Due to the current memory-loss inducing holidays, you may end up forgetting your seldom-used (or recently-changed) login password, SSH or GPG passphrase. If you still have some recollection of what it looked like, one way back in is to generate a wordlist from a regular expression approximation, then feed it to a cracking tool like John the Ripper. Yes, this means cracking your own password.

Let's say your password was the hard for humans to remember Tr0ub4dor+3. But you don't remember the various capitalizations, which letter did you l33t, which punctuation mark and suffix you used in a feeble attempt to slow down a potential attacker. You can generate a plausible wordlist using regdlg, the regular expression grammar language dictionary generator

regldg -m 15 -us 255 '[tT]r[0o]ub[@a]d[0o]r.[0-9]!?' >/tmp/mywl.txt

Here -m 15 sets the maximum length, while -us 255 enables the regexp period to match all alphanumeric characters plus punctuation and symbols (the regexp universe). Then, download and install a “jumbo”-patched John the Ripper:

git clone https://github.com/magnumripper/JohnTheRipper
cd JohnTheRipper/src
make linux-x86-native
cd ../run

Now generate a password file using unshadow, ssh2john or gpg2john (you may want to delete irrelevant lines from the output)

./gpg2john ~/.gnupg/secring.gpg >/tmp/gpwd.txt

and crack the password:

./john --show --wordlist=/tmp/mywl.txt /tmp/gpwd.txt

There's usually no point in enabling the --rules john option (or writing custom John rules) as they don't deal with the kind of variation pertinent to approximate password recall.

Tips

• Be sure to delete your cracking script (if you saved the above commands to one) and your .bash_history, or better yet change your passphrase after recovering it.
• Of course, there's also the BOFH method of recalling passwords by recreating the scenario which made you dream them up in the first place, but it may not always applicable (or definitive in recovering all details).