[Kaali]

GPG uses asymmetric keypairs for encryption. You generate (at the same time), two different keys: a private key and a public key. The private key is your identity, which you can use to sign outgoing messages, and decrypt incoming messages. The public key, you share to your associates can be used to verify your signature, or encrypt messages only meant for you.

With asymmetricity, the public key is a key which can only encrypt the message, but even the sender cannot decrypt that same message again with that key. Only the single unshared private key can decrypt them.

This ofcourse means that all parties must have their own key pair, and the public keys have been shared between them. Also they must use a GPG compliant program to encrypt/decrypt or sign and verify the messages.