sslpsk

This module adds TLS-PSK support to the Python 2.7 and 3.x ssl package. Simply use

sslpsk.wrap_socket(sock, psk=b'...', ...)

instead of

ssl.wrap_socket(sock, ...)

Installation

pip install sslpsk

pip builds from source for Linux and Mac OSX, so a C compiler, the Python development headers, and the openSSL development headers are required. For Microsoft Windows, pre-built binaries are available so there are no such prerequisites.

Usage

sslpsk.wrap_socket(...) is a drop-in replacement for ssl.wrap_socket(...) that supports two additional arguments, psk and hint.

psk sets the preshared key and, optionally, the identity for a client connection. hint sets the identity hint for a server connection and is optional.

For client connections, psk can be one of four things:

1. Just the preshared key.

sslpsk.wrap_socket(sock, psk=b'mypsk')

2. A tuple of the preshared key and client identity.

sslpsk.wrap_socket(sock, psk=(b'mypsk', b'myidentity'))

3. A function mapping the server identity hint to the preshared key.

PSK_FOR = {b'server1' : b'abcdef',
           b'server2' : b'123456'}

sslpsk.wrap_socket(sock, psk=lambda hint: PSK_FOR[hint])

4. A function mapping the server identity hint to a tuple of the preshared key and client identity.

PSK_FOR = {b'server1' : b'abcdef',
           b'server2' : b'123456'}

ID_FOR  = {b'server1' : b'clientA',
           b'server2' : b'clientB'}

sslpsk.wrap_socket(sock, psk=lambda hint: (PSK_FOR[hint], ID_FOR[hint]))

For server connections, psk can be one of two things:

1. Just the preshared key.

sslpsk.wrap_socket(sock, server_side=True, psk=b'mypsk')

2. A function mapping the client identity to the preshared key.

PSK_FOR = {b'clientA' : b'abcdef',
           b'clientB' : b'123456'}

sslpsk.wrap_socket(sock, server_side=True, psk=lambda identity: PSK_FOR[identity])

Additionally for server connections, the optional server identity hint is specified using the hint argument.

sslpsk.wrap_socket(sock, server_side=True, hint=b'myidentity', psk=b'mypsk')

If hint is not specified, None, or the empty string, the identity hint will not be sent to the client.

Example Server

from __future__ import print_function
import socket
import ssl
import sslpsk

PSKS = {'client1' : 'abcdef',
        'client2' : '123456'}

def server(host, port):
    tcp_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    tcp_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    tcp_sock.bind((host, port))
    tcp_sock.listen(1)

    sock, _ = tcp_sock.accept()
    ssl_sock = sslpsk.wrap_socket(sock,
                                  server_side = True,
                                  ssl_version=ssl.PROTOCOL_TLSv1,
                                  ciphers='ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH',
                                  psk=lambda identity: PSKS[identity],
                                  hint=b'server1')

    msg = ssl_sock.recv(4).decode()
    print('Server received: %s'%(msg))
    msg = "pong"
    ssl_sock.sendall(msg.encode())

    ssl_sock.shutdown(socket.SHUT_RDWR)
    ssl_sock.close()

def main():
    host = '127.0.0.1'
    port = 6000
    server(host, port)

if __name__ == '__main__':
    main()

Example Client

from __future__ import print_function
import socket
import ssl
import sslpsk

PSKS = {b'server1' : b'abcdef',
        b'server2' : b'uvwxyz'}

def client(host, port, psk):
    tcp_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    tcp_socket.connect((host, port))

    ssl_sock = sslpsk.wrap_socket(tcp_socket,
                                  ssl_version=ssl.PROTOCOL_TLSv1,
                                  ciphers='ALL:!ADH:!LOW:!EXP:!MD5:@STRENGTH',
                                  psk=lambda hint: (PSKS[hint], b'client1'))

    msg = "ping"
    ssl_sock.sendall(msg.encode())
    msg = ssl_sock.recv(4).decode()
    print('Client received: %s'%(msg))

    ssl_sock.shutdown(socket.SHUT_RDWR)
    ssl_sock.close()

def main():
    host = '127.0.0.1'
    port = 6000
    client(host, port, PSKS)

if __name__ == '__main__':
    main()

Changelog

• 0.1.0 (July 31, 2017)
  • initial release
• 1.0.0 (August 2, 2017)
  • include tests in pip distribution
  • add support for Windows

Acknowledgments

The main approach was borrowed from webgravel/common-ssl.

Contributing

Please submit bugs, questions, suggestions, or (ideally) contributions as issues and pull requests on GitHub.

Maintainers

David R. Bild

• https://www.davidbild.org
• https://github.com/drbild

License

Copyright 2017 David R. Bild

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this work except in compliance with the License. You may obtain a copy of the License from the LICENSE.txt file or at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.