Encrypt:

gpg -c/--symmetric --cipher-algo AES256 -o/--output file.gpg file.txt
gpg -c/--symmetric -a/--armor --cipher-algo AES256 file.txt

Domyślnie gpg zapisze wynik w pliku file.txt.asc:

cat file.txt.asc
-----BEGIN PGP MESSAGE--slug: gnupg-encryptdecrypt
---

jA0ECQMCsOXaYrOciiL10lwBOJANidEwGbVnS2pArUo2xCtV75Ur1wsLlhkNmGMA
fE+rjySS4POgQAURtFFEf0f74mX2nnscLh14etPmk3Q6TNLoKOJQQyLo6DdTxaZW
PL1XBwVnGnZT9es+cQ==
=voFM
-----END PGP MESSAGE-----

Decrypt:

gpg --decrypt --output file.txt file.gpg

More information

narkive: FORGOT PASSPHASE

Refs