Using SSH public key to encrypt a file or string

encrypt.txt

# Recently I had to send a password to someone over Skype. Since that's obviously not a good idea, I asked for 
# the person's public SSH RSA key, and used it to encrypt the password itself.


# Convert the public key into PEM format
ssh-keygen -f path/to/id_rsa.pub -e -m pem > ~/id_rsa.pub.pem

# Using the public pem file to encrypt a string
echo "sometext" | openssl rsautl -encrypt -pubin -inkey ~/id_rsa.pub.pem > ~/encrypted.txt

# Or a file
cat ~/some_file.txt | openssl rsautl -encrypt -pubin -inkey ~/id_rsa.pub.pem > ~/encrypted.txt

# To decrypt, you'll need the private key
cat ~/encrypted.txt | openssl rsautl -decrypt -inkey path/to/id_rsa > ~/decrypted.txt