GPG is the fist utilty that most admins think of when they need to encrypt some data at reast. However, it is not very simple to quickly encrypt a file with a password.
OpenSSL makes this much easier.
The following command will encrypt a file:
$ openssl enc -aes-256-cbc -salt -in <FILE> -out <ENCRYPTED-FILE>
enter aes-256-cbc encryption password:
Verifying - enter aes-256-cbc encryption password:
Unencrypt the file with the folloing command:
$ openssl enc -aes-256-cbc -d -in <ENCRYPTED-FILE> -out <FILE>
enter aes-256-cbc decryption password: