[Cryptography] Securing cryptocurrencies

[Peter Gutmann]

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 wasn’t 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 — it’s not
  for nothing that they’re called application-specific ICs)

Peter.