Add Passphrase to Existing SSH Key
1$ openssl rsa -aes256 -in ./id_rsa -out ./id_rsa.hashed
2writing RSA key
3Enter PEM pass phrase:
4Verifying - Enter PEM pass phrase:
You should then use './id_rsa.hashed' as your private key. See https://security.stackexchange.com/questions/59136/can-i-add-a-password-to-an-existing-private-key for details.