gpg

Generating a GPG Key Pair

Before you can encrypt or sign anything, you need a key pair: a public key and a private key. The public key can be shared freely; anyone can use it to encrypt a message for you. Your private key, however, must be kept secret; it’s used to decrypt messages and verify signatures.

To generate a key pair, use the following command:

gpg --gen-key

You’ll be prompted to choose a key type (RSA and RSA and Elliptic Curve are popular choices), key size (longer keys are more secure but slower), and provide your name, email address, and a comment (optional). Remember this information, especially your passphrase, as you’ll need it later.

The process might take a few minutes depending on your key size. Once completed, you’ll have a new key pair.

Listing Your GPG Keys

To view your generated keys, use:

gpg --list-keys

This command will show you the details of your keys, including their ID, key type, and expiration date. You’ll see both your public and private keys listed.

Exporting Your Public Key

To share your public key with others, you need to export it. This allows others to encrypt messages that only you can decrypt.

gpg --armor --export <your-email-address> > public_key.asc

Replace <your-email-address> with the email address you associated with your key. The --armor flag ensures the key is in ASCII format, making it easily transferable. The exported key will be saved in public_key.asc.

Encrypting a File

Let’s encrypt a file named my_secret_file.txt using someone else’s public key (e.g., recipient_public_key.asc):

gpg --encrypt --recipient recipient@example.com --output encrypted_file.gpg my_secret_file.txt

Replace recipient@example.com with the recipient’s email address associated with their public key. The encrypted file will be named encrypted_file.gpg.

Decrypting a File

To decrypt the file, use your private key:

gpg --decrypt encrypted_file.gpg > decrypted_file.txt

You’ll be prompted for your passphrase. The decrypted file will be saved as decrypted_file.txt.

Signing a File

GPG can also be used to digitally sign files, ensuring their authenticity and integrity. Signing a file creates a signature that verifies the file hasn’t been tampered with.

gpg --sign my_file.txt

This command will create a signature file (usually with the .sig extension).

Verifying a Signature

To verify a signature:

gpg --verify my_file.txt.sig my_file.txt

This will confirm if the signature is valid and the file hasn’t been altered since it was signed.

Importing a Public Key

To receive encrypted messages, you need to import the sender’s public key:

gpg --import recipient_public_key.asc

Revoking a Key

If your private key is compromised, you must revoke it to prevent unauthorized access. This is a complex procedure and requires careful consideration. Consult the gpg documentation for details on revocation.

This guide provides a solid foundation for using GPG. Remember to always handle your private key with utmost care and practice safe key management. Further exploration of gpg’s options and features will improve your ability to secure your communications and data effectively.