For symmetric encryption

• To encrypt:

 openssl aes-256-cbc -salt -a -e -in plaintext.txt -out encrypted.txt

• To decrypt:

 openssl aes-256-cbc -salt -a -d -in encrypted.txt -out plaintext.txt

For Asymmetric encryption

 openssl genrsa -des3 -out private.key 4096
 openssl -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