org.BouncyCastle.Crypto.Parameters;
+using System;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace Esiur.Security.Cryptography;
+
+/// <summary>
+/// Creates AES-256-GCM record ciphers. Session keys and nonce prefixes are
+/// derived with HKDF-SHA256 and separated by protocol direction and purpose.
+/// </summary>
+public sealed class AesEncryptionProvider : IEncryptionProvider
+{
+    public const string Name = "aes-gcm";
+
+    public string DefaultName => Name;
+
+    public uint MaximumRecordOverhead => 8 + 16;
+
+    public ISymetricCipher CreateCipher(EncryptionContext context)
+        => new AesGcmSymetricCipher(context);
+}
+
+/// <summary>
+/// AES-256-GCM session record cipher.
+///
+/// A record contains an eight-byte, big-endian sequence followed by ciphertext
+/// and a sixteen-byte GCM tag. The transport's four-byte record length and the
+/// sequence are authenticated as associated data. Sequence numbers are implicit
+/// state as well as explicit record fields, so replay and reordering fail closed.
+/// </summary>
+public sealed class AesGcmSymetricCipher : ISymetricCipher, IDisposable
+{
+    const int KeySize = 32;
+    const int NoncePrefixSize = 4;
+    const int SequenceSize = 8;
+    const int TagSize = 16;
+    const int RecordOverhead = SequenceSize + TagSize;
+    const int AadSize = 4 + SequenceSize;
+    const int MinimumSharedKeySize = 16;
+    const int MaximumSharedKeySize = 1024;
+    const int MinimumPeerNonceSize = 16;
+    const int MaximumPeerNonceSize = 64;
+
+    static readonly byte[] ContextLabel = Encoding.ASCII.GetBytes("esiur/ep/aes-256-gcm/context/v3");
+    static readonly byte[] InitiatorToResponderKeyLabel = Encoding.ASCII.GetBytes("esiur/ep/aes-256-gcm/v1/initiator-to-responder/key");
+    static readonly byte[] ResponderToInitiatorKeyLabel = Encoding.ASCII.GetBytes("esiur/ep/aes-256-gcm/v1/responder-to-initiator/key");
+    static readonly byte[] InitiatorToResponderNonceLabel = Encoding.ASCII.GetBytes("esiur/ep/aes-256-gcm/v1/initiator-to-responder/nonce");
+    static readonly byte[] ResponderToInitiatorNonceLabel = Encoding.ASCII.GetBytes("esiur/ep/aes-256-gcm/v1/responder-to-initiator/nonce");
+
+    readonly object _sendLock = new object();
+    readonly object _receiveLock = new object();
+    readonly byte[] _contextSalt;
+    readonly byte[] _sendKeyLabel;
+    readonly byte[] _receiveKeyLabel;
+    readonly byte[] _sendNonceLabel;
+    readonly byte[] _receiveNonceLabel;
+
+    byte[] _sendKey;
+    byte[] _receiveKey;
+    byte[] _sendNoncePrefix;
+    byte[] _receiveNoncePrefix;
+    ulong _sendSequence;
+    ulong _receiveSequence;
+    bool _keyInitialized;
+    bool _disposed;
+
+    internal AesGcmSymetricCipher(EncryptionContext context)
+    {
+        if (context == null)
+            throw new ArgumentNullException(nameof(context));
+
+        ValidateContext(context);
+
+        _contextSalt = ComposeContextSalt(context);
+
+        if (context.Direction == AuthenticationDirection.Initiator)
+        {
+            _sendKeyLabel = InitiatorToResponderKeyLabel;
+            _receiveKeyLabel = ResponderToInitiatorKeyLabel;
+            _sendNonceLabel = InitiatorToResponderNonceLabel;
+            _receiveNonceLabel = ResponderToInitiatorNonceLabel;
+        }
+        else
+        {
+            _sendKeyLabel = ResponderToInitiatorKeyLabel;
+            _receiveKeyLabel = InitiatorToResponderKeyLabel;
+            _sendNonceLabel = ResponderToInitiatorNonceLabel;
+            _receiveNonceLabel = InitiatorToResponderNonceLabel;
+        }
+
+        var acceptedKey = SetKey(context.Key);
+        Clear(acceptedKey);
+    }
+
+    /// <summary>Identifier retained for compatibility with <see cref="ISymetricCipher"/>.</summary>
+    public ushort Identifier => (ushort)SymetricEncryptionAlgorithmType.AES;
+
+    public byte[] Encrypt(byte[] data)
+    {
+        if (data == null)
+            throw new ArgumentNullException(nameof(data));
+
+        if (data.Length > int.MaxValue - RecordOverhead)
+            throw new ArgumentOutOfRangeException(nameof(data), "The encrypted record exceeds the 32-bit record length.");
+
+        lock (_sendLock)
+        {
+            ThrowIfDisposed();
+
+            if (_sendSequence == ulong.MaxValue)
+                throw new CryptographicException("The AES-GCM send sequence is exhausted.");
+
+            var sequence = _sendSequence;
+            var recordLength = data.Length + RecordOverhead;
+            var nonce = ComposeNonce(_sendNoncePrefix, sequence);
+            var aad = ComposeAad((uint)recordLength, sequence);
+            var cipherText = new byte[data.Length + TagSize];
+
+            try
+            {
+                var cipher = new GcmBlockCipher(AesUtilities.CreateEngine());
+                cipher.Init(true, new AeadParameters(new KeyParameter(_sendKey), TagSize * 8, nonce, aad));
+
+                var written = cipher.ProcessBytes(data, 0, data.Length, cipherText, 0);
+                written += cipher.DoFinal(cipherText, written);
+
+                if (written != cipherText.Length)
+                    throw new CryptographicException("AES-GCM produced an invalid record length.");
+
+                var record = new byte[recordLength];
+                WriteUInt64BigEndian(record, 0, sequence);
+                Buffer.BlockCopy(cipherText, 0, record, SequenceSize, cipherText.Length);
+
+                _sendSequence++;
+                return record;
+            }
+            catch (CryptoException ex)
+            {
+                throw new CryptographicException("AES-GCM record encryption failed.", ex);
+            }
+            finally
+            {
+                Clear(nonce);
+                Clear(aad);
+                Clear(cipherText);
+            }
+        }
+    }
+
+    public byte[] Decrypt(byte[] data)
+    {
+        if (data == null)
+            throw new ArgumentNullException(nameof(data));
+        if (data.Length < RecordOverhead)
+            throw new CryptographicException("The AES-GCM record is truncated.");
+
+        lock (_receiveLock)
+        {
+            ThrowIfDisposed();
+
+            var sequence = ReadUInt64BigEndian(data, 0);
+            if (sequence != _receiveSequence)
+                throw new CryptographicException("The AES-GCM record sequence is invalid.");
+
+            if (_receiveSequence == ulong.MaxValue)
+                throw new CryptographicException("The AES-GCM receive sequence is exhausted.");
+
+            var recordLength = checked((uint)data.Length);
+            var cipherTextLength = data.Length - SequenceSize;
+            var plainText = new byte[cipherTextLength - TagSize];
+            var nonce = ComposeNonce(_receiveNoncePrefix, sequence);
+            var aad = ComposeAad(recordLength, sequence);
+
+            try
+            {
+                var cipher = new GcmBlockCipher(AesUtilities.CreateEngine());
+                cipher.Init(false, new AeadParameters(new KeyParameter(_receiveKey), TagSize * 8, nonce, aad));
+
+                var written = cipher.ProcessBytes(data, SequenceSize, cipherTextLength, plainText, 0);
+                written += cipher.DoFinal(plainText, written);
+
+                if (written != plainText.Length)
+                    throw new CryptographicException("AES-GCM produced an invalid plaintext length.");
+
+                _receiveSequence++;
+                return plainText;
+            }
+            catch (CryptoException ex)
+            {
+                Clear(plainText);
+                throw new CryptographicException("AES-GCM record authentication failed.", ex);
+            }
+            catch
+            {
+                Clear(plainText);
+                throw;
+            }
+            finally
+            {
+                Clear(nonce);
+                Clear(aad);
+            }
+        }
+    }
+
+    /// <summary>
+    /// Initializes the cipher key. Session ciphers are deliberately immutable after
+    /// construction because resetting a key would also reset the GCM nonce sequence.
+    /// Create a new cipher with fresh peer nonces to use different key material.
+    /// </summary>
+    public byte[] SetKey(byte[] key)
+    {
+        ValidateSharedKey(key);
+
+        lock (_sendLock)
+        {
+            lock (_receiveLock)
+            {
+                ThrowIfDisposed();
+
+                if (_keyInitialized)
+                    throw new InvalidOperationException(
+                        "AES-GCM session keys are immutable; create a new cipher with fresh peer nonces.");
+
+                byte[] sendKey = null;
+                byte[] receiveKey = null;
+                byte[] sendNoncePrefix = null;
+                byte[] receiveNoncePrefix = null;
+
+                try
+                {
+                    sendKey = Derive(key, _contextSalt, _sendKeyLabel, KeySize);
+                    receiveKey = Derive(key, _contextSalt, _receiveKeyLabel, KeySize);
+                    sendNoncePrefix = Derive(key, _contextSalt, _sendNonceLabel, NoncePrefixSize);
+                    receiveNoncePrefix = Derive(key, _contextSalt, _receiveNonceLabel, NoncePrefixSize);
+
+                    Clear(_sendKey);
+                    Clear(_receiveKey);
+                    Clear(_sendNoncePrefix);
+                    Clear(_receiveNoncePrefix);
+
+                    _sendKey = sendKey;
+                    _receiveKey = receiveKey;
+                    _sendNoncePrefix = sendNoncePrefix;
