Is there any working zk-snark implementation (even if experimental) among the existing Ethereum clients?

Question

I've asked that question on some places, got a few answers but I'm still missing the bigger piece. I'd like to experiment with zk-snarks. In particular, I'd like to be able to do something similar to this tutorial, i.e., write a program to prove some computation based on a pair of public and secret values, such as:

function senderFunction(x, w) {
  return (
    w.senderBalanceBefore > w.value &&
    sha256(w.value) == x.hashValue &&
    sha256(w.senderBalanceBefore) == x.hashSenderBalanceBefore &&
    sha256(w.senderBalanceBefore - w.value) == x.hashSenderBalanceAfter
  )
}
var proof = zksnarkprove(
    confTxSenderPk,
    senderFunction,
    [hashSenderBalanceBefore, hashSenderBalanceAfter, hashValue],
    [senderBalanceBefore, senderBalanceAfter, hashValue]);

And then be able to verify the correctness of this computation without knowing w from inside an Ethereum contract, for example:

zksnarkverify(
    confTxSenderVk, 
    [hashSenderBalanceBefore, hashSenderBalanceAfter, hashValue],
    zkProofSender)

Is there anything already implemented that allows me to experiment with this usage?

Answer 1

Please find the zksnarks solidity code:

https://gist.github.com/chriseth/f9be9d9391efc5beb9704255a8e2989d

The transaction can be seen on Etherscan and was made on the testnet.

Answer 2

My answer is a fairly dumb one, as I've only had a look around in the code, and I haven't looked into zk-SNARKs properly yet, so apologies in advance if it's no help.

The cpp-ethereum implementation contains the libdevcrypto library, which itself contains LibSnark.cpp. This seems to be built into a separate project with its own cmake file, and there's a set of associated unit test files. There doesn't seem to be anything in any of the other clients (including Parity).

The test file I linked to contains this comment, which would imply something is working at least...

// This verifies a full zkSNARK proof. Let's see if this hocus-pocus actually works...