PSSST: Packet Security for Stateless Server Transactions

This module implements the PSSST protocol and provides a very simple interface for client and server endpoints. PSSST is designed to provide a light weight way for clients to securely communicate with servers.

Using the pssst library is very simple. A client is represented by an instance of the PSSSTClient class which is instantiated with the server’s public key and optionally specifies the client’s private key and the cipher suite. A server is represented by an instance of the PSSSTServer class which is instantiated with the server’s private key and optionally specifies the cipher suite. Each of these classes offer only one method.

The PSSSTClient class provides the pack_request() method; this takes the request message as its sole argument and returns a tuple of the encrypted and packed packet and a function that can be used to unpack the reply to that packet.

The PSSSTServer class provides the unpack_request() method; this takes an encrypted request packet as its sole argument and returns a tuple containing the decrypted request message, the authenticated client public key (or None if client authentication is not used) and a function that can be used to pack the reply message into an encrypted packet. Thus a minimal example of a transaction is as follows:

client = pssst.PSSSTClient(server_public_key)
server = pssst.PSSSTServer(server_private_key)

request_message = b"The Magic Words are Squeamish Ossifrage"

# Pack the message with the client and unpack it with the server
request_packet, client_reply_handler = client.pack_request(request_message)
received_request, client_auth_key, server_reply_handler = server.unpack_request(request_packet)

# Echo the request back from the server to the client
reply_packet = server_reply_handler(received_request)
received_reply = client_reply_handler(reply_packet)