Hybrid encryption with OpenSSL

decrypt.sh

#!/bin/sh

# decrypt the key
openssl rsautl -decrypt -inkey rsa.key -in keyfile_crypted -out keyfile

# use the key to decrypt the data
openssl aes-256-cbc -d -in encrypted.txt -out plain_decrypted.txt -pass file:keyfile

rm keyfile

encrypt.sh

#!/bin/sh

# generate key pair if not exists
if [ ! -e rsa.pub ]; then
	openssl genrsa -out rsa.key 4096
	openssl rsa -in rsa.key -pubout -out rsa.pub
fi

# generate a key for symmetric encryption and encrypt it
openssl rand 32 -out keyfile
openssl rsautl -encrypt -pubin -inkey rsa.pub -in keyfile -out keyfile_crypted

# encrypt the data with the key
openssl aes-256-cbc -e -in plain.txt -out encrypted.txt -pass file:keyfile

# remove the key afterwards
rm keyfile