openpgp-card/README.md

OpenPGP card client library

This project implements a client library for the OpenPGP card specification, in Rust.

The project consists of a number of crates:

• openpgp-card, which offers an implementation-agnostic, relatively low level OpenPGP card client API. It is PGP implementation agnostic.
• openpgp-card-sequoia, a higher level API for conveniently using openpgp-card with Sequoia PGP.
• openpgp-card-pcsc, a backend to communicate with smartcards via pcsc.
• openpgp-card-scdc, a backend to communicate with smartcards via an scdaemon instance.
• openpgp-card-tests, a testsuite to run OpenPGP card operations on smartcards.

Architecture

graph BT
    OP["openpgp-card-pcsc <br/> (pcsclite backend)"] --> OC
    OS["openpgp-card-scdc <br/> (scdaemon backend)"] --> OC["openpgp-card <br/> (low level API)"]
    OC --> OCS["openpgp-card-sequoia <br/> (high level, sequoia based API)"]
    OC -.-> U1[non-sequoia/low level user application]
    OCS -.-> U2[sequoia-based user application]

classDef userApp stroke-dasharray: 5 5;
class U1,U2 userApp;

The backends implement very simple transport functionality. They can send APDU commands and receive responses. All OpenPGP card-specific logic, as well as command chaining are handled in openpgp-card.

Acknowledgements

This project is based on the OpenPGP Card spec, version 3.4.1.

Other helpful resources included:

• The free Gnuk OpenPGP card implementation by gniibe.
• The Rust/Sequoia-based OpenPGP card client code in kushaldas' project johnnycanencrypt.
• The scdaemon client implementation by the GnuPG project.
• The open-keychain project, which implements an OpenPGP card client for Java/Android.
• The Rust/Sequoia-based OpenPGP card client code by Robin Krahl.