File encryption and decryption with gpg

note.md

• Let's make sure we use the most recent version of gpg

$▶ gpg --version
gpg (GnuPG) 2.2.12
libgcrypt 1.8.4
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Home: ...
Supported algorithms:
Pubkey: RSA, ELG, DSA, ECDH, ECDSA, EDDSA
Cipher: IDEA, 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH,
        CAMELLIA128, CAMELLIA192, CAMELLIA256
Hash: SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
Compression: Uncompressed, ZIP, ZLIB, BZIP2

• We have this secret file, test.txt, with a secret message. We want to encrypt this file.

$▶ echo 'hello world' > test.txt
$▶ cat test.txt
hello world

• We will encrypt this file with AES256 and a passphase. When asked for a passphase, enter a long enough one, and verify it again.

$▶ gpg --cipher-algo AES256 -c test.txt

• A new file, test.txt.gpg, is created. We can now remove the original test.txt file.

• Note that gpg-agent caches this passphase. We should clear the passphase from cache.

$▶ echo RELOADAGENT | gpg-connect-agent
OK

• We can decrypt the file using the same passphase.

$▶ gpg test.txt.gpg
gpg: WARNING: no command supplied.  Trying to guess what you mean ...
gpg: AES256 encrypted data
tgpg: encrypted with 1 passphrase

• After decrypting, we can clear the passphase from cache again.

$▶ echo RELOADAGENT | gpg-connect-agent
OK