GPG (GNU Privacy Guard)
Last modified: 2023-06-27
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.txtCrack 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
We can encrypt a message using a PGP public key.
1. Import a Public Key
If we have already a public key, we can import it by the following command.
gpg --import public_key.asc
To list public keys, run the following command.
# -k / --list-keys / --list-signatures
gpg -k
2. Encrypt a Message
If the public key was added, we can encrypt a message using it.
# -e: Encrypt
# -r: Recipient name
gpg -e -r "recipient name" example.txt
# -c: Encrypt only with symmetric cipher
gpg -c example.txt
# --cipher-algo: Encryption type
gpg --cipher-algo AES-256 -c example.txt
After that, hello.txt.gpg will be generated.
Sign
To sign a message with GPG, of course we need to GPG keys.
We can generate a public/secret key by running the command below.
gpg --gen-key
# Output
Real name: test
Email address: test@test.com
To display the contents of the public key, run the following command.
# -a: Ascii armored output
# --export: Export keys
# <key_name>: Optional. If you want to specify the key, specify the name.
gpg -a --export <key_name>
# Output the public key file
gpg -a -o public.key --export
After that, we can sign a message using the public key. At this time, we’re asked for a passphrase, so we need to enter it.
echo 'hello' | gpg --clear-sign
Delete Keys
First off, we can list existing keys as below.
# List public keys
gpg --list-keys
# List secret keys
gpg --list-secret-keys
To delete specific key, run the following commands.
# Delete a public key
gpg --delete-key <key_id>
# e.g.
gpg --delete-key D6BA9423021A0839CCC6F3C8C61D429110B625D4
# Delete a secret key
gpg --delete-secret-key <key_id>
# e.g.
gpg --delete-secret-key D6BA9423021A0839CCC6F3C8C61D429110B625D4