Speaking on Let’s Talk Bitcoin, he described how he “rescued” over 870 BTC (worth $278,000 at today’s prices) from hundreds of vulnerable wallets. He is also the one who salvaged 17 BTC ($5,400) from faulty Counterparty wallets.
In both cases, he detected the “R-value issue.” Wallets were created with recycled “R-values” in formulas that generate random numbers, allowing the private keys to be calculated from the public keys.
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Before malicious hackers were able to exploit the flaw, Jochen preemptively “stole” the contents of these wallets, later returning them to blockchain.info for redistribution.
When stumbling upon Bitcoin in 2013, he first discovered the bug in Android’s random number generator which compromised the security of some Bitcoin wallet apps.
Approaching the issue from a scientific perspective, he was originally not even cognizant of the fact that the wallets were generated by blockchain.info – a response to some detractors who alleged that he was just trying to hack the service to prove its security holes.