How We Recovered $300,000 in Bitcoin from an Encrypted Zip File
Cryptanalyst Michael Stay recovers $300,000 in locked Bitcoin keys by executing a sophisticated partial-known-plaintext cryptanalysis attack against legacy Zip encryption.
Summary
The High-Stakes Recovery of Locked Crypto Assets
When a cryptocurrency investor forgot the password to an encrypted Zip archive containing hundreds of thousands of dollars in Bitcoin keys, they turned to legacy cryptanalysis.
Revisiting 20-Year-Old PKZIP Cryptanalysis
Michael Stay revisits Biham and Kocher’s classic known-plaintext attack against PKZIP stream encryption, adapting historical techniques to handle limited known plaintext.
Engineering GPU-Accelerated Key Reduction Engines
Stay outlines the mathematical breakthroughs and custom CUDA GPU kernels developed to reduce the internal CRC32 and linear feedback shift register state spaces.
Successfully Reconstructing the Private Key
Executing the cryptanalytic reduction recovered the internal encryption keys within days, unlocking the archive and securing the Bitcoin funds.
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