There are plenty of command line encryption tools for Linux and Unix computers.
There's GPG, for example, which can do both symmetric and public-key encryption.
→ Symmetric encryption is where the same key, or password, locks and unlocks a file. Public-key encryption is where you have two keys, one to lock data and the other to unlock it. You can publish the locking key openly - indeed, it's called the public key - so anyone can send you files securely, but you keep the unlocking key private, so that only you can read them back later on.
Then there's the OpenSSL toolkit, which you can use in two ways: built in to your own software to give it encryption features, or as a command line tool for all sorts of encryption-related tasks.
And now, reports SophosLabs, there's Linux/Ransm-C.
If you think that sounds like a very curious and malware-like name for an encryption toolkit, you'd be right.