+                    _receiveNoncePrefix = receiveNoncePrefix;
+                    sendKey = null;
+                    receiveKey = null;
+                    sendNoncePrefix = null;
+                    receiveNoncePrefix = null;
+                    _sendSequence = 0;
+                    _receiveSequence = 0;
+                    _keyInitialized = true;
+
+                    return (byte[])key.Clone();
+                }
+                finally
+                {
+                    Clear(sendKey);
+                    Clear(receiveKey);
+                    Clear(sendNoncePrefix);
+                    Clear(receiveNoncePrefix);
+                }
+            }
+        }
+    }
+
+    public void Dispose()
+    {
+        lock (_sendLock)
+        {
+            lock (_receiveLock)
+            {
+                if (_disposed)
+                    return;
+
+                _disposed = true;
+                Clear(_sendKey);
+                Clear(_receiveKey);
+                Clear(_sendNoncePrefix);
+                Clear(_receiveNoncePrefix);
+                Clear(_contextSalt);
+                _sendKey = null;
+                _receiveKey = null;
+                _sendNoncePrefix = null;
+                _receiveNoncePrefix = null;
+                _sendSequence = 0;
+                _receiveSequence = 0;
+            }
+        }
+
+        GC.SuppressFinalize(this);
+    }
+
+    static void ValidateContext(EncryptionContext context)
+    {
+        ValidateSharedKey(context.Key);
+        ValidateNonce(context.InitiatorNonce, nameof(context.InitiatorNonce));
+        ValidateNonce(context.ResponderNonce, nameof(context.ResponderNonce));
+
+        if (context.Direction != AuthenticationDirection.Initiator &&
+            context.Direction != AuthenticationDirection.Responder)
+            throw new ArgumentOutOfRangeException(nameof(context.Direction));
+
+        if (context.Mode == EncryptionMode.None)
+            throw new ArgumentException("AES-GCM requires an encrypted session mode.", nameof(context));
+        if (context.Mode != EncryptionMode.EncryptWithSessionKey &&
+            context.Mode != EncryptionMode.EncryptWithSessionKeyAndAddress)
+            throw new ArgumentOutOfRangeException(nameof(context.Mode));
+        if (string.IsNullOrWhiteSpace(context.Protocol))
+            throw new ArgumentException("A negotiated encryption protocol is required.", nameof(context));
+        if (context.OfferedProtocols == null || context.OfferedProtocols.Length == 0)
+            throw new ArgumentException("The initiator's encryption offer is required.", nameof(context));
+        if (context.OfferedProtocols.Any(string.IsNullOrWhiteSpace))
+            throw new ArgumentException("Encryption offers cannot contain empty protocol names.", nameof(context));
+        if (!context.OfferedProtocols.Contains(context.Protocol, StringComparer.Ordinal))
+            throw new ArgumentException("The selected encryption protocol was not offered.", nameof(context));
+        if (context.AuthenticationMode == AuthenticationMode.None)
+            throw new ArgumentException("AES-GCM requires an authenticated session.", nameof(context));
+        if (string.IsNullOrWhiteSpace(context.AuthenticationProtocol))
+            throw new ArgumentException("A negotiated authentication protocol is required.", nameof(context));
+
+        if (context.Mode == EncryptionMode.EncryptWithSessionKeyAndAddress)
+        {
+            ValidateAddress(context.InitiatorAddress, nameof(context.InitiatorAddress));
+            ValidateAddress(context.ResponderAddress, nameof(context.ResponderAddress));
+
+            if (IsUnspecifiedAddress(context.InitiatorAddress)
+                || IsUnspecifiedAddress(context.ResponderAddress))
+                throw new ArgumentException(
+                    "Address-bound encryption requires concrete peer network addresses.",
+                    nameof(context));
+        }
+    }
+
+    static void ValidateSharedKey(byte[] key)
+    {
+        if (key == null)
+            throw new ArgumentNullException(nameof(key));
+        if (key.Length < MinimumSharedKeySize || key.Length > MaximumSharedKeySize)
+            throw new ArgumentException(
+                $"The shared key must contain between {MinimumSharedKeySize} and {MaximumSharedKeySize} bytes.",
+                nameof(key));
+    }
+
+    static void ValidateNonce(byte[] nonce, string parameterName)
+    {
+        if (nonce == null)
+            throw new ArgumentNullException(parameterName);
+        if (nonce.Length < MinimumPeerNonceSize || nonce.Length > MaximumPeerNonceSize)
+            throw new ArgumentException(
+                $"A cipher nonce must contain between {MinimumPeerNonceSize} and {MaximumPeerNonceSize} bytes.",
+                parameterName);
+    }
+
+    static void ValidateAddress(byte[] address, string parameterName)
+    {
+        if (address == null)
+            throw new ArgumentNullException(parameterName);
+        if (address.Length != 4 && address.Length != 16)
+            throw new ArgumentException("An address must be an IPv4 or IPv6 byte sequence.", parameterName);
+    }
+
+    static byte[] ComposeContextSalt(EncryptionContext context)
+    {
+        var digest = new Sha256Digest();
+        digest.BlockUpdate(ContextLabel, 0, ContextLabel.Length);
+        digest.Update((byte)context.AuthenticationMode);
+        DigestLengthPrefixed(digest, Encoding.UTF8.GetBytes(context.AuthenticationProtocol));
+        DigestLengthPrefixed(digest, Encoding.UTF8.GetBytes(context.Domain ?? string.Empty));
+        digest.Update((byte)context.Mode);
+        DigestUInt32(digest, checked((uint)context.OfferedProtocols.Length));
+        foreach (var offeredProtocol in context.OfferedProtocols)
+            DigestLengthPrefixed(digest, Encoding.UTF8.GetBytes(offeredProtocol));
+        DigestLengthPrefixed(digest, Encoding.UTF8.GetBytes(context.Protocol));
+        DigestLengthPrefixed(digest, context.InitiatorNonce);
+        DigestLengthPrefixed(digest, context.ResponderNonce);
+
+        if (context.Mode == EncryptionMode.EncryptWithSessionKeyAndAddress)
+        {
+            DigestLengthPrefixed(digest, context.InitiatorAddress);
+            DigestLengthPrefixed(digest, context.ResponderAddress);
+        }
+
+        var salt = new byte[digest.GetDigestSize()];
+        digest.DoFinal(salt, 0);
+        return salt;
+    }
+
+    static void DigestLengthPrefixed(Sha256Digest digest, byte[] value)
+    {
+        var length = new byte[4];
+        WriteUInt32BigEndian(length, 0, checked((uint)value.Length));
+        digest.BlockUpdate(length, 0, length.Length);
+        digest.BlockUpdate(value, 0, value.Length);
+        Clear(length);
+    }
+
+    static void DigestUInt32(Sha256Digest digest, uint value)
+    {
+        var encoded = new byte[4];
+        WriteUInt32BigEndian(encoded, 0, value);
+        digest.BlockUpdate(encoded, 0, encoded.Length);
+        Clear(encoded);
+    }
+
+    static bool IsUnspecifiedAddress(byte[] address)
+        => address.All(value => value == 0);
+
+    static byte[] Derive(byte[] key, byte[] salt, byte[] label, int size)
+    {
+        var generator = new HkdfBytesGenerator(new Sha256Digest());
+        generator.Init(new HkdfParameters(key, salt, label));
+        var result = new byte[size];
+        generator.GenerateBytes(result, 0, result.Length);
+        return result;
+    }
+
+    static byte[] ComposeNonce(byte[] prefix, ulong sequence)
+    {
+        var nonce = new byte[NoncePrefixSize + SequenceSize];
+        Buffer.BlockCopy(prefix, 0, nonce, 0, NoncePrefixSize);
+        WriteUInt64BigEndian(nonce, NoncePrefixSize, sequence);
+        return nonce;
+    }
+
+    static byte[] ComposeAad(uint recordLength, ulong sequence)
+    {
+        var aad = new byte[AadSize];
+        WriteUInt32BigEndian(aad, 0, recordLength);
+        WriteUInt64BigEndian(aad, 4, sequence);
+        return aad;
+    }
+
+    static void WriteUInt32BigEndian(byte[] destination, int offset, uint value)
+    {
+        destination[offset] = (byte)(value >> 24);
+        destination[offset + 1] = (byte)(value >> 16);
+        destination[offset + 2] = (byte)(value >> 8);
+        destination[offset + 3] = (byte)value;
+    }
+
+    static void WriteUInt64BigEndian(byte[] destination, int offset, ulong value)
+    {
+        destination[offset] = (byte)(value >> 56);
+        destination[offset + 1] = (byte)(value >> 48);
+        destination[offset + 2] = (byte)(value >> 40);
+        destination[offset + 3] = (byte)(value >> 32);
+        destination[offset + 4] = (byte)(value >> 24);
+        destination[offset + 5] = (byte)(value >> 16);
+        destination[offset + 6] = (byte)(value >> 8);
+        destination[offset + 7] = (byte)value;
+    }
+
+    static ulong ReadUInt64BigEndian(byte[] source, int offset)
+        => ((ulong)source[offset] << 56)
+         | ((ulong)source[offset + 1] << 48)
+         | ((ulong)source[offset + 2] << 40)
+         | ((ulong)source[offset + 3] << 32)
+         | ((ulong)source[offset + 4] << 24)
+         | ((ulong)source[offset + 5] << 16)
+         | ((ulong)source[offset + 6] << 8)
+         | source[offset + 7];
+
+    static void Clear(byte[] value)
+    {
+        if (value != null)
+            Array.Clear(value, 0, value.Length);
+    }
+
+    void ThrowIfDisposed()
+    {
+        if (_disposed)
+            throw new ObjectDisposedException(nameof(AesGcmSymetricCipher));
+    }
+}

