Asymmetric encryption
For Asymmetric encryption you must first generate your private key and extract the public key.
openssl genrsa -aes256 -out private.key 8912
openssl rsa -in private.key -pubout -out public.key
To encrypt:
openssl rsautl -encrypt -pubin -inkey public.key -in plaintext.txt -out encrypted.txt
To decrypt:
openssl rsautl -decrypt -inkey private.key -in encrypted.txt -out plaintext.txt