Encrypt message with private key

Question

Encrypt message with private key

stephensprinkle-zz opened this issue 11 years ago · comments

Is there a way to encrypt a message with the private key?

Scenario -- The public key of recipients is unknown, but the originator needs to be verified by all recipients via a 'token' of some sort. The message would be decrypted by the peers with the originators public key -- this decrypted token is then verified against a matching plaintext token, thus verifying the identity of the originator.

Thanks!

Rye Terrell · Answer 1 · Thu Oct 03 2013 09:14:01 GMT+0800 (China Standard Time)

This seems a reasonable application. I'll look into this.

Stephen Sprinkle · Answer 2 · Mon Oct 28 2013 12:29:48 GMT+0800 (China Standard Time)

Great! If I develop a method for this I'll be sure to issue a pull request.

Blaine Booher · Answer 3 · Tue Nov 19 2013 05:29:28 GMT+0800 (China Standard Time)

Hi guys! We need this same functionality. Were you able to come up with a solution?

Stephen Sprinkle · Answer 4 · Tue Nov 19 2013 06:15:21 GMT+0800 (China Standard Time)

Not a super elegant solution, but a quick + dirty solution that I've employed thus far is to have a shared private/public key (different than the specific user's private/public keys) that all peers have access to. Any message that ONLY needs verification of origination is encrypted with the shared public key & signed with the individual peer's private key. Included in the encrypted object that is sent is the originating public key.

On the receiving peer's end the message is decrypted with the shared private key and the signature verified and compared against the included public key of the (now decrypted) object to prove origination.

This was the best workaround I've come up with without doing more significant work.

If you're also needing full message encryption, after proof of origination, the receiving peer can pass back their public key via the method above, at which point a fully encrypted (meaning not using a shared private/public key) message between peers can be sent.

Blaine Booher · Answer 5 · Tue Nov 19 2013 08:44:19 GMT+0800 (China Standard Time)

Thanks Stephen. Not ideal, but it's something. Any tips on what other library or mechanism you'd use for just signing with private keys?

Stephen Sprinkle · Answer 6 · Wed Nov 20 2013 02:34:04 GMT+0800 (China Standard Time)

Edit: Actually, give this a look, it might work (I've not used it) -- https://code.google.com/p/jscryptolib/

Honestly, none that I have seen yet for the scenario above in a pure js way.

Blaine Booher · Answer 7 · Wed Nov 20 2013 11:28:37 GMT+0800 (China Standard Time)

Hi guys. We ended up using forge. They have a nice RSA interface that we can just use for signing digests, which is our use case.
https://github.com/digitalbazaar/forge#rsa

Jonas Chevalier · Answer 8 · Sat May 30 2015 03:37:43 GMT+0800 (China Standard Time)

The Forge RSA implementation only allows public key encryption and private key decryption unfortunately.

Eric Wooley · Answer 9 · Sat Nov 04 2017 08:03:10 GMT+0800 (China Standard Time)

It seems to me that the original use case could be solved by having the recipients encrypt and send a random string, and the originator could send back the decrypted value.

Paul Simon · Answer 10 · Tue Apr 03 2018 07:48:50 GMT+0800 (China Standard Time)

@ericwooley made a good suggestion. I tried to take the pubkey generated from cryptico and use that in openssl_public_encrypt() in php, it errs with:
openssl_public_encrypt(): key parameter is not a valid public key

Is there a way to convert the pubkey generated by cryptico to be useable by openssl?