Libraries/Esiur/Security/Cryptography/EncryptionContext.cs

@@ -0,0 +1,55 @@
+using Esiur.Security.Authority;
+
+namespace Esiur.Security.Cryptography;
+
+/// <summary>
+/// Authenticated and negotiated material used to create a session cipher.
+/// Initiator and responder values always retain their protocol roles, regardless
+/// of which peer creates the cipher.
+/// </summary>
+public sealed class EncryptionContext
+{
+    /// <summary>Shared secret produced by the authentication provider.</summary>
+    public byte[] Key { get; set; }
+
+    /// <summary>Role of the peer creating the cipher.</summary>
+    public AuthenticationDirection Direction { get; set; }
+
+    /// <summary>Negotiated encryption mode.</summary>
+    public EncryptionMode Mode { get; set; }
+
+    /// <summary>Negotiated provider protocol name.</summary>
+    public string Protocol { get; set; }
+
+    /// <summary>
+    /// Encryption protocols offered by the initiator, in their original wire order.
+    /// Binding the complete offer prevents an intermediary from silently removing or
+    /// reordering stronger choices during negotiation.
+    /// </summary>
+    public string[] OfferedProtocols { get; set; }
+
+    /// <summary>Authentication mode that produced the shared session key.</summary>
+    public AuthenticationMode AuthenticationMode { get; set; }
+
+    /// <summary>Negotiated authentication protocol that produced the shared key.</summary>
+    public string AuthenticationProtocol { get; set; }
+
+    /// <summary>
+    /// Authentication realm/domain requested by the initiator. This is part of the
+    /// authenticated encryption transcript so credentials cannot be redirected to a
+    /// different realm that happens to derive the same shared key.
+    /// </summary>
+    public string Domain { get; set; }
+
+    /// <summary>Fresh public nonce generated by the session initiator.</summary>
+    public byte[] InitiatorNonce { get; set; }
+
+    /// <summary>Fresh public nonce generated by the session responder.</summary>
+    public byte[] ResponderNonce { get; set; }
+
+    /// <summary>Initiator address used by address-bound encryption mode.</summary>
+    public byte[] InitiatorAddress { get; set; }
+
+    /// <summary>Responder address used by address-bound encryption mode.</summary>
+    public byte[] ResponderAddress { get; set; }
+}

Libraries/Esiur/Security/Cryptography/IEncryptionProvider.cs

@@ -0,0 +1,29 @@
+namespace Esiur.Security.Cryptography;
+
+/// <summary>
+/// Creates a per-session symmetric cipher from authenticated session material.
+/// Providers are registered and negotiated by <see cref="DefaultName"/>.
+/// </summary>
+public interface IEncryptionProvider
+{
+    /// <summary>
+    /// Gets the stable protocol name advertised during connection establishment.
+    /// </summary>
+    string DefaultName { get; }
+
+    /// <summary>
+    /// Maximum number of bytes added by <see cref="ISymetricCipher.Encrypt(byte[])"/>
+    /// to one plaintext record. The transport uses this before encryption so a rejected
+    /// oversized send cannot consume a cipher sequence number.
+    /// </summary>
+    uint MaximumRecordOverhead { get; }
+
+    /// <summary>
+    /// Creates an independent authenticated record cipher for one session.
+    /// Implementations must derive independent directional keys/nonces while binding
+    /// every negotiation field in <paramref name="context"/>, authenticate each record,
+    /// reject replay/reordering, and fail closed on authentication errors. A cipher and
+    /// its nonce sequence must never be reused for another connection.
+    /// </summary>
+    ISymetricCipher CreateCipher(EncryptionContext context);
+}

Libraries/Esiur/Security/Management/IAuditingManager.cs

@@ -0,0 +1,14 @@
+using Esiur.Security.Permissions;
+
+namespace Esiur.Security.Management;
+
+/// <summary>
+/// Audits a resource operation before it is executed. A
+/// <see cref="Ruling.Denied"/> result may veto the operation, while
+/// <see cref="Ruling.Allowed"/> and <see cref="Ruling.DontCare"/> never grant
+/// authorization or override another manager's denial.
+/// </summary>
+public interface IAuditingManager : IResourceManager
+{
+    Ruling Applicable(ResourceManagerContext context);
+}

Libraries/Esiur/Security/Management/IRateControlManager.cs

@@ -0,0 +1,13 @@
+using Esiur.Security.Permissions;
+
+namespace Esiur.Security.Management;
+
+/// <summary>
+/// Evaluates whether a resource operation is admitted by rate-control policy.
+/// A manager may assign <see cref="ResourceManagerContext.Delay"/> when allowing
+/// an operation that should be queued.
+/// </summary>
+public interface IRateControlManager : IResourceManager
+{
+    Ruling Applicable(ResourceManagerContext context);
+}

