On both hosts:
Install GPG (download from here)
Generate a key pair : gpg –gen-key
List your public keys : gpg –list-keys (optional)
List your secret/private keys : gpg –list-secret-keys (optional)
On the host encrypting (aka the source):
Import your target key (i.e from the host that will decrypt) : gpg –import target.key
Ensure that you have the public key of the target in your trust store : gpg –list-keys
Encrypt your file with the target public key : gpg -e -r target message.txt (or gpg –always-trust -e -r target message.txt if you dont want to be bothered by the public key not being trusted)
note : more details here about user interaction.
On the host decrypting (aka the target):
Export your public key : gpg –export > target.key (to be shared with the source host encrypting)
Decrypt the file with the secret/private key : gpg message.txt.gpg