## What
- Bind the login auth id to the account **and** origin address that earned it, make it a CSPRNG draw, expire it after two minutes, and spend it only once its owner presents it.
- Skip the password verify on `GameLogin` (0x91) when the presented id vouches for the submitted username and address.
## Why
A full client login hashes the password twice — `AccountLogin` (0x80) and then `GameLogin` (0x91). At the current Argon2 parameters that is **most of a 16 ms frame each, on the single-threaded game loop**, for every login attempt.
The second verify is redundant. `GameLogin` already requires an id from `_authIDWindow`, and that window is only populated by `GenerateAuthID`, called from `PlayServer` — reachable only after 0x80 has already authenticated the account **in this same process**. ModernUO Gateway has its own auth-id passing mechanism and is out of scope here.
## Why the id needed hardening first
Skipping the verify promotes the id from a correlation token to a bearer token, and it was not one:
- drawn from `Utility.Random` → `BuiltInRng`, a non-cryptographic PRNG
- bound to nothing — `AuthIDPersistence` carried only `Age` and `Version`
- never expiring; `Age` was only read to pick an eviction victim
A guessed id got you nothing while the password was still checked. Without that check it would have been an account takeover, so the id is now a CSPRNG draw, single-use, two-minute TTL, and bound to both the account and the origin address.
What remains is observing a live id on the client's network or machine — which the server cannot defend against under any design, and which already yields the password itself, since the client transmits it in the same handshake.
Network switching mid-login is deliberately unsupported.
## Behaviour
A full verify was always required before this change, and ids never expired, so every "before" is a password check.
| Case | Before | After |
|---|---|---|
| Id absent | Disconnect | Disconnect |
| Address mismatch | Verify | **Disconnect** |
| Account mismatch | Verify | **Disconnect** |
| Expired | Verify | **Verify** |
| Id vouches | Verify | **Skip** |
No case grants access the previous code would have denied. Expiry deliberately falls back to the verify rather than disconnecting — a player can idle, and turning that into a lockout would be a regression for no gain.
## Look, then take
An id is not consumed until the presenter has shown it is theirs. Removing it first would let anyone who lands on a live id burn it, and its owner would arrive to `"Unable to find auth id."` and have to log in again over a packet they had no part in.
The **address is compared before the account**, so a guesser from anywhere else is rejected before a username is ever looked at. That is what makes it safe to leave the id in place on a mismatch: there is no username-enumeration risk to trade against, and the only presenter who could enumerate is already on the victim's own address.
## The window is not a cap
It was 128 entries with the oldest evicted to make room. That is a cap on *concurrent logins*, not a resource bound: 800 people picking a server at once would have live ids discarded and those clients would arrive to `"Unable to find auth id."` — a failed login caused by nothing except other people logging in.
Issuing now sweeps expired entries and lets the window grow if everything in it is still live. Unbounded is safe here: an entry costs a **successful** password verify to create and dies after two minutes, so its size tracks logins genuinely in flight.
Removing an id when its connection drops is not an option, and this was checked rather than assumed — `NetState.cs:787` disconnects the login connection *deliberately*, immediately after the id is issued, and that disconnect is never cancelled. Surviving it is the whole purpose of the id. Expiry is the only correct reclamation.
## Handshake hardening
Choosing a server queues a disconnect, but the queue drains on the *next* slice, so a client pipelining into the same recv buffer can reach the handshake handlers again. Two had no do-once guard:
- `LoginServerSeed` (0xEF) now rejects when `state.Seeded` is already set.
- `PlayServer` (0xA0) now rejects when `state.AuthId != 0` — otherwise a connection that had already spent its id would be handed the spent one back.
Issuing is also idempotent (`EnsureAuthId`), so a connection holds exactly one id by construction and an orphan is impossible rather than something to clean up. The login state machine itself is untouched.
Also fixes a fall-through: the "Unable to find auth id" branch disconnected without returning, then continued with a default entry and nulled `state.Version`.
## Testing
`ConsumeAuthId` is a seam with no `NetState` dependency, so the auth decision is tested directly: vouching, account mismatch, address mismatch, case-insensitive usernames, IPv4-mapped-IPv6, unknown ids, single-use by the owner, **a rejected attempt leaving the id redeemable**, expiry-into-verify, and an 800-id login rush that must evict nobody. Expiry is driven by moving `Core._now`, not by waiting. Every new clause was verified to discriminate by removing it and confirming only its own tests fail.
## Cost
Halves the per-login game-loop cost. This does not make hashing cheaper or move it off the loop — that is gated on a measurement described in `docs/handoffs/2026-08-07-off-loop-argon2-hashing.md`.