Libraries/Esiur/Security/Management/IResourceManager.cs

@@ -0,0 +1,9 @@
+namespace Esiur.Security.Management;
+
+/// <summary>
+/// Identifies a manager that participates in resource operation processing.
+/// Category interfaces add the behavior appropriate to each manager type.
+/// </summary>
+public interface IResourceManager
+{
+}

Libraries/Esiur/Security/Management/ResourceManagerContext.cs

@@ -0,0 +1,66 @@
+using Esiur.Data.Types;
+using Esiur.Protocol;
+using Esiur.Resource;
+using Esiur.Security.Authority;
+using Esiur.Security.Permissions;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Esiur.Security.Management;
+
+/// <summary>
+/// Immutable metadata describing a resource operation being evaluated by managers.
+/// <see cref="Delay"/> is the sole mutable value and allows rate-control managers to
+/// request deferred execution.
+/// </summary>
+public sealed class ResourceManagerContext
+{
+    readonly IReadOnlyList<Attribute> _memberPolicyAttributes;
+
+    public Warehouse Warehouse { get; }
+    public EpConnection? Connection { get; }
+    public Session? Session { get; }
+    public IResource? Resource { get; }
+    public MemberDef? Member { get; }
+    public ActionType Action { get; }
+    public object? Inquirer { get; }
+
+    /// <summary>
+    /// Gets the local attributes that configure manager policy for the target member.
+    /// The collection is a defensive, read-only snapshot.
+    /// </summary>
+    public IReadOnlyList<Attribute> MemberPolicyAttributes => _memberPolicyAttributes;
+
+    /// <summary>
+    /// Gets or sets an optional delay requested by a rate-control manager.
+    /// </summary>
+    public TimeSpan Delay { get; set; }
+
+    public ResourceManagerContext(
+        Warehouse warehouse,
+        EpConnection? connection,
+        Session? session,
+        IResource? resource,
+        MemberDef? member,
+        ActionType action,
+        object? inquirer = null,
+        IEnumerable<Attribute>? memberPolicyAttributes = null)
+    {
+        Warehouse = warehouse ?? throw new ArgumentNullException(nameof(warehouse));
+        Connection = connection;
+        Session = session;
+        Resource = resource;
+        Member = member;
+        Action = action;
+        Inquirer = inquirer;
+
+        var policies = memberPolicyAttributes?.ToArray() ?? Array.Empty<Attribute>();
+        if (policies.Any(attribute => attribute == null))
+            throw new ArgumentException(
+                "Member policy attributes cannot contain null values.",
+                nameof(memberPolicyAttributes));
+
+        _memberPolicyAttributes = Array.AsReadOnly(policies);
+    }
+}

Libraries/Esiur/Security/Permissions/IPermissionsManager.cs

@@ -33,10 +33,11 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Esiur.Data.Types;
+using Esiur.Security.Management;
 
 namespace Esiur.Security.Permissions;
 
-public interface IPermissionsManager
+public interface IPermissionsManager : IResourceManager
 {
     /// <summary>
     /// Check for permission.

Tests/Features/Functional/Program.cs

@@ -28,6 +28,7 @@ using Esiur.Data.Types;
 using Esiur.Protocol;
 using Esiur.Resource;
 using Esiur.Security.Authority;
+using Esiur.Security.Cryptography;
 using Esiur.Security.Permissions;
 using Esiur.Security.RateLimiting;
 using Esiur.Stores;
@@ -57,6 +58,7 @@ internal static class Program
             var service = await StartServer(serverWarehouse, port);
 
             connection = await ConnectClient(clientWarehouse, port);
+            Require(connection.IsEncrypted, "Authenticated connection did not enable AES encryption.");
             var remote = await connection.Get("sys/service") as EpResource
                 ?? throw new InvalidOperationException("Remote service was not found.");
 
@@ -78,6 +80,7 @@ internal static class Program
     static async Task<MyService> StartServer(Warehouse warehouse, ushort port)
     {
         warehouse.RegisterAuthenticationProvider(new ServerAuthenticationProvider());
+        warehouse.RegisterEncryptionProvider(new AesEncryptionProvider());
         warehouse.Configuration.Parser.MaximumPacketSize = 8 * 1024 * 1024;
         warehouse.Configuration.Parser.MaximumAllocationSize = 4 * 1024 * 1024;
         warehouse.Configuration.Parser.MaximumCollectionItems = 65_536;
@@ -103,6 +106,8 @@ internal static class Program
         {
             Port = port,
             AllowedAuthenticationProviders = new[] { "hash" },
+            AllowedEncryptionProviders = new[] { AesEncryptionProvider.Name },
+            RequireEncryption = true,
         });
 
         var service = await warehouse.Put("sys/service", new MyService());
@@ -145,6 +150,7 @@ internal static class Program
     static async Task<EpConnection> ConnectClient(Warehouse warehouse, ushort port)
     {
         warehouse.RegisterAuthenticationProvider(new ClientAuthenticationProvider());
+        warehouse.RegisterEncryptionProvider(new AesEncryptionProvider());
         warehouse.Configuration.ResourceAttachments.MaximumAttachedResourcesPerConnection = 4_096;
         warehouse.Configuration.ResourceAttachments.MaximumPendingAttachmentsPerConnection = 128;
 
@@ -155,6 +161,8 @@ internal static class Program
             Identity = "tester",
             AuthenticationProtocol = "hash",
             Domain = "test",
+            EncryptionMode = EncryptionMode.EncryptWithSessionKey,
+            EncryptionProviders = new[] { AesEncryptionProvider.Name },
         });
     }
 

Tests/Features/Functional/README.md

@@ -12,7 +12,8 @@ Coverage includes:
 - rate-limit denial propagation to callers;
 - pull streams backed by `IAsyncEnumerable<T>`;
 - `TerminateExecution` through async-enumerator disposal;
-- `HaltExecution` and `ResumeExecution` for a cooperative push stream.
+- `HaltExecution` and `ResumeExecution` for a cooperative push stream;
+- AES-256-GCM provider negotiation and encrypted authenticated-session traffic;
 - parser allocation and collection budgets, attachment quotas, and per-IP connection limits.
 
 Run it from the repository root:
@@ -55,4 +56,22 @@ warehouse.Configuration.ResourceAttachments.MaximumPendingAttachmentsPerConnecti
 warehouse.Configuration.ResourceAttachments.RejectDuplicateAttachments = true;
 
