.bashrc snippet to automatically start ssh-agent and load it with a key from YubiKey PKCS storage

start_ssh_agent.bashrc

# Tested on Ubuntu 17.10
# Put this into your .bashrc or similar file
# It will ensure each new terminal window has ssh-agent accessible
# and loaded with YubiKey SSH key
# Built upon work from https://stackoverflow.com/a/18915067/401554

SSH_ENV=$HOME/.ssh/environment
PKCS_PATH=/usr/lib/x86_64-linux-gnu/pkcs11/opensc-pkcs11.so

function start_agent {

    # Don't start the agent if YubiKey is not in the reader
    yubico-piv-tool -a version > /dev/null 2>&1 || return 1

    echo -n "Initializing new SSH agent..."
    /usr/bin/ssh-agent | sed 's/^echo/#echo/' > "${SSH_ENV}" || return 1
    echo " [ok]"
    chmod 600 "${SSH_ENV}"
    . "${SSH_ENV}" > /dev/null
    echo "Adding YubiKey to the agent, enter your PIN"
    /usr/bin/ssh-add -t 36000 -s $PKCS_PATH
}

if [ -f "${SSH_ENV}" ]; then
     . "${SSH_ENV}" > /dev/null
     ps -ef | grep ${SSH_AGENT_PID} | grep ssh-agent$ > /dev/null || {
        start_agent;
    }
else
    start_agent;
fi

# Run this command when you have physically removed and re-inserted
# your YubiKey - it will re-add your PKCS key to the agent
alias re-yubi="ssh-add -e $PKCS_PATH && ssh-add -s $PKCS_PATH"