mjhjmtu

I'm seeking to cache passphrases for use on an unattended machine. As doing this poses some risk, I'd prefer choosing which passphrases get cached and avoid setting both default-cache-ttl and max-cache-ttl to obnoxiously high values as well as avoid needing to clear gpg-agent's entire cache periodically - hence I'm looking for a solution with gpg-preset-passphrase. Some of the information I found while troubleshooting refer to older versions of GnuPG so I'm unsure if I have sufficiently accounted for all the differences.

First, as prescribed by man 1 gpg-agent, I have export GPG_TTY=$(tty) in my .bashrc.

Now suppose I run eval $(gpg-agent --daemon --allow-preset-passphrase --default-cache-ttl 1 --max-cache-ttl 31536000) to start gpg-agent, noting that gpg-preset-passphrase still honors --max-cache-ttl (default 2 hours).

I then get the keygrip $KEYGRIP of the desired secret subkey with gpg --with-keygrip -K.

With that I try /path/to/gpg-preset-passphrase -c $KEYGRIP. Upon hitting return, this prints:

 gpg-preset-passphrase: caching passphrase failed: Not implemented

Attempting again adding --verbose --debug 6 --log-file /path/to/gpg-agent.log to gpg-agent, my log is appended with

 gpg-agent[4206] listening on socket /run/user/1000/gnupg/S.gpg-agent
 gpg-agent[4207] gpg-agent (GnuPG) 2.1.15 started
 gpg-agent[4207] handler 0x7f86ef783700 for fd 5 started
 gpg-agent[4207] command PRESET_PASSPHRASE failed: Not implemented
 gpg-agent[4207] handler 0x7f86ef783700 for fd 5 terminated

I'm unsure where to proceed from this apart from diving deeper into the source, so I'm wondering if anyone can first correct the steps I'm taking.

I've also got this problem and I've solved by adding configuration to gpg-agent, you can find it in here:

https://stackoverflow.com/questions/49491679/how-to-enter-gnupg-agent-key-passhprase-from-cli