Introducing the petlib library

One of my key annoyances while doing work in privacy technologies is the poor support of key cryptography libraries in my favorite Python programming language. Today, I would like to share my work on building petlib, a more or less pythonic, wrapper around the OpenSSL low level crypto and math libraries, as well as numerous example privacy technologies (PETs) that I have implemented as examples.

The needs of someone doing research in the PETs field are quite different from other developers: on one hand we need access to low level primitives (such as block cipher and hash function operations), as well as low level mathematical functions on big integers and elliptic curves on finite fields. A number of available libraries try to hide those primitives from developers behind abstractions such as “signed envelopes” or “secure sockets” — which so not serve those who try to build different abstractions. On the other hand, issues such a tight memory management and absolute control over other low-level aspects of the library are not essential; in fact a clean programming interface that leads to beautifully clear reference code for proposed protocols is preferable.

The petlib library is available for everyone to use, and after installing the OpenSSL prerequisites can be acquired through the python repositories through:

pip install petlib

The petlib library was used as the basis for teaching the labs of the Privacy Enhancing Technologies course at UCL, and thus has extensive documentations, and is properly version controlled, packaged and tested:

• petlib github repository
• petlib installation and programming documentation (read the docs)
• petlib listing on pypi

The best way to get a feel for how the library can be used to build PETs prototypes is to browse the examples in the source tree:

• A toy RSA example
• A simple Schnorr Zero-Knowledge Proof
• An additivelly homomorphic public key encryption scheme
• A generic engine for building zero-knowledge proofs using sigma protocols
• The Groth-Kohlweiss ring signature and zero-cash scheme
• The algebraic MAC scheme by Chase, Meiklejohn and Zaverucha
• An anonymous credential scheme based on the aMAC scheme above
• The Baldimtsi and Lysyanskaya anonymous credentials light scheme

In terms of more real-work research project, we have already used petlib for implementing prototypes for a few projects and labs:

• The centrally banked cryptocurrency framework (with Sarah Meiklejohn)
• A private stats collection system for Tor (with Melis and De Cristofaro)
• Exercises in Privacy Enhancing Technologies (for UCL COMPGA17)

One key missing component from the underlying OpenSSL crypto library is support for computations on pairings of elliptic curves. This limits the types of protocols that can currently be implemented with petlib, until such functionality becomes available in the underlying libraries (please contribute!) Bug reports and pull requests with fixes to the code and documentation are very welcome.