> [!IMPORTANT]
> **Breaking Changes**
> - DecodePacket and EncodePacket delegates replaced with IClientEncryption interface
> - NetState.Connection (Socket) replaced with internal RingSocket management
> - NetState.RecvPipe and NetState.SendPipe removed (buffers managed internally)
## Summary
Upgrades the networking stack from PollGroup-based I/O to io_uring, significantly improving I/O performance on Linux.
This also adds native client encryption support for encrypted UO clients.
## Major Changes
io_uring Networking Architecture
- Replaced PollGroup with IORingGroup for async socket I/O operations
- Removed Pipe.cs (mirrored ring buffer) and TcpServer.cs in favor of RingSocketManager
- Added NetState.Network.cs - centralized network infrastructure handling accept, recv, send, and disconnect
completions
- Added SocketHelper.cs - platform-specific socket utilities for raw socket handle operations (getpeername,
getsockname)
- Buffer management now handled by RingSocketManager with configurable slab allocation
### Client Encryption Support
- Added full encryption stack in Network/Encryption/:
- EncryptionConfig.cs - configurable encryption modes (None, Unencrypted, Encrypted, Both)
- EncryptionManager.cs - encryption detection and initialization for login/game packets
- LoginEncryption.cs - handles login packet encryption with version-derived keys
- GameEncryption.cs - handles game server encryption using Twofish
- TwofishEngine.cs - optimized Twofish block cipher implementation
- LoginKeys.cs - encryption key table for client versions
- IClientEncryption.cs - interface for client encryption implementations
### NetState Improvements
- Replaced Socket Connection with RingSocket _socket for managed socket lifecycle
- Changed from GCHandle polling to event-based completion processing
- Disconnect handling now properly waits for pending sends to flush
- Simplified connecting socket management using lazy queue removal
### Configuration
- New settings: network.encryptionMode and network.encryptionDebug
- Encryption mode flags: Unencrypted, Encrypted, or Both
### Dependencies
- Replaced PollGroup NuGet package with IORingGroup
- Linux requires liburing-dev / liburing-devel package
### Test plan
- Verify server starts and accepts connections on Linux with io_uring
- Verify server starts and accepts connections on Windows (fallback to IOCP)
- Test unencrypted client connections (ClassicUO with encryption disabled)
- Test encrypted client connections if available
- Verify graceful disconnect flushes pending data
- Confirm CI builds pass on all target platforms
> [!Note]
> **Developer Note**
> Now developers will only need to build/run the Application project instead of everything.
> When adding new projects, make sure to:
> 1. Add a reference to that project in the Application project.
> 2. Add the dll file to the Distribution/Data/assemblies.json file
### Summary
- Adds an application project
- Consolidates process restarts to use `Core.Kill(true)`
- Removes some old messaging, for example processor optimization
- Fixes missing build cleanup
## Breaking Changes
Incoming packet registration signature has changed to:
```cs
delegate* void OnReceiveCallback(NetState state, SpanReader reader, int packetLength);
IncomingPackets.Register(int packetID, int length, bool ingame, OnReceiveCallback onReceive);
```
For example, an incoming packet handler signature would now look like this:
```cs
public static void SomeIncomingPacket(NetState state, SpanReader reader, int packetLength)
{
// Parse the data
}
```
## Summary
Updates the network Pipe class to use a mirrored memory technique. This technique involves mapping the same physical memory to two contiguous virtual memory spaces so the byte buffer appears duplicated. This allows writing to a double-sized array to wrap around without the need for the `CircularBuffer` classes.
In practice this allows us to use `Span<byte>` as if the buffer was a regular array.
### Bug Fixes
- [X] Fixes bad fixed length string parsing
- [X] Caches DateTime.NowUtc on the game loop (not other threads)
- [X] Replaces all locations where it makes sense
- [X] Adds Min/Max for `IComparable` (TimeSpan, DateTimes, etc)
Closes#261
- [X] Removes some string allocations (e.g. split)
- [X] Optimizes some collections
- [X] Converts insensitive to extension methods of built-ins.
- [X] Adds ordinal (case sensitive) string helpers
- [X] Fixes conditionals for in-game commands so they use Ordinal comparisons.
- [X] Replaces ToLower.Contains with InsensitiveContains
- [X] Adds ValueStringBuilder
- [X] Implements ValueStringBuilder in a few places where it makes sense
- [X] Removes the redundant Wrap function and replaces it with an optimized version
- [X] Fixes list conversions in Utility
Closes#351
Bumps release version
