**scdaemon client for the openpgp-card library** This crate provides `ScdBackend`/`ScdTransaction`, which is an implementation of the `CardBackend`/`CardTransaction` traits that uses an instance of GnuPG's [scdaemon](https://www.gnupg.org/documentation/manuals/gnupg/Invoking-SCDAEMON.html) to access OpenPGP cards. Note that (unlike `openpgp-card-pcsc`), this backend doesn't implement transaction guarantees. **Known limitations** - Uploading RSA 4096 keys via `scdaemon` doesn't work with cards that don't support Command Chaining (e.g. the "Floss Shop OpenPGP Smart Card"). This is caused by a size limitation for client requests via the [Assuan](https://www.gnupg.org/documentation/manuals/assuan/) protocol. Assuan "Client requests" are limited to 1000 chars. Commands are sent as ASCII encoded hex, so APDU commands are limited to around 480 bytes. This is insufficient for importing RSA 4096 keys to the card (all other OpenPGP card operations fit into this constraint). - When using `scdaemon` via pcsc (by configuring `scdaemon` with `disable-ccid`), choosing a specific card of multiple plugged in OpenPGP cards seems to be broken. So you probably want to plug in only one OpenPGP card at a time when using `openpgp-card-scdc` combined with `disable-ccid`. - When using `scdaemon` via its default `ccid` driver, choosing a specific one of multiple plugged in OpenPGP cards seems to only work up to 4 plugged in cards. So you probably want to plug in at most four OpenPGP cards at a time when using `openpgp-card-scdc` with its ccid driver. (This limit has been raised in GnuPG 2.3.x)