GPG (GNU Privacy Guard)

Last modified: 2023-02-15

Cryptography

GPG is a free-software replacement for Symantec's PGP cryptographic software suite.

Decrypt

1. Crack Passphrase from Private Key

gpg2john

First of all, you need to format the private key to make the John to recognize it.

gpg2john private.key > key.txt
gpg2john private_key.asc > key.txt
gpg2john private_key.sig > key.txt

Crack the passphrase using the formatted text.

john --wordlist=wordlist.txt key.txt

custom script

If you cannot crack the passphrase using gpg2john for some reasons (error, etc), you can use the script as alternative.
```
./crackgpg.sh example.gpg passwords.txt
```

2. Import the Private Key

gpg --import private.key
gpg --import private_key.asc
gpg --import private_key.sig

To list the imported keys,

gpg --list-keys
gpg --list-secret-keys

3. Decrypt GPG (PGP) using the Passphrase

At that time, you'll be asked for the passphrase, so enter the passphrase you gotten in the previous section.

# -d: decrypt
gpg -d example.gpg
gpg -d example.pgp

Decrypt ASC File

We can decrypt .asc file by importing private key.

gpg --import private.key
gpg --decrypt example.asc

Encrypt

# -e: encrypt
gpg -e example.txt

# -c: encrypt only with symmetric cipher
gpg -c example.txt

# --cipher-algo: Encryption type
gpg --cipher-algo AES-256 -c example.txt

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