 warehouse.Configuration.Connections.MaximumConnectionsPerIpAddress = 64;
+warehouse.Configuration.Encryption.MaximumRecordSize = 8 * 1024 * 1024 + 1024;
+```
+
+Authenticated encryption is opt-in and fails closed when requested. Register the
+provider on both Warehouses, allow it on the server, and request it from the client:
+
+```csharp
+serverWarehouse.RegisterEncryptionProvider(new AesEncryptionProvider());
+server.AllowedEncryptionProviders = new[] { AesEncryptionProvider.Name };
+server.RequireEncryption = true;
+
+clientWarehouse.RegisterEncryptionProvider(new AesEncryptionProvider());
+var context = new EpConnectionContext
+{
+    AuthenticationMode = AuthenticationMode.InitializerIdentity,
+    EncryptionMode = EncryptionMode.EncryptWithSessionKey,
+    EncryptionProviders = new[] { AesEncryptionProvider.Name },
+};
 ```

Tests/Unit/AesEncryptionProviderTests.cs

@@ -0,0 +1,262 @@
+using System.Reflection;
+using System.Security.Cryptography;
+using Esiur.Security.Authority;
+using Esiur.Security.Cryptography;
+
+namespace Esiur.Tests.Unit;
+
+public class AesEncryptionProviderTests
+{
+    static readonly byte[] SharedKey = Enumerable.Range(1, 64).Select(x => (byte)x).ToArray();
+    static readonly byte[] InitiatorNonce = Enumerable.Range(21, 32).Select(x => (byte)x).ToArray();
+    static readonly byte[] ResponderNonce = Enumerable.Range(91, 32).Select(x => (byte)x).ToArray();
+    static readonly byte[] InitiatorAddress = { 192, 0, 2, 10 };
+    static readonly byte[] ResponderAddress = { 198, 51, 100, 20 };
+
+    readonly AesEncryptionProvider _provider = new();
+
+    [Fact]
+    public void DefaultName_IsNegotiableProviderName()
+        => Assert.Equal("aes-gcm", _provider.DefaultName);
+
+    [Fact]
+    public void FirstRecord_MatchesStableWireVector()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        var record = initiator.Encrypt("Esiur AES-GCM vector"u8.ToArray());
+
+        Assert.Equal(
+            "0000000000000000BF5D9D7DA3D6D5232578F966450E5B96B89172D4F186A5C45299C42D8ABB732A07B1E092",
+            Convert.ToHexString(record));
+    }
+
+    [Fact]
+    public void Records_RoundTripInBothDirections()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        using var responder = Create(AuthenticationDirection.Responder);
+
+        var request = Enumerable.Range(0, 513).Select(x => (byte)x).ToArray();
+        var response = Enumerable.Range(0, 97).Select(x => (byte)(255 - x)).ToArray();
+
+        Assert.Equal(request, responder.Decrypt(initiator.Encrypt(request)));
+        Assert.Equal(response, initiator.Decrypt(responder.Encrypt(response)));
+        Assert.Empty(responder.Decrypt(initiator.Encrypt(Array.Empty<byte>())));
+    }
+
+    [Fact]
+    public void RepeatedPlaintext_UsesDistinctSequencesAndCiphertext()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        var plaintext = new byte[] { 1, 3, 3, 7 };
+
+        var first = initiator.Encrypt(plaintext);
+        var second = initiator.Encrypt(plaintext);
+
+        Assert.False(first.SequenceEqual(second));
+        Assert.Equal(new byte[8], first.Take(8).ToArray());
+        Assert.Equal(new byte[] { 0, 0, 0, 0, 0, 0, 0, 1 }, second.Take(8).ToArray());
+    }
+
+    [Fact]
+    public void DirectionalKeys_RejectReflectedRecords()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        var record = initiator.Encrypt(new byte[] { 4, 5, 6 });
+
+        Assert.Throws<CryptographicException>(() => initiator.Decrypt(record));
+    }
+
+    [Fact]
+    public void TamperedCiphertextOrTag_IsRejected()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        using var responder = Create(AuthenticationDirection.Responder);
+        var record = initiator.Encrypt(Enumerable.Range(0, 64).Select(x => (byte)x).ToArray());
+        record[record.Length - 2] ^= 0x80;
+
+        Assert.Throws<CryptographicException>(() => responder.Decrypt(record));
+    }
+
+    [Fact]
+    public void ReplayedRecord_IsRejected()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        using var responder = Create(AuthenticationDirection.Responder);
+        var record = initiator.Encrypt(new byte[] { 7, 8, 9 });
+
+        Assert.Equal(new byte[] { 7, 8, 9 }, responder.Decrypt(record));
+        Assert.Throws<CryptographicException>(() => responder.Decrypt(record));
+    }
+
+    [Fact]
+    public void OutOfOrderRecord_IsRejectedWithoutAdvancingReceiveSequence()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        using var responder = Create(AuthenticationDirection.Responder);
+        var first = initiator.Encrypt(new byte[] { 1 });
+        var second = initiator.Encrypt(new byte[] { 2 });
+
+        Assert.Throws<CryptographicException>(() => responder.Decrypt(second));
+        Assert.Equal(new byte[] { 1 }, responder.Decrypt(first));
+        Assert.Equal(new byte[] { 2 }, responder.Decrypt(second));
+    }
+
+    [Fact]
+    public void WrongSharedKey_IsRejected()
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        var wrongKey = (byte[])SharedKey.Clone();
+        wrongKey[0] ^= 0xFF;
+        using var responder = Create(AuthenticationDirection.Responder, wrongKey);
+
+        Assert.Throws<CryptographicException>(() =>
+            responder.Decrypt(initiator.Encrypt(new byte[] { 10, 20, 30 })));
+    }
+
+    [Fact]
+    public void NegotiatedProtocolName_IsBoundIntoKeyDerivation()
+    {
+        var offer = new[] { AesEncryptionProvider.Name, "aes-gcm-other" };
+        using var initiator = Create(
+            AuthenticationDirection.Initiator,
+            offeredProtocols: offer);
+        using var responder = Create(
+            AuthenticationDirection.Responder,
+            protocol: "aes-gcm-other",
+            offeredProtocols: offer);
+
+        Assert.Throws<CryptographicException>(() =>
+            responder.Decrypt(initiator.Encrypt(new byte[] { 1, 2, 3 })));
+    }
+
+    [Fact]
+    public void OriginalOfferedProtocolList_IsBoundIntoKeyDerivation()
+    {
+        using var initiator = Create(
+            AuthenticationDirection.Initiator,
+            offeredProtocols: new[] { "aes-gcm", "future-cipher" });
+        using var responder = Create(
+            AuthenticationDirection.Responder,
+            offeredProtocols: new[] { "aes-gcm" });
+
+        Assert.Throws<CryptographicException>(() =>
+            responder.Decrypt(initiator.Encrypt(new byte[] { 1, 2, 3 })));
+    }
+
+    [Theory]
+    [InlineData(AuthenticationMode.DualIdentity, "hash")]
+    [InlineData(AuthenticationMode.InitializerIdentity, "hash-v2")]
+    public void AuthenticationNegotiation_IsBoundIntoKeyDerivation(
+        AuthenticationMode responderMode,
+        string responderProtocol)
+    {
+        using var initiator = Create(AuthenticationDirection.Initiator);
+        using var responder = Create(
+            AuthenticationDirection.Responder,
+            authenticationMode: responderMode,
+            authenticationProtocol: responderProtocol);
+
+        Assert.Throws<CryptographicException>(() =>
+            responder.Decrypt(initiator.Encrypt(new byte[] { 1, 2, 3 })));
+    }
+
+    [Fact]
+    public void AuthenticationDomain_IsBoundIntoKeyDerivation()
+    {
+        using var initiator = Create(
+            AuthenticationDirection.Initiator,
+            domain: "realm-a.example");
+        using var responder = Create(
+            AuthenticationDirection.Responder,
+            domain: "realm-b.example");
+
+        Assert.Throws<CryptographicException>(() =>
+            responder.Decrypt(initiator.Encrypt(new byte[] { 1, 2, 3 })));
+    }
+
+    [Fact]
+    public void SetKey_AfterInitialization_IsRejectedForSameOrDifferentKey()
+    {
+        using var cipher = Create(AuthenticationDirection.Initiator);
+        var differentKey = (byte[])SharedKey.Clone();
