If someone knows that I am using Diceware, can they just use the word list to search for my passphrase?
The Diceware method is secure even if an attacker knows that you used Diceware to pick your passphrase, knows how many words are in your passphrase and knows the word list you used. The security of Diceware comes from the huge number of combinations that an attacker must search through even with that knowledge . The Diceware word list contains 7776 words, so if you pick a five-word passphrase, there are 7776 x 7776 x 7776 x 7776 x 7776 combinations. That is over 2**64 (2 to the 64 power or 2.6 X 10**19) possibilities. A six word Diceware passphrase confronts an attacker with 2**77 (2 X 10**23) combinations; seven words 2**90 (1.5 X 10**27).
