Encrypt and decrypt a file

Encryption

sq encrypt takes data from a file or from STDIN and encrypts it, using key material from certificates passed to it.

If you encrypt a file for someone else's User ID and want to be able to read it afterwards, you have to also add your own User ID.

Certificates for encryption - the recipients - can be selected by:

• --for $FINGERPRINT - select the certificate identified by $FINGERPRINT
• --for-email $EMAIL - select all certificates with User IDs containing $EMAIL
• --for-userid $USERID - select all certificates with User ID $USERID
• --for-file $FILE - use the certificates in $FILE
• --for-self - encrypt a message for yourself

One thing to keep in mind: If you use --for-email or --for-userid, sq only considers certificates which are authenticated. If you want to use an unauthenticated certificate, you can use the fingerprint as selector (as fingerprints are self-authenticating) or --for-file.

$ sq encrypt --for-email alice@example.com message.txt --output message.pgp

This encrypts the file message.txt using any certificate containing the email alice@example.com, the result is written to message.pgp. Without --output the encrypted file is printed to STDOUT.

$ sq encrypt --for $FINGERPRINT message.txt --output message.pgp

Does the same, but selects the certificate used for encryption by its fingerprint.

You can create an encrypted file using just a password by providing --with-password - sq will prompt you for the password.

All this can be combined:

$ sq encrypt --for $FINGERPRINT \
    --for-email alice@example.com \
    --for-userid "Bob Example" \
    --with-password \
    message.txt --output message.pgp

The input - the message to encrypt - does not have to be in a file. If the file is missing in parameter list, the message is taken from STDIN.

$ echo "Hello world" | sq encrypt --for $FINGERPRINT
-----BEGIN PGP MESSAGE-----

wV4D+zMBYd4zQtASAQdAM/WW6LvAEEc7SdDEYgo0s38DtywJEB5A8XIt1JhzbTcw
WMqpUI3xbb4ZBqWK9R8/DyIAOqAO1rH55vkdU63OTkj4WKo6f6c8lfMxD8JvYaGV
0j0BMEm+mp706Kpg2Ac/f3Hdn9IHb+jbeCUH/Rem2y+Wr9PrOPyL6vc1MFhCTrd+
9a2XDB3avQcYruJBSxmL
=IX5I
-----END PGP MESSAGE-----

To encrypt a message for yourself, you need to set the recipient(s) in the configuration file beforehand to enable --for-self to apply it:

$ mkdir -p ~/.config/sequoia/sq/
$ sq config template --output ~/.config/sequoia/sq/config.toml
$ $EDITOR ~/.config/sequoia/sq/config.toml
[...]

[encrypt]
for-self = ["1C88780EF239586AF463758094119887B3462B88"]
[...]
[sign]
signer-self = ["1C88780EF239586AF463758094119887B3462B88"]

[...]

$ sq encrypt --for-self --signer-self message.txt

For more information about the configuration file see chapter configuration.

Encrypt and sign

When encrypting a message, adding a signature works as follows:

$ sq encrypt --signer $FINGERPRINT --for-email alice@example.com

or --signer-file $FILE if the signing key is in a file. If there is a signer-self declared in the configuration file, you could also use --signer-self without further information.

Decryption

Decrypting an encrypted file and writing it to a file works as follows:

$ sq decrypt message.pgp --output message.txt

As the encrypted message (usually) contains the ids used during encryption, decryption needs no further help to select the right key. To have sq decrypt sending its output to STDOUT, just leave out the --output parameter.