Having issues Decrypting Binary File

[andrewlaguna824]

Hello!

I have an encrypted, signed file that is in binary format. My goal is to decrypt the message and verify its signature.

Currently, I am using helper.DecryptVerifyMessageArmored(senderPublicKey, receiverPrivateKey, nil, cipherText).

The cipher text is in binary format (e.g. ��Կ�ú�K斖��1wPb"�jItc~��` ... ).

When calling the above decryption function, I receive the error:

 gopenpgp: unable to unarmor ciphertext: gopenpgp: error in unarmoring message: gopenpgp: unable to unarmor: EOF

After some digging around online, it seems that perhaps the issue is that the cipher text is unarmored (link).

If this is the issue, is there a way I need to armor the cipher text before passing to the decrypt function? I do not have the ability to change the incoming file -- it is being received from a third party.

As a note, I can successfully decrypt and verify the message using the gpg command line util.

[marinthiercelin]

Hi, there's no helper function to decrypt unarmored messages.

But you can write your own using the crypto package.

The code would look something like that:

func DecryptMessageUnarmored(
	privateKey string, passphrase []byte, ciphertext []byte,
) (plaintext string, err error) {
	var privateKeyObj, unlockedKeyObj *crypto.Key
	var privateKeyRing *crypto.KeyRing
	var pgpMessage *crypto.PGPMessage
	var message *crypto.PlainMessage

	if privateKeyObj, err = crypto.NewKeyFromArmored(privateKey); err != nil {
		return "", errors.Wrap(err, "gopenpgp: unable to unarmor private key")
	}

	if unlockedKeyObj, err = privateKeyObj.Unlock(passphrase); err != nil {
		return "", errors.Wrap(err, "gopenpgp: unable to unlock private key")
	}
	defer unlockedKeyObj.ClearPrivateParams()

	if privateKeyRing, err = crypto.NewKeyRing(unlockedKeyObj); err != nil {
		return "", errors.Wrap(err, "gopenpgp: unable to create new keyring")
	}

	if pgpMessage, err = crypto.NewPGPMessage(ciphertext); err != nil {
		return "", errors.Wrap(err, "gopenpgp: unable to unarmor ciphertext")
	}

	if message, err = privateKeyRing.Decrypt(pgpMessage, nil, 0); err != nil {
		return "", errors.Wrap(err, "gopenpgp: unable to decrypt message")
	}

	return message.GetString(), nil
}

This is basically the same helper, but the message object is built with crypto.NewPGPMessage instead of crypto.NewPGPMessageFromArmored

[andrewlaguna824]

Thank you for the quick response! I received the below error now:
gopenpgp: error in reading message: openpgp: unsupported feature: Symmetrically encrypted packets without MDC are not supported

1. it looks like the sender is providing an encrypted packet with an old encryption algorithm
2. It seems odd that the error is stating this is a symmetrically encrypted packets, even though we're using asymmetric keys.

For 1. it looks like I may need to use the crypto library to get access to the Config that has InsecureAllowUnauthenticatedMessages as it doesn't look like this fork includes that. Would that be your suggestion?

[twiss]

OpenPGP messages always use symmetric encryption, (usually) in combination with asymmetric encryption.

This library is not a fork of go-crypto, it's a high-level wrapper, and as such doesn't provide support for the low-level config options, indeed. So I would suggest using go-crypto directly, in this case.

[andrewlaguna824]

Thank you for the response! I appreciate you and @marinthiercelin answering my questions.