get_hash_locally.zok

import "hashes/sha256/512bitPacked" as sha256packed

/*
*   c0 - First part of the hash c_k_i (collision key)
*   c1 - Second part of the collision key
*   k - lenght of the hash chain
*   blockNumber - The redactable-blockchain block number
*/


def main(field c0, field k, field blockNumber) -> (field[4][2]):

    field[2] hash_result = [0, 0]
    field[4][2] h = [hash_result; 4]

    
    //c1 = SHA(c0 || blockNumber) 
    field[2] tmp = sha256packed([0, 0, blockNumber, c0])
    
    h[0] = tmp
    
    
    for field i in 1..3 do
        field h0 = h[i-1][0]
        field h1 = h[i-1][1]
        
        
        tmp = sha256packed([0, blockNumber, h0, h1])
        
        h[i] = tmp

    endfor
    

   return h