Better error messages if using wrong decryption key

[Juul]

If the public key used for encryption doesn't match the private key you are trying to use for decryption then currently you just get stuff like:

RSA operation error
140024794967576:error:0407206B:rsa routines:RSA_padding_check_SSLv23:block type is not 02:rsa_ssl.c:116:
140024794967576:error:04065072:rsa routines:RSA_EAY_PRIVATE_DECRYPT:padding check failed:rsa_eay.c:602:
Error reading password from BIO
Error getting password