Encrypt and decrypt file with SSH keys

Note that the purpose is to avoid gpg, as possibly not installed.

The Super User answer 576558.

Related to #28.

openssl rsautl -encrypt -pubin -inkey id_ecdsa.pem.pub -ssl -in myMessage.txt -out myEncryptedMessage.txt

Output:

The command rsautl was deprecated in version 3.0. Use 'pkeyutl' instead.
rsautl: Unknown option: -ssl
rsautl: Use -help for summary.

pkeyutl

pkeyutl: command not found

openssl pkeyutl -encrypt -pubin -inkey id_ecdsa.pem.pub -ssl -in myMessage.txt -out myEncryptedMessage.txt

Output:

pkeyutl: Unknown option: -ssl
pkeyutl: Use -help for summary.