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I want to create a brain wallet using a custom diceware since I don't like the original one. Instead of 7776 words it has 46656 because I use 6 dice for each word instead of 5, and also it only has words with many characters.

So this is what I got so far, please tell me if I made a mistake:

$$\frac{2 ^ {\log_2(46656) · 5} }{ (1 · 10^{15}) · (60 · 60 · 24 · 365)} = 7 \text{ years}$$

  • $2 ^ {\log_2(46656) · 5}$ is the entropy for a password of 5 words
  • $1 · 10^{15}$ is 1 Phash/s, which is the hashing power I'm assuming for this attacker. I don't even know if this makes sense, because an attacker doesn't need to start over for each brain wallet he wants to crack, and also there might have been huge databases of precomputed sha256 hashes before Bitcoin even existed.
  • $60 · 60 · 24 · 365$ represents a year in seconds.
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You calculated the attackers worst case duration ... average case is half of this. – Paŭlo Ebermann Mar 15 '14 at 20:50

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