zkhash Demo

Requirements

1. To run this demo install ZoKrates.

2. To run the on-chain verification, truffle is required. Here is the truffle version information used to test this demo:

   $ truffle version
   
   Truffle v5.4.17 (core: 5.4.17)
   Solidity v0.5.16 (solc-js)
   Node v12.22.1
   Web3.js v1.5.3
   

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Demo Installation

This demo is based on the SHA256 preimage example available here.

However, the code was slightly modified to make it a bit easier to explain. Check the original code under original.zok.

The code we will be working with is under sha256.zok.

To quickly test the demo, run:

git clone https://github.com/kaxxa123/zkhash.git
cd zkhash
./4_all.sh

If everything goes well, you will finally see the verification result from truffle:

Compiling your contracts...
===========================
> Everything is up to date, there is nothing to compile.


Contract: Testing Verifier contract
Verify Result: true
    ✓ Should confirm on Verify (1364ms)


1 passing (1s)

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Demo Details

• To run this demo, we make use of the following online tools:

  SHA256 Online Generator

  Decimal to Hex Convertor

• This ZKP is about proving SHA256 preimage knowledge. In this case our preimage is a 256-bit integer having value 5. More specifically the hash preimage in hex is:

  00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000005
  

• The SHA256 for this hex input is:

  c6481e22c5ff4164af680b8cfaa5e8ed3120eeff89c4f307c4a6faaae059ce10
  

• Next, we need to break this 256-bit output into 2 x 128-bit values and covert them to decimal:

  c6481e22c5ff4164af680b8cfaa5e8ed  -> 263561599766550617289250058199814760685
  3120eeff89c4f307c4a6faaae059ce10  -> 65303172752238645975888084098459749904
  

• In this manner we generate the ZKP proof inputs as shown in 2_prover.sh in the command:

  zokrates compute-witness -a 0 0 0 5 263561599766550617289250058199814760685 65303172752238645975888084098459749904

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