The cryptographer told how he helped the unlucky …

The cryptographer told how he helped the unlucky …

The cryptographer tells how he helped an unlucky investor recover $ 300,000 of bitcoins

Cryptographer, Ph.D. and former Google engineer Mike Stay in his blog talked about an unusual order to restore access to a bitcoin wallet, which he received from a “Russian guy”.

The customer contacted Stay on LinkedIn after discovering his work, written 19 years ago, and gave him an almost impossible task – to crack an encrypted Zip file with private keys from a bitcoin wallet. Bitcoins for $ 10,000 – 15,000 were bought in 2016, but over the years their value has exceeded $ 300,000.

“He put private keys in an encrypted Zip file and couldn’t remember the password,” says Stay.

The main problem was that the encrypted file contained an almost unlimited number of combinations, only one of which was correct. Initially, Stay estimated the life of work at one year, and the costs, according to his forecasts, were in the region of $ 100,000, and this is subject to the presence of a large GPU farm..

“He amazed me by saying that he was ready to go for it in order to recover the key,” writes the author.

He described a similar attack in the same publication many years ago, but in his example the search for a solution required enumerating only a few options, while in this case it was necessary to check “trillions of keys”. “If I had to conduct 2 to 32 degrees of tests for each of them, it would take several hundred thousand years to solve the problem,” he adds..

Stey developed several complex algorithms that significantly reduced the number of possible options, but this did not bring the desired result either.

The cryptographer told how he helped the unlucky ...

“Luckily, he still had that laptop and knew the exact date when the file was encrypted. Since the grain of InfoZip is an unpredictable timestamped value, this information promised to significantly reduce the work – “just” to 10 quintillion – and make it doable within a couple of months on an average GPU farm. We made an agreement and I got to work. “.

The cryptographer notes that he had to re-learn the skills he possessed while writing the original work. In practice, cracking the file took only a few days.

It is important to add that he did not crack the bitcoin keys themselves or interfere with the cryptocurrency protocol. The task was reduced only to breaking the file containing the necessary information.

The cryptographer told how he helped the unlucky ...

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