+        differentKey[0] ^= 0xFF;
+
+        Assert.Throws<InvalidOperationException>(() => cipher.SetKey(SharedKey));
+        Assert.Throws<InvalidOperationException>(() => cipher.SetKey(differentKey));
+    }
+
+    [Fact]
+    public void AddressBoundMode_BindsBothPeerAddresses()
+    {
+        using var initiator = Create(
+            AuthenticationDirection.Initiator,
+            mode: EncryptionMode.EncryptWithSessionKeyAndAddress);
+        using var responder = Create(
+            AuthenticationDirection.Responder,
+            mode: EncryptionMode.EncryptWithSessionKeyAndAddress);
+
+        Assert.Equal(new byte[] { 42 }, responder.Decrypt(initiator.Encrypt(new byte[] { 42 })));
+
+        using var changedAddress = Create(
+            AuthenticationDirection.Responder,
+            mode: EncryptionMode.EncryptWithSessionKeyAndAddress,
+            responderAddress: new byte[] { 203, 0, 113, 7 });
+
+        var nextInitiator = Create(
+            AuthenticationDirection.Initiator,
+            mode: EncryptionMode.EncryptWithSessionKeyAndAddress);
+        using (nextInitiator)
+        {
+            Assert.Throws<CryptographicException>(() =>
+                changedAddress.Decrypt(nextInitiator.Encrypt(new byte[] { 42 })));
+        }
+    }
+
+    [Fact]
+    public void Dispose_ClearsDerivedSecretsAndRejectsFurtherUse()
+    {
+        var cipher = Create(AuthenticationDirection.Initiator);
+        var secretFields = new[] { "_sendKey", "_receiveKey", "_sendNoncePrefix", "_receiveNoncePrefix" }
+            .Select(name => typeof(AesGcmSymetricCipher).GetField(
+                name,
+                BindingFlags.Instance | BindingFlags.NonPublic)!)
+            .ToArray();
+        var secrets = secretFields.Select(field => (byte[])field.GetValue(cipher)!).ToArray();
+
+        Assert.All(secrets, secret => Assert.Contains(secret, value => value != 0));
+
+        cipher.Dispose();
+
+        Assert.All(secrets, secret => Assert.All(secret, value => Assert.Equal((byte)0, value)));
+        Assert.All(secretFields, field => Assert.Null(field.GetValue(cipher)));
+        Assert.Throws<ObjectDisposedException>(() => cipher.Encrypt(new byte[] { 1 }));
+    }
+
+    AesGcmSymetricCipher Create(
+        AuthenticationDirection direction,
+        byte[]? key = null,
+        EncryptionMode mode = EncryptionMode.EncryptWithSessionKey,
+        byte[]? initiatorAddress = null,
+        byte[]? responderAddress = null,
+        string protocol = AesEncryptionProvider.Name,
+        string[]? offeredProtocols = null,
+        AuthenticationMode authenticationMode = AuthenticationMode.InitializerIdentity,
+        string authenticationProtocol = "hash",
+        string domain = "example.test")
+        => (AesGcmSymetricCipher)_provider.CreateCipher(new EncryptionContext
+        {
+            Key = key ?? SharedKey,
+            Direction = direction,
+            Mode = mode,
+            Protocol = protocol,
+            OfferedProtocols = offeredProtocols ?? new[] { AesEncryptionProvider.Name },
+            AuthenticationMode = authenticationMode,
+            AuthenticationProtocol = authenticationProtocol,
+            Domain = domain,
+            InitiatorNonce = InitiatorNonce,
+            ResponderNonce = ResponderNonce,
+            InitiatorAddress = initiatorAddress ?? InitiatorAddress,
+            ResponderAddress = responderAddress ?? ResponderAddress,
+        });
+}

Tests/Unit/EncryptedRecordLimitTests.cs

@@ -0,0 +1,56 @@
+using System.Reflection;
+using Esiur.Data;
+using Esiur.Protocol;
+using Esiur.Resource;
+using Esiur.Security.Cryptography;
+
+namespace Esiur.Tests.Unit;
+
+public class EncryptedRecordLimitTests
+{
+    [Fact]
+    public void OversizedPlaintext_IsRejectedBeforeCipherSequenceIsConsumed()
+    {
+        var warehouse = new Warehouse();
+        warehouse.Configuration.Encryption.MaximumRecordSize = 32;
+        var provider = new CountingEncryptionProvider();
+        var connection = new EpConnection();
+        connection.Session.EncryptionProvider = provider;
+        connection.Session.SymetricCipher = provider.Cipher;
+
+        typeof(EpConnection)
+            .GetField("_serverWarehouse", BindingFlags.Instance | BindingFlags.NonPublic)!
+            .SetValue(connection, warehouse);
+        var compose = typeof(EpConnection)
+            .GetMethod("ComposeEncryptedRecord", BindingFlags.Instance | BindingFlags.NonPublic)!;
+
+        var error = Assert.Throws<TargetInvocationException>(() =>
+            compose.Invoke(connection, new object[] { new byte[9] }));
+
+        Assert.IsType<ParserLimitException>(error.InnerException);
+        Assert.Equal(0, provider.Cipher.EncryptCalls);
+    }
+
+    sealed class CountingEncryptionProvider : IEncryptionProvider
+    {
+        public string DefaultName => "counting";
+        public uint MaximumRecordOverhead => 24;
+        public CountingCipher Cipher { get; } = new CountingCipher();
+        public ISymetricCipher CreateCipher(EncryptionContext context) => Cipher;
+    }
+
+    sealed class CountingCipher : ISymetricCipher
+    {
+        public int EncryptCalls { get; private set; }
+        public ushort Identifier => 0;
+
+        public byte[] Encrypt(byte[] data)
+        {
+            EncryptCalls++;
+            return new byte[data.Length + 24];
+        }
+
+        public byte[] Decrypt(byte[] data) => data;
+        public byte[] SetKey(byte[] key) => key;
+    }
+}

Tests/Unit/EncryptionProviderRegistryTests.cs

@@ -0,0 +1,22 @@
+using Esiur.Resource;
+using Esiur.Security.Cryptography;
+
+namespace Esiur.Tests.Unit;
+
+public class EncryptionProviderRegistryTests
+{
+    [Fact]
+    public void Warehouse_RegistersAndResolvesEncryptionProvidersByName()
+    {
+        var warehouse = new Warehouse();
+        var provider = new AesEncryptionProvider();
+
+        warehouse.RegisterEncryptionProvider(provider);
+
+        Assert.Same(provider, warehouse.GetEncryptionProvider(AesEncryptionProvider.Name));
+        Assert.Same(provider, warehouse.TryGetEncryptionProvider(AesEncryptionProvider.Name));
+        Assert.Contains(AesEncryptionProvider.Name, warehouse.GetEncryptionProviderNames());
+        Assert.Throws<InvalidOperationException>(() =>
+            warehouse.RegisterEncryptionProvider(new AesEncryptionProvider()));
+    }
+}

Tests/Unit/EpAuthPacketTests.cs

@@ -0,0 +1,29 @@
+using Esiur.Net.Packets;
+using Esiur.Resource;
+using Esiur.Security.Authority;
+using Esiur.Security.Cryptography;
+
+namespace Esiur.Tests.Unit;
+
+public class EpAuthPacketTests
+{
+    [Theory]
+    [InlineData(AuthenticationMode.None, EncryptionMode.None)]
+    [InlineData(AuthenticationMode.InitializerIdentity, EncryptionMode.None)]
+    [InlineData(AuthenticationMode.InitializerIdentity, EncryptionMode.EncryptWithSessionKey)]
+    [InlineData(AuthenticationMode.ResponderIdentity, EncryptionMode.EncryptWithSessionKeyAndAddress)]
+    [InlineData(AuthenticationMode.DualIdentity, EncryptionMode.EncryptWithSessionKey)]
+    public void InitializeHeader_KeepsAuthenticationAndEncryptionBitsIndependent(
+        AuthenticationMode authenticationMode,
+        EncryptionMode encryptionMode)
+    {
+        var encoded = (byte)((((byte)authenticationMode & 0x3) << 2)
+                           | ((byte)encryptionMode & 0x3));
+        var packet = new EpAuthPacket(new Warehouse());
+
+        Assert.Equal(1, packet.Parse(new[] { encoded }, 0, 1));
+        Assert.Equal(EpAuthPacketCommand.Initialize, packet.Command);
+        Assert.Equal(authenticationMode, packet.AuthMode);
+        Assert.Equal(encryptionMode, packet.EncryptionMode);
+    }
+}

Tests/Unit/IndexedStructureTests.cs

@@ -90,9 +90,12 @@ public class IndexedStructureTests
         {
