OPAQUE

Introduction

The following software is an PoC implementation of the OPAQUE protocol. This implementation uses ECDH for the OPRF. For more information on the primitives used and the protocol description, see pdf/README.pdf. This PoC is written using SageMath and the pyca/cryptography library.

Description

This software allows a client to register with the server and then to login. The server code is located in server.sage and the client code in client.sage.

OPAQUE-related code is located in files inside the opaque folder. The Sage scripts inside that folder must be compiled into Python files before they can be imported in other Sage scripts. The build-opaque.sh script will do just that. However, for conveniance, compiled files are already commited in this repository.

Pickle

Pickle is used in two places:

1. in the client, for the input of the AuthEnc function and
2. in the server, to serialize the database to a file.

This means that in both cases, we unpickle only data we trust (unless an attacker managed to get access to the server or to the rw key…).

JSON

JSON is used to transmit data between the client and the server, and as mentioned in the Python doc, unlike pickle, deserializing untrusted JSON does not in itself create an arbitrary code execution vulnerability.

Limitations

1. This PoC can register only one user.
2. The H' function is not secure.
3. The sensible cryptographic material is not erase from the memory.
4. When the client quits with an error, the corresponding socket connection on the server must be killed manually (^C).

Execution

cryptography library

As mentioned before, the cryptography library is used, install it with the following command:

sage --pip install cryptography

The server must be launched first, followed by the client with the desired operation (register or login). The client must of course register before he can log in.

sage server.sage
sage client.sage -op register
sage client.sage -op login