Recently Alistair Milne organized a 1 BTC giveaway of sorts. For those that don't know Alistair Milne, he is a well known investor and entrepreneur. Milne woke up to a news that could easily be life altering and devastating to many. But for him it was his own creation. What makes this not so bad news for Milne is the fact that he himself started revealing his seeds/keys to the public. The intent and purpose off this was to start a giveaway promotion wherein 1 BTC will be given.
But even Alistair didn't account that someone would crack the address this early within 48 hours and that too via brute force method.
Alistair tweeting about the "bad" news.
You can check the original giveaway post here on Alistair's website.
Now lets meet the individual responsible for cracking the address. John Cantrell
It took checking 1 million mnemonics and almost 2 days. As soon as 8 seeds were revealed Cantrell figured out that with 8 seeds revealed he needs to check 240 mnemonics which roughly translates to 1 trillion mnemonics.
He tried testing his programs on his laptop and found that it would take 25 years to create and verify all the mnemonics. So he did what all visionaries do. He innovated and found out a way which was to rent more powerful machines. He turned to cloud computing to aid in his quest to crack the address.
But even with the rented power he still needed approx a 1000x increase in power. He would then turn onto GPU's. Anybody who has been in crypto mining has known how GPU's are used to solve complex problems to mine a block for which they are rewarded in crypto. By his calculations to do this task in 24 hours he needed power equivalent to 80 2080 Ti's worth of power. To my not so well versed in PC terminology users a 2080 Ti is a top end GPU by Nvidia.
Above is an image for the 2080 Ti. One 2080 Ti will cost you 1200 USD and Cantrell needed 80. Cantrell thought of using a sort of GPU pool Vast.ai to rent gpu power from users who were renting it.
At the peak I was testing about 40 billion mnemonics per hour. This means it should have taken around 25 hours to test the 1 trillion mnemonics.
But due to the way Vast.ai works and other issues like latency, unavailability of required GPU's led to almost 2 days in cracking the address. Cantrell started getting restless becasue there was a lot of on the line and lot of assumptions, one of them being what if the seeds revealed were not in their intended order and if that was the case then that would mean another 8! more combinations which he did not account for.
After almost 85% of mnemonics were checked and none of those combinations worked. Cantrell started giving up and came very close to aborting the operation. This was the point that Cantrell almost gave up. But he let it running since he already came so far and VIOLA! exactly at 1 trillion checks and 91% progress, a solution was found.
Finally with his trezor he checked the seeds and saw a balance of 0.99 BTC and with a transfer fee of almost 100 USD transferred the 0.99 BTC to his address.
In the end John Cantrell, due to his quick wit and out of the box approach cracked the address. Now Cantrell has said that he will organize a contest which you cannot win with the help of a software.
This tweet will take you to the article authored by the Cantrell himself which goes in even more details on how 1.1 trillion mnemonics were needed and what software he used.