             Version = (byte)3,
             Domain = "example.test",
+            SupportedCiphers = new[] { "aes-gcm" },
+            CipherType = "aes-gcm",
             IPAddress = new byte[] { 127, 0, 0, 1 },
             AuthenticationProtocol = "hash",
             AuthenticationData = new byte[] { 1, 2, 3 },
+            CipherNonce = Enumerable.Range(0, 32).Select(x => (byte)x).ToArray(),
         };
 
         var bytes = Codec.ComposeIndexedType(source, Warehouse.Default, null);
@@ -100,9 +103,12 @@ public class IndexedStructureTests
         {
             [(byte)EpAuthPacketHeader.Version] = source.Version,
             [(byte)EpAuthPacketHeader.Domain] = source.Domain,
+            [(byte)EpAuthPacketHeader.SupportedCiphers] = source.SupportedCiphers,
+            [(byte)EpAuthPacketHeader.CipherType] = source.CipherType,
             [(byte)EpAuthPacketHeader.IPAddress] = source.IPAddress,
             [(byte)EpAuthPacketHeader.AuthenticationProtocol] = source.AuthenticationProtocol,
             [(byte)EpAuthPacketHeader.AuthenticationData] = source.AuthenticationData,
+            [(byte)EpAuthPacketHeader.CipherNonce] = source.CipherNonce,
         }, Warehouse.Default, null);
         var (_, raw) = Codec.ParseSync(bytes, 0, Warehouse.Default);
         var map = Assert.IsType<Map<byte, object>>(raw);
@@ -116,6 +122,9 @@ public class IndexedStructureTests
         Assert.Equal(source.IPAddress, parsed.IPAddress);
         Assert.Equal(source.AuthenticationProtocol, parsed.AuthenticationProtocol);
         Assert.Equal(source.AuthenticationData, parsed.AuthenticationData);
+        Assert.Equal(source.SupportedCiphers, parsed.SupportedCiphers);
+        Assert.Equal(source.CipherType, parsed.CipherType);
+        Assert.Equal(source.CipherNonce, parsed.CipherNonce);
     }
 
     private sealed class InvalidStructure : IndexedStructure

Tests/Unit/Integration/EncryptedEchoResource.cs

@@ -0,0 +1,10 @@
+using Esiur.Resource;
+
+namespace Esiur.Tests.Unit.Integration;
+
+[Resource]
+public partial class EncryptedEchoResource
+{
+    [Export]
+    public int Echo(int value) => value;
+}

Tests/Unit/Integration/IntegrationHarness.cs

@@ -6,6 +6,7 @@ using Esiur.Protocol;
 using Esiur.Resource;
 using Esiur.Security.Authority;
 using Esiur.Security.Authority.Providers;
+using Esiur.Security.Cryptography;
 using Esiur.Stores;
 
 namespace Esiur.Tests.Unit.Integration;
@@ -34,6 +35,50 @@ internal class TestClientAuthProvider : PasswordAuthenticationProvider
             : new IdentityPassword { Identity = null, Password = null };
 }
 
+internal sealed class OneStepAuthenticationProvider : IAuthenticationProvider
+{
+    readonly byte _keyMarker;
+
+    public OneStepAuthenticationProvider(byte keyMarker = 0)
+        => _keyMarker = keyMarker;
+
+    public string DefaultName => "one-step";
+
+    public IAuthenticationHandler CreateAuthenticationHandler(AuthenticationContext context)
+        => new OneStepAuthenticationHandler(this, _keyMarker);
+
+    public AsyncReply<bool> Login(Session session) => new AsyncReply<bool>(true);
+    public AsyncReply<bool> Logout(Session session) => new AsyncReply<bool>(true);
+}
+
+internal sealed class OneStepAuthenticationHandler : IAuthenticationHandler
+{
+    static readonly byte[] SharedKey = Enumerable.Range(1, 64).Select(x => (byte)x).ToArray();
+    readonly OneStepAuthenticationProvider _provider;
+    readonly byte _keyMarker;
+
+    public OneStepAuthenticationHandler(OneStepAuthenticationProvider provider, byte keyMarker)
+    {
+        _provider = provider;
+        _keyMarker = keyMarker;
+    }
+
+    public IAuthenticationProvider Provider => _provider;
+    public string Protocol => _provider.DefaultName;
+
+    public AuthenticationResult Process(object authData)
+    {
+        var key = (byte[])SharedKey.Clone();
+        key[0] ^= _keyMarker;
+        return new AuthenticationResult(
+            AuthenticationRuling.Succeeded,
+            null,
+            "tester",
+            "server",
+            key);
+    }
+}
+
 /// <summary>
 /// Spins up an in-process Esiur server and an authenticated client connection over loopback TCP,
 /// so the real socket + protocol + FetchResource stack is exercised end to end. Each instance
@@ -61,18 +106,37 @@ internal sealed class IntegrationCluster : IAsyncDisposable
     /// Builds a server hosting resources under "sys/&lt;rootPath&gt;" populated by
     /// <paramref name="populate"/>, opens it, then connects an authenticated client.
     /// </summary>
-    public static async Task<IntegrationCluster> StartAsync(Func<Warehouse, Task> populate)
+    public static async Task<IntegrationCluster> StartAsync(
+        Func<Warehouse, Task> populate,
+        bool encrypted = false,
+        bool requireEncryption = false,
+        EncryptionMode encryptionMode = EncryptionMode.EncryptWithSessionKey,
+        bool allowEncryption = true,
+        bool oneStepAuthentication = false,
+        bool useWebSocket = false,
+        bool mismatchedSessionKeys = false)
     {
         var port = Interlocked.Increment(ref _portCounter);
 
         var serverWh = new Warehouse();
-        serverWh.RegisterAuthenticationProvider(new TestServerAuthProvider());
+        serverWh.RegisterAuthenticationProvider(oneStepAuthentication
+            ? new OneStepAuthenticationProvider()
+            : new TestServerAuthProvider());
+        if (encrypted || requireEncryption)
+            serverWh.RegisterEncryptionProvider(new AesEncryptionProvider());
 
         await serverWh.Put("sys", new MemoryStore());
         var server = await serverWh.Put("sys/server", new EpServer
         {
             Port = (ushort)port,
-            AllowedAuthenticationProviders = new[] { "hash" },
+            AllowedAuthenticationProviders = new[]
+            {
+                oneStepAuthentication ? "one-step" : "hash",
+            },
+            AllowedEncryptionProviders = (encrypted || requireEncryption) && allowEncryption
+                ? new[] { AesEncryptionProvider.Name }
+                : Array.Empty<string>(),
+            RequireEncryption = requireEncryption,
         });
 
         await populate(serverWh);
@@ -81,18 +145,38 @@ internal sealed class IntegrationCluster : IAsyncDisposable
 
         var cluster = new IntegrationCluster(serverWh, server, port);
 
-        cluster.ClientWarehouse.RegisterAuthenticationProvider(new TestClientAuthProvider());
+        cluster.ClientWarehouse.RegisterAuthenticationProvider(oneStepAuthentication
-        cluster.Connection = await cluster.ClientWarehouse.Get<EpConnection>(
+            ? new OneStepAuthenticationProvider(mismatchedSessionKeys ? (byte)0x80 : (byte)0)
-            $"ep://localhost:{port}",
+            : new TestClientAuthProvider());
-            new EpConnectionContext
+        if (encrypted)
-            {
+            cluster.ClientWarehouse.RegisterEncryptionProvider(new AesEncryptionProvider());
-                AuthenticationMode = AuthenticationMode.InitializerIdentity,
-                Identity = "tester",
-                AuthenticationProtocol = "hash",
-                Domain = "test",
-            });
 
-        return cluster;
+        try
+        {
+            cluster.Connection = await cluster.ClientWarehouse.Get<EpConnection>(
+                $"ep://localhost:{port}",
+                new EpConnectionContext
+                {
+                    AuthenticationMode = AuthenticationMode.InitializerIdentity,
+                    Identity = "tester",
+                    AuthenticationProtocol = oneStepAuthentication ? "one-step" : "hash",
+                    Domain = "test",
+                    EncryptionMode = encrypted
+                        ? encryptionMode
+                        : EncryptionMode.None,
