> srptools get_user_data_triplet
> srptools server get_private_and_public
> srptools client get_private_and_public
> srptools client get_session_data
> srptools server get_session_data

Help is available:

.. code-block::

> srptools --help

API usage

Preliminary step. Agree on communication details:

.. code-block:: python

from srptools import SRPContext

context = SRPContext('alice', 'password123')
username, password_verifier, salt = context.get_user_data_triplet()
prime = context.prime
gen = context.generator

Simplified workflow:

.. code-block:: python

from srptools import SRPContext, SRPServerSession, SRPClientSession

# Receive username from client and generate server public.
server_session = SRPServerSession(SRPContext(username, prime=prime, generator=gen), password_verifier)
server_public = server_session.public

# Receive server public and salt and process them.
client_session = SRPClientSession(SRPContext('alice', 'password123', prime=prime, generator=gen))
client_session.process(server_public, salt)
# Generate client public and session key.
client_public = client_session.public

# Process client public and compare session keys.
server_session.process(client_public, salt)

assert server_session.key == client_session.key

Extended workflow

.. code-block:: python

from srptools import SRPContext, SRPServerSession, SRPClientSession

# Receive username from client and generate server public.
server_session = SRPServerSession(SRPContext(username, prime=prime, generator=gen), password_verifier)
server_public = server_session.public

# Receive server public and salt and process them.
client_session = SRPClientSession(SRPContext('alice', 'password123', prime=prime, generator=gen))
client_session.process(server_public, salt)
# Generate client public and session key proof.
client_public = client_session.public
client_session_key_proof = client_session.key_proof

# Process client public and verify session key proof.
server_session.process(client_public, salt)
assert server_session.verify_proof(client_session_key_proof)
# Generate session key proof hash.
server_session_key_proof_hash = client_session.key_proof_hash

# Verify session key proof hash received from server.
assert client_session.verify_proof(server_session_key_proof_hash)

Usage hints

srptools.constants contains basic constants which can be used with SRPContext for server and client to agree upon communication details.
.process() methods of session classes may raise SRPException in certain circumstances. Auth process on such occasions must be stopped.

.private attribute of session classes may be used to restore sessions: .. code-block:: python

  server_private = server_session.private

  # Restore session on new request.
  server_session = SRPServerSession(context, password_verifier, private=server_private)

SRPContext is rather flexible, so you can implement some custom server/client session logic with its help.

Basic values are represented as hex strings but base64 encoded values are also supported:

.. code-block:: python

  server_public = server_session.public_b64

  # Receive server public and salt and process them.
  client_session = SRPClientSession(SRPContext('alice', 'password123', prime=prime, generator=gen))
  client_session.process(server_public, salt, base64=True)

  # Use srptools.hex_from_b64() to represent base64 value as hex.
  server_public_hex = hex_from_b64(server_public)

Links

RFC 2945 - The SRP Authentication and Key Exchange System https://tools.ietf.org/html/rfc2945
RFC 5054 - Using the Secure Remote Password (SRP) Protocol for TLS Authentication https://tools.ietf.org/html/rfc5054

FAQs

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