This project implements client software for the [OpenPGP card](https://gnupg.org/ftp/specs/OpenPGP-smart-card-application-3.4.1.pdf) standard, in Rust. ## Architecture The project consists of the following crates: - [openpgp-card](https://crates.io/crates/openpgp-card), which offers a relatively low level OpenPGP card client API. It is PGP implementation agnostic. - [openpgp-card-pcsc](https://crates.io/crates/openpgp-card-pcsc), a backend to communicate with smartcards via [pcsc](https://pcsclite.apdu.fr/). - [openpgp-card-scdc](https://crates.io/crates/openpgp-card-scdc), a backend to communicate with smartcards via an [scdaemon](https://www.gnupg.org/documentation/manuals/gnupg/Invoking-SCDAEMON.html#Invoking-SCDAEMON) instance. - [openpgp-card-sequoia](https://crates.io/crates/openpgp-card-sequoia), a higher level API for conveniently using openpgp-card with [Sequoia PGP](https://sequoia-pgp.org/). - [openpgp-card-tests](https://gitlab.com/hkos/openpgp-card/-/tree/main/card-functionality), a testsuite to run OpenPGP card operations on smartcards. ```mermaid graph BT OP["openpgp-card-pcsc
(pcsclite backend)"] --> OC OS["openpgp-card-scdc
(scdaemon backend)"] --> OC["openpgp-card
(low level API)"] OC --> OCS["openpgp-card-sequoia
(high level Sequoia PGP-based API)"] OC -.-> U2[applications using low level API] OCS -.-> U3[Sequoia PGP-based applications] classDef userApp fill:#f8f8f8,stroke-dasharray: 5 5; class U1,U2,U3 userApp; ``` ### The openpgp-card crate Implements the functionality described in the OpenPGP card specification, offering an API at roughly the level of abstraction of that specification, using Rust data structures. (However, this crate may work around some minor quirks of specific card models, in order to offer clients a somewhat uniform view) This crate and its API do not depend or rely on any particular OpenPGP implementation. ### Backends Typically, `openpgp-card` will be used with the `openpgp-card-pcsc` backend, which uses the standard pcsclite library to communicate with cards. However, alternative backends can be used and may be useful. The experimental, alternative `openpgp-card-scdc` backend uses scdaemon from the GnuPG project as a low-level transport layer to interact with OpenPGP cards. Backends implement: 1) functionality to find and connect to a card (these operations may vary significantly between different backends), and 2) a very simple communication primitive, by implementing the `CardClient` trait, to send individual APDU commands and receive responses. All higher level and/or OpenPGP card-specific logic (including command chaining) is handled in the `openpgp-card` layer. ### The **openpgp-card-sequoia** crate Offers a higher level interface, based around Sequoia PGP datastructures. Most client projects will probably want to use only this crate, and ignore the lower level crates as implementation details. ## Testing The subcrate `openpgp-card-tests` (in the directory `card-functionality`) contains the beginnings of a framework that tests the `openpgp-card` library against OpenPGP cards. However, OpenPGP cards are, usually, physical devices that you plug into your computer, e.g. as USB sticks, or Smart cards (this is, of course, the usual point of these cards: they are independent devices, which are only loosely coupled with your regular computing environment. However, for automated testing, such as CI, this can be a complication.) There are at least two approaches for running tests against software-based OpenPGP cards: ### Virtual JavaCards It's possible to run simulated JavaCard applets on a host computer, and make those available via the [PCSC lite](https://pcsclite.apdu.fr/) framework. To simplify testing against such simulated cards, the https://gitlab.com/hkos/openpgp-card-images repository provides Container images for the "SmartPGP" and "YubiKey NEO" OpenPGP card implementations. These images are used to run card-functionality tests on gitlab's CI. See the GitLab CI config [hkos/openpgp-card:.gitlab-ci.yml](https://gitlab.com/hkos/openpgp-card/-/blob/main/.gitlab-ci.yml) and the Dockerfiles and run script: [hkos/openpgp-card:card-functionality/docker/](https://gitlab.com/hkos/openpgp-card/-/tree/main/card-functionality/docker/). ### Emulated Gnuk Gnuk is a free implementation of the OpenPGP card spec by [Gniibe](https://www.gniibe.org/), see: http://www.fsij.org/doc-gnuk/. Gnuk normally runs on STM32-based hardware tokens. However, it's also possible to compile the Gnuk code to run on your host machine. This is useful for testing purposes. Emulated Gnuk is connected to the system via http://usbip.sourceforge.net/. This means that to use an emulated Gnuk, you need to have both root privileges and be able to load a kernel module (so running an emulated Gnuk is not currently possible in GitLab CI). See the [README](https://gitlab.com/hkos/openpgp-card/-/tree/main/card-functionality#running-tests-against-emulated-gnuk-via-pcsc) of the `card-functionality` project for more information on this. ## Acknowledgements This project is based on the [OpenPGP card spec](https://gnupg.org/ftp/specs/OpenPGP-smart-card-application-3.4.1.pdf), version 3.4.1. Other helpful resources included: - The free [Gnuk](https://git.gniibe.org/cgit/gnuk/gnuk.git/) OpenPGP card implementation by [gniibe](https://www.gniibe.org/). - The Rust/Sequoia-based OpenPGP card client code in [kushaldas](https://kushaldas.in/)' project [johnnycanencrypt](https://github.com/kushaldas/johnnycanencrypt/). - The [scdaemon](https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=tree;f=scd;hb=refs/heads/master) client implementation by the [GnuPG](https://gnupg.org/) project. - The [open-keychain](https://github.com/open-keychain/open-keychain) project, which implements an OpenPGP card client for Java/Android. - The Rust/Sequoia-based OpenPGP card client code by [Robin Krahl](https://git.sr.ht/~ireas/sqsc).