+                    EncryptionProviders = new[] { AesEncryptionProvider.Name },
+                    UseWebSocket = useWebSocket,
+                });
+
+            return cluster;
+        }
+        catch
+        {
+            try { server.Destroy(); } catch { }
+            try { await cluster.ClientWarehouse.Close(); } catch { }
+            try { await serverWh.Close(); } catch { }
+            throw;
+        }
     }
 
     public async ValueTask DisposeAsync()

Tests/Unit/Integration/SessionHeadersIntegrationTests.cs

@@ -1,5 +1,10 @@
 namespace Esiur.Tests.Unit.Integration;
 
+using Esiur.Data;
+using Esiur.Net.Sockets;
+using Esiur.Protocol;
+using Esiur.Security.Cryptography;
+
 [Collection("Integration")]
 public class SessionHeadersIntegrationTests
 {
@@ -19,4 +24,168 @@ public class SessionHeadersIntegrationTests
         Assert.Equal("hash", serverConnection.Session.RemoteHeaders.AuthenticationProtocol);
         Assert.Null(serverConnection.Session.RemoteHeaders.AuthenticationData);
     }
+
+    [Fact]
+    public async Task AuthenticatedHandshake_NegotiatesAesAndEncryptsApplicationTraffic()
+    {
+        await using var cluster = await IntegrationCluster
+            .StartAsync(
+                async warehouse =>
+                {
+                    await warehouse.Put("sys/encrypted", new Node { Id = 42 });
+                },
+                encrypted: true)
+            .WaitAsync(TimeSpan.FromSeconds(10));
+
+        var serverConnection = Assert.Single(cluster.Server.Connections);
+
+        Assert.True(cluster.Connection.IsEncrypted);
+        Assert.True(serverConnection.IsEncrypted);
+        Assert.Equal(EncryptionMode.EncryptWithSessionKey,
+                     cluster.Connection.Session.EncryptionMode);
+        Assert.Equal(AesEncryptionProvider.Name,
+                     cluster.Connection.Session.RemoteHeaders.CipherType);
+        Assert.Equal(AesEncryptionProvider.Name,
+                     serverConnection.Session.LocalHeaders.CipherType);
+        Assert.NotNull(cluster.Connection.Session.SymetricCipher);
+        Assert.NotNull(serverConnection.Session.SymetricCipher);
+        Assert.Null(cluster.Connection.Session.LocalHeaders.CipherKey);
+        Assert.Null(cluster.Connection.Session.RemoteHeaders.CipherKey);
+
+        // Fetch crosses the protected record layer in both directions.
+        Assert.NotNull(await Task.Run(async () =>
+            await cluster.Connection.Get("sys/encrypted"))
+            .WaitAsync(TimeSpan.FromSeconds(10)));
+    }
+
+    [Fact]
+    public async Task ServerRequiredEncryption_RejectsPlaintextWithoutDowngrade()
+    {
+        await Assert.ThrowsAnyAsync<Exception>(async () =>
+            await IntegrationCluster
+                .StartAsync(
+                    _ => Task.CompletedTask,
+                    encrypted: false,
+                    requireEncryption: true)
+                .WaitAsync(TimeSpan.FromSeconds(10)));
+    }
+
+    [Fact]
+    public async Task AddressBoundEncryption_DerivesMatchingCiphersAcrossPeers()
+    {
+        await using var cluster = await IntegrationCluster
+            .StartAsync(
+                async warehouse =>
+                {
+                    await warehouse.Put("sys/address-bound", new Node { Id = 7 });
+                },
+                encrypted: true,
+                encryptionMode: EncryptionMode.EncryptWithSessionKeyAndAddress)
+            .WaitAsync(TimeSpan.FromSeconds(10));
+
+        Assert.True(cluster.Connection.IsEncrypted);
+        Assert.Equal(EncryptionMode.EncryptWithSessionKeyAndAddress,
+                     cluster.Connection.Session.EncryptionMode);
+        Assert.NotNull(await Task.Run(async () =>
+            await cluster.Connection.Get("sys/address-bound"))
+            .WaitAsync(TimeSpan.FromSeconds(10)));
+    }
+
+    [Fact]
+    public async Task DisallowedEncryptionProvider_FailsWithoutPlaintextFallback()
+    {
+        await Assert.ThrowsAnyAsync<Exception>(async () =>
+            await IntegrationCluster
+                .StartAsync(
+                    _ => Task.CompletedTask,
+                    encrypted: true,
+                    allowEncryption: false)
+                .WaitAsync(TimeSpan.FromSeconds(10)));
+    }
+
+    [Fact]
+    public async Task OneStepAuthentication_ConfirmsEncryptionBeforeFetchAndRpc()
+    {
+        await using var cluster = await IntegrationCluster
+            .StartAsync(
+                async warehouse =>
+                {
+                    await warehouse.Put("sys/one-step-encrypted", new EncryptedEchoResource());
+                },
+                encrypted: true,
+                oneStepAuthentication: true)
+            .WaitAsync(TimeSpan.FromSeconds(10));
+
+        var remote = (EpResource)await Task.Run(async () =>
+            await cluster.Connection.Get("sys/one-step-encrypted"))
+            .WaitAsync(TimeSpan.FromSeconds(10));
+        var function = remote.Instance.Definition
+            .GetFunctionDefByName(nameof(EncryptedEchoResource.Echo));
+        var result = await remote._Invoke(
+            function.Index,
+            new Map<byte, object> { [0] = 117 });
+
+        Assert.True(cluster.Connection.Session.Authenticated);
+        Assert.True(cluster.Connection.IsEncrypted);
+        var serverConnection = Assert.Single(cluster.Server.Connections);
+        Assert.True(serverConnection.Session.Authenticated);
+        Assert.True(serverConnection.IsEncrypted);
+        Assert.Equal(117, Convert.ToInt32(result));
+    }
+
+    [Fact]
+    public async Task WebSocketTransport_EncryptsFetchAndRpc()
+    {
+        await using var cluster = await IntegrationCluster
+            .StartAsync(
+                async warehouse =>
+                {
+                    await warehouse.Put("sys/websocket-encrypted", new EncryptedEchoResource());
+                },
+                encrypted: true,
+                useWebSocket: true)
+            .WaitAsync(TimeSpan.FromSeconds(10));
+
+        var remote = (EpResource)await Task.Run(async () =>
+            await cluster.Connection.Get("sys/websocket-encrypted"))
+            .WaitAsync(TimeSpan.FromSeconds(10));
+        var function = remote.Instance.Definition
+            .GetFunctionDefByName(nameof(EncryptedEchoResource.Echo));
+        var result = await remote._Invoke(
+            function.Index,
+            new Map<byte, object> { [0] = 203 });
+
+        Assert.True(cluster.Connection.IsEncrypted);
+        Assert.IsType<FrameworkWebSocket>(cluster.Connection.Socket);
+        Assert.True(Assert.Single(cluster.Server.Connections).IsEncrypted);
+        Assert.Equal(203, Convert.ToInt32(result));
+    }
+
+    [Fact]
+    public async Task WrongAuthenticatedSessionKey_FailsPromptlyDuringKeyConfirmation()
+    {
+        var exception = await Assert.ThrowsAnyAsync<Exception>(async () =>
+            await IntegrationCluster.StartAsync(
+                    _ => Task.CompletedTask,
+                    encrypted: true,
+                    oneStepAuthentication: true,
+                    mismatchedSessionKeys: true)
+                .WaitAsync(TimeSpan.FromSeconds(5)));
+
+        Assert.IsNotType<TimeoutException>(exception);
+    }
+
+    [Fact]
+    public async Task AddressBoundEncryption_RejectsWebSocketWithoutConcreteEndpoints()
+    {
+        var exception = await Assert.ThrowsAnyAsync<Exception>(async () =>
+            await IntegrationCluster.StartAsync(
+                    _ => Task.CompletedTask,
+                    encrypted: true,
+                    encryptionMode: EncryptionMode.EncryptWithSessionKeyAndAddress,
+                    useWebSocket: true)
+                .WaitAsync(TimeSpan.FromSeconds(5)));
+
+        Assert.IsNotType<TimeoutException>(exception);
+    }
 }