如何在Go中执行确定性RSA

Question

I have two go services, let's call them A and B. B holds an RSA key pair, while A only knows the public key. I want them to know if they agree on some value V.

I want to do this by having B encrypt encrypt V using the public key and have A do a comparison, but all the crytpo/rsa functions take an RNG which adds entropy and makes each hash of V different. That means I can't compare the hashes.

Is there a function in the go standard library that will deterministicly hash V?

Note: I can achieve this by using a fresh RNG seeded with the same value everytime I hash V, but I want to be able to compute this hash from other languages and that would tie me to Go's RNG.

Answer 1

I want to do this by having B encrypt encrypt V using the public key and have A do a comparison…

You're using the wrong primitive.

If you want the owner of a private key to prove that they have some data, have them Sign that data. The recipient can Verify that signature using the public key.

Use the SignPSS and VerifyPSS methods to do this. The signature will not be deterministic, but it doesn't need to be -- the recipient will still be able to verify it.

Answer 2

Take a look at the docs for EncryptOAEP :

The random parameter is used as a source of entropy to ensure that encrypting the same message twice doesn't result in the same ciphertext.

So the random data does not affect the reader's ability to decrypt the message with only the public key. The cipher text bytes will be different each time you encrypt the same value, which is a good thing.

Take a look at the examples on Encrypt/Decrypt OAEP in those docs. It should be sufficient to get you moving the right direction.