[Cryptography] Securing cryptocurrencies
Peter Gutmann
pgut001 at cs.auckland.ac.nz
Fri Mar 13 00:17:26 EDT 2015
Bill Cox <waywardgeek at gmail.com> writes:
>BitCoin has also shown that the typical PBKDF2-SHA256(1000) is essentially
>broken.
>[...]
>These passwords can be brute-force guessed by ASICs in about 2.5 million
>guesses,
Not necessarily:
Mining Bitcoins requires finding a bit string that yields a SHA-256 hash
value beginning with a certain number of zero bits. In other words to mine
a Bitcoin you need to hash data values until you find one whose hash begins
with the required number of zero bits [82][83]. To do that you need a means
of calculating SHA-256 hashes very quickly.
[...]
Passwords and encryption keys are often protected using the same hash
algorithms that the mining ASICs (and FPGAs and GPUs) are designed to
calculate at great speed. By repurposing the hardware that was originally
designed for Bitcoin mining it would be possible to attack hashed passwords
with an efficiency that wasnât feasible before Bitcoin appeared. Having
said that though, the Bitcoin ASICs for which details have been published
are specifically designed for high-speed mining rather than password-
cracking, so that they would require significant changes to their control
circuitry in order to make them suitable for password cracking â itâs not
for nothing that theyâre called application-specific ICs)
Peter.
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