Breaking the house
How Primedice was exploited for $1M in Bitcoin
This is the story of how we lost around $1 million worth of bitcoin to a hacker who exploited our online casino’s RNG system. This happened last year, but we’ve decided to share our experience for transparency and so that others can learn from our mistakes.
August 2014
Shortly after the launch of the third version of Primedice, our team faced an adversary that challenged the existence of our website. Our team had nearly two years of experience building bitcoin gaming sites, however none of our founders had any coding ability. We were under heavy pressure to avoid further delays and released after a short week of closed beta testing.
The heist began immediately after launch with two unusual players, Nappa & Kane. We noticed unusual betting patterns from both those accounts. Kane was automatically cashed out, we reviewed Nappa’s bets and thought they were highly unusual but could find no wrong-doing and cashed him out after a delay and a brief email exchange
September 2014
After getting spooked by his delayed cashout on Nappa, the exploiter waited a few weeks and created a new account named “Hufflepuff”. Hufflepuff was the largest bettor Primedice had ever seen, he was often seen betting upwards of $8000 worth of bitcoin every second for hours on end. Our entire team was shocked that Hufflepuff continued to beat the house edge (1%) and stack up more and more profit over time.
We were highly skeptical of his winnings and were forced to hold his cashouts time and time again to investigate and each time our developers could not find any wrong-doing. We heavily explored what we thought was every possibility, ran simulations and did the math and came to the conclusion that he was just incredibly lucky.
The Discovery
About two days after sending his final withdrawal placing him above 2037 profit on the Hufflepuff account alone, our main developer detected the exploit after we found a handful of accounts sharing the same server seed.
To understand how Hufflepuff beat our system, one must understand how our provably fair system (RNG) works. A user is shown an encrypted random value (the server seed) before they bet and they must also submit their own random value (the client seed). These two random values are combined and used to determine win or lose. The random encrypted random value used for the bet then is shown to the user after the bet so that they can be guaranteed that their bet is not rigged. You can find the detailed and in-depth explanations of provably fair here:
https://primedice.com/verify and
http://dicesites.com/provably-fairPart of the functionality of our site is that we have to give out decrypted server seeds (to assure users no bet manipulation has occurred) and put a new random seed in place, essentially trashing the old revealed seed. Hufflepuff found a way to “confuse” our server, and made it give out a decrypted server seed that was also an active seed. This was done by sending it more requests than it could handle in a small time period, think hundreds of requests in under a second. The result of this is that he knew all the information required to corroborate the outcomes of his bets. He knew whether if he would win or lose, and could wager accordingly.
We figured this out after frantically checking our servers after a eureka moment. We suspected something could have been going on and eventually realized the possibility of a timing attack described above. Our database had seeds that were both inactive and in use at the same time all connected to Hufflepuff. Along these “Schrödinger” seeds existed many seemingly unused seeds connected to the same accounts, indicative of the rapid fire of requests needed to obtain these.
Déjà vu
Unfortunately we detected this exploit after cashing out Hufflepuff and his handful of accounts 2400+ coins (roughly $1M at the time). Given the nature of Bitcoin there wasn’t much we could do but take it on the chin. We reached out to Hufflepuff via his bitcointalk forum account and demanded the return of the coins, however this backfired unbelievably hard. It turned out that our developer had improperly patched the glitch. In response to our message, Hufflepuff created a new account named Robbinhood and proceeded to rapidly win 2000+ additional bitcoins using a work-around to the patch. He was unable to cashout more than 50 or 60 coins this time around as our site hot-wallet was drained.
Shortly after he privately sent us this message which was preceded with the dox of a primedice employee:
“Your offer is declined. Your demands are laughable. I’m happy to walk away and leave you be, but if you’re going to take this further, then so will I. I don’t think you want this to go further. I actually enjoy this shit. Your move.
Oh, and by the way, there are some pending withdrawals that you need to process.”
And that was the day the house didn’t win…
Evidence for transparency and investigative purposes
Hufflepuff’s deposit address:
https://blockchain.info/address/1BiPXmDrHm7VXZnWy6NnW1ZbPc4dcpfkH5His primary withdrawal address:
https://blockchain.info/address/14iS2UvcLK33xkC1K1qL1dhEbp49aiNfNpEmail:
hufflepuff@anonymousspeech.comRobbinHood withdrawals:
https://blockchain.info/address/14HQ67ZhmATviHi9RdYhbUriAGSFmJpYoB— Note — : Nappa/Kane were two other usernames used early on, amongst many others.
Kane’s Withdrawal address:
https://blockchain.info/address/18dMBap634aESPTeD3FGcAgJ2S9n4qtBTZNappa Deposit address:
https://blockchain.info/address/16h9ggSzUWdvagEJdNvWVYiUkytw6SJgiBNappa email:
kritonian@outlook.comSome IP’s used between accounts: 184.75.221.106, 184.75.223.34 , 151.224.50.156 , 76.179.22.16
Any information that leads to the return of the coins from this incident will be greatly rewarded. We invite you to analyze the above bitcoin addresses and find out where the bulk of the coins ended up if you have the skills.
It’s also important to note that this incident is proof of the strength of our integrity and provably fair system. If at any point we attempted to rig Hufflepuff’s bets (skip nonces etc) we would have instantly realized he was cheating and we would have 2400+ more bitcoins. Hufflepuff only took a brief break from playing after we halved our max bet, I believe he would have cleaned us had we never discovered what was going on.
Sorry for the long read,
Stunna & Primedice
Very interesting. Although it is too bad that more technical details were not revealed, and that it is too bad that he made away with so much money, it is nice to see that at least one bitcoin related casino is operating honestly.
I would be curious to know if such an exploit would have been possible on PD2. If not then do you think it might have been better to have never "upgraded" to PD3, and simply added additional features to PD2?
Although it is really not anyone's business, I am sure that many people are very curious as to what the overall profitability is of both PD overall, and PD3.
One thing that was notably missing from the report was the bitcointalk account names that you are aware of for the people in question. I have noticed that you apparently have not left any negative trust ratings referencing what could be concluded to be this incident (although to be fair, a single negative rating is far from worth a million plus dollars).
I would also be curious to know if you have any leads as to who you think the perpetrator might be or any other related leads regarding him.
