3 ms·

Ideally you'd have something that's hard for the client but easy for the server to verify, though. so maybe prime factoring?

• tshaddox 5y ago
  Or, the server provides a random string of bits with length n and requires a string of bits with length n+m that starts with the provided n bits and whose SHA-1 hash begins with 20 zero bits.
  • wruza 5y ago
    What nonceness!