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) are encrypted using double-ratchet algorithm, providing forward secrecy and break-in recovery. This layer uses two Curve448 keys per client for X3DH key agreement, 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 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.
• SimpleX chat v1 announcement.

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 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):
    • 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