This is a python script to verify rolls on just-dice.com

jd-verify.py

#!/usr/bin/env python
import hmac
import hashlib
from sys import argv, exit, stderr

def hmac_sha512(key, message):
    return hmac.new(key, message, hashlib.sha512).hexdigest()

def roll(server_seed, client_seed, nonce):
    # Generate key and message strings.
    key = '%s:%s:%s' % (nonce, server_seed, nonce)
    message = '%s:%s:%s' % (nonce, client_seed, nonce)

    # Generate hmac-sha512 hash.
    hexdigest = hmac_sha512(key, message)

    # Convert hexdigest into "lucky" number.
    for i in xrange(25):
        lucky = int(hexdigest[5*i:5*i+5], 16)
        if lucky < 1000000:
            return lucky/10000.0

    # If none of the 25 blocks were suitable, use the last 3 characters.
    lucky = int(hexdigest[-3:], 16)
    return lucky/10000.0

def verify_server_seed(server_seed, server_seed_hash):
    return hashlib.sha256(server_seed).hexdigest() == server_seed_hash

def usage():
    msg = 'usage: server_hash server_seed client_seed start_nonce [end_nonce]\n'
    stderr.write(msg)
    exit(1)

def main():
    if len(argv) < 5:
        stderr.write('too few arguments\n')
        usage()

    server_hash = argv[1]
    server_seed = argv[2]
    client_seed = argv[3]
    start_nonce = argv[4]
    if len(argv) > 5:
        end_nonce = argv[5]
    else:
        end_nonce = start_nonce

    if verify_server_seed(server_seed, server_hash):
        print 'server seed matches hash'
    else:
        print 'server seed does not match hash!'
        exit(0)

    print '%5s: %8s' % ('nonce', 'lucky')
    for nonce in xrange(int(start_nonce), int(end_nonce)+1):
        print '%5s: %8.4f' %(nonce, roll(server_seed, client_seed, nonce))

if __name__ == '__main__':
    main()