# 1.0.0

Security and privacy improvements:
- Faster and more secure 2-layer E2E encryption with additional encryption layer between servers and recipients:
  - application messages in each duplex connection (managed by SMP agents - see [overview](https://github.com/simplex-chat/simplexmq/blob/master/protocol/overview-tjr.md)) are encrypted using [double-ratchet algorithm](https://www.signal.org/docs/specifications/doubleratchet/), providing forward secrecy and break-in recovery. This layer uses two Curve448 keys per client for [X3DH key agreement](https://www.signal.org/docs/specifications/x3dh/), SHA512 based HKDFs and AES-GCM AEAD encryption.
  - SMP client messages are additionally E2E encrypted in each SMP queue to avoid cipher-text correlation of messages sent via multiple redundant queues (that will be supported soon). This and the next layer use [NaCl crypto_box algorithm](https://nacl.cr.yp.to/index.html) with XSalsa20Poly1305 cipher and Curve25519 keys for DH key agreement.
  - Messages delivered from the servers to the recipients are additionally encrypted to avoid cipher-text correlation between sent and received messages.
- To prevent any traffic correlation by content size, SimpleX uses fixed transport block size of 16kb (16384 bytes) with padding on all encryption layers:
  - application messages are padded to 15788 bytes before E2E double-ratchet encryption.
  - messages between SMP clients are padded to 16032 bytes before E2E encryption in each SMP queue.
  - messages from the server to the recipient are padded to padded to 16088 bytes before the additional encryption layer (see above).
- TLS 1.2+ with tls-unique channel binding in each command to prevent replay attacks.
- Server identity verification via server offline certificate fingerprints included in SMP server addresses.

New functionality:
- Support for notification servers with new SMP commands: `NKEY`/`NID`, `NSUB`/`NMSG`.

Efficiency improvements:
- Binary protocol encodings to reduce overhead from circa 15% to approximately 3.7% of transmitted application message size, with only 2.2% overhead for SMP protocol messages.
- More performant cryptographic algorithms.

For more information about SimpleX:
- [SimpleX overview](https://github.com/simplex-chat/simplexmq/blob/master/protocol/overview-tjr.md).
- [SimpleX chat v1 announcement](https://github.com/simplex-chat/simplex-chat/blob/master/blog/20220112-simplex-chat-v1-released.md).

# 0.5.2

- Fix message delivery logic that blocked delivery of all server messages when server per-queue quota exceeded, making it concurrent per SMP queue, not per server.

# 0.5.1

- Fix server subscription logic bug that was leading to memory leak / resource exhaustion in some edge cases.

# 0.5.0

- No changes in SMP server implementation - it is backwards compatible with v0.4.1
- SMP agent changes:
  - URI syntax for SMP queues and connection requests.
  - long-term connections links ("contacts") in SMP agent protocol.
  - agent command changes:
    - `REQ` notification and `ACPT` command are used only with long-term connection links.
    - `CONF` notification and `LET` commands are used for normal duplex connections.

# 0.4.1

- Include migrations in the package

# 0.4.0

- SMP server implementation and [SMP protocol](https://github.com/simplex-chat/simplexmq/blob/master/protocol/simplex-messaging.md) changes:
  - support 3072 bit RSA key size
  - add SMP queue quotas
  - set default transport block size to 4096 bits
  - allow SMP client to change transport block size during transport connection handshake
- SMP agent implementation and protocol changes:
  - additional connection confirmation step for initiating party
  - automatically resume subscribed duplex connections once transport connection is resumed
  - passing an arbitrary binary information between parties during the duplex connection handshake - can be used to identify parties
  - asynchronous duplex connection handshake - the parties do not have to be online at the same time
  - asynchronous message delivery - the agent does not need transport connection to accept client messages for delivery
  - additional confirmation of message reception from the client to prevent message loss in case of process termination
  - set transport block size to 8192 bits (in the future the agent protocol can allow to have different block sizes for different duplex connections)
  - added client commands and notifications (see [agent protocol](https://github.com/simplex-chat/simplexmq/blob/master/protocol/agent-protocol.md)):
    - `REQ` - the notification about joining party establishing connection
    - `ACPT` - the command to accept connection with the joining party
    - `INFO` - the notification with the information from the initiating party
    - `DOWN`/`UP` - the notifications about losing/resuming the connection
    - `ACK` - the command to confirm that the message reception/processing is complete
    - `MID` - the response to `SEND` confirming that the message is accepted by the agent
    - `MERR` - the notification about permanent message delivery error (e.g., `ERR AUTH` indicating that the queue was removed)

# 0.3.2

- Support websockets
- SMP server CLI commands

# 0.3.1

- Released to hackage.org
- SMP agent protocol changes:
  - move SMP server from agent commands NEW/JOIN to agent config
  - send CON to user only when the 1st party responds HELLO
- Fix REPLY vulnerability
- Fix transaction busy error

# 0.3.0

- SMP encrypted transport over TCP
- Standard X509/PKCS8 encoding for RSA keys
- Sign and verify agent messages
- Verify message integrity based on previous message hash and ID
- Prevent timing attack allowing to determine if queue exists
- Only allow correct RSA keys and signature sizes

# 0.2.0

- SMP client library
- SMP agent with E2E encryption

# 0.1.0

- SMP protocol server implementation without encryption