He needed computational power similar to that of a mining group to reach his goal. He used the clues that the owner of the wallet revealed to mine 1 BTC.

After announcing the launch of his Juggernaut instant messaging app on the Lightning Network, developer John Cantrell admitted being the one who discovered the key to access the Bitcoin wallet of cryptocurrency entrepreneur Alistair Milne.

Cantrell posted in an article on his Medium blog details of how he succeeding in earning 1 BTC (equivalent to USD 9,400 at the time). He noted that he tried one trillion words to decode the key that allowed him to complete the challenge.

He explained that it was not theft but the evidence that he won a challenge that Milne launched in late May. In his Twitter account, the CEO of Altana Digital Currency Fund invited him to win 1 BTC that he had deposited in his wallet. The award would go to the first person to collect the 12 words of the seed phrase, with which he or she would access the wallet.

To fulfill his promise, Milne periodically revealed a new clue. He had reported that he would launch the last four keywords that would be released simultaneously with the idea of preventing someone from hacking the wallet. However, before posting the eighth word, the businessman realized that his plan had failed, since Cantrell had already guessed the remaining words, found the correct combination, and transferred the funds to his wallet.

Scoping the Problem

Cantrell described in his article that he started preparing just before Milne revealed the eighth clue. He explained that it is necessary to use 2048 words from a fixed list to generate a mnemonic phrase or seed. Without the clues that Milne revealed, the task would have been practically impossible. However, the chances to succeed increased once he knew some of the words that the owner of the wallet posted on his social networks.

Besides, the developer said that knowing eight words, there would be around 1.1 trillion possible mnemonic phrases to verify. He also needed to generate a master private key from the seed and an address from the master private key. However, after several attempts, he realized that the equipment that he was using at the time was not suitable for the task.

The developer said that his laptop could only check about 1,250 mnemonic phrases per second or 108 million phrases per day. Cantrell wrote in his post that it would take his CPU about 25 years to generate and try over a billion possible phrases to open the wallet, with only eight words available.

To accelerate the process, the developer paid about USD 350 for a computational power rental service. However, after checking 85% of the combinations, he was not able to find the correct one. At that moment, he realized that he had to review his method to determine his mistake.

Finding the Solution

A deep review allowed him to verify that the success of the plan that he was implementing depended on the selection of the words in the correct order, which the method that he was using used did not ensure. He even lost hope that it would work and thought about quitting.

Once Cantrell had access to Milne’s wallet, he paid a high fee of 0.01 BTC (equivalent to USD 93) for the mining devices to confirm his transaction faster. He feared that someone else could hack the wallet before him. Later, Milne himself confirmed the withdrawal of 1 BTC from his wallet.

In his article, Cantrell comments that the clues that Milne had revealed m his task, which was still complex. Even Milne invited to read Cantrell’s article, noting: “For those who think that hacking a wallet is easy, read this thread. I knew that every word I revealed made a brute force attack 2048 times easier. ”

Cantrell’s achievement demonstrates that it is necessary to be cautious about the security of wallets and never reveal information about them, especially on social media.

By Willmen Blanco


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