commit-reveal.py

import boto3
import codecs
import json
import random

from Crypto.Hash import keccak

# NOTE: `AIRNODE_ID` temporary -- update once Airnode deployed
AIRNODE_ID = '0' * 64

COMMIT_RAW_PATH = "/commit"
REVEAL_RAW_PATH = "/reveal"

s3 = boto3.resource("s3")
bucket = s3.Bucket("commit-reveal-hashes")

def lambda_handler(event, context):

    if event["rawPath"] == COMMIT_RAW_PATH:
        
        # generate random number
        xx = int(random.uniform(1, 1_000_000))
        # convert to hex string
        x = hex(xx)[2:]
        
        # left pad number with 0s in order to make 32 bytes
        padded = "0" * (64 - len(x)) + x
        
        # concatenate number and airnode ID
        concat = padded + AIRNODE_ID
        # generate hash
        keccak_hash = keccak.new(digest_bits=256)
        keccak_hash.update(bytearray.fromhex(concat))
        hsh = keccak_hash.hexdigest()
        
        # save to S3
        s3.Object("commit-reveal-hashes", hsh).put(Body=padded)
        
        return hsh
            
    elif event["rawPath"] == REVEAL_RAW_PATH:
        
        # get hash from request and load corresponding x value
        hsh = event["queryStringParameters"]["hash"]
        obj = s3.Object("commit-reveal-hashes", hsh).get()
        result = obj["Body"].read().decode("utf-8")
        
        # delete (hash, x) pair from storage
        s3.Object("commit-reveal-hashes", hsh).delete()
        
        return result