(my personal) yubikey-agent

This is a fork of filippo.io/yubikey-agent, a seamless ssh-agent for YubiKeys.

Key differences in this fork

multi-slot support: Configures all four PIV slots with different PIN and touch policies:
- 9a (PIV Authentication): PIN required once, touch always required
- 9c (Digital Signature): PIN always required, touch always required
- 9d (Key Management): PIN required once, touch never required
- 9e (Card Authentication): PIN never required, touch never required
Command-lines: Uses cobra for a more structured CLI with subcommands

Core features from the original project

Easy to use. A one-command setup, one environment variable, and it just runs in the background.
Indestructible. Tolerates unplugging, sleep, and suspend. Never needs restarting.
Compatible. Provides a public key that works with all services and servers.
Secure. The key is generated on the YubiKey and can't be extracted. Every session requires the PIN, every login requires a touch. Setup takes care of PUK and management key.

Written in pure Go, it's based on github.com/go-piv/piv-go/v2 and golang.org/x/crypto/ssh.

Installation

go install github.com/ncode/yubikey-agent@latest
yubikey-agent setup # generate new keys on the YubiKey

Then add the following line to your ~/.zshrc and restart the shell.

export SSH_AUTH_SOCK="${HOME}/.ssh/yubikey-agent.sock"

Windows

Windows support is currently WIP.

Commands

yubikey-agent list     # List available YubiKey devices
yubikey-agent setup    # Set up a YubiKey with SSH keys\
yubikey-agent unblock  # Unblock pin

Unblocking the PIN with the PUK

If the wrong PIN is entered incorrectly three times in a row, YubiKey Manager can be used to unlock it.

yubikey-agent setup sets the PUK to the same value as the PIN.

yubikey-agent unblock -s <serial>

If the PUK is also entered incorrectly three times, the key is permanently irrecoverable. The YubiKey PIV applet can be reset with yubikey-agent setup --really-delete-all-piv-keys.