some word list to form a passphrase. The program can be customized to ensure the resulting password complies with the local password policy, say by always producing a mix of letters, numbers and special characters. Such policies typically reduce strength slightly below the formula that follows, because symbols are no longer independently produced. The Password strength of a random password against a particular attack (brute-force search), can be calculated by computing the information entropy of the random process that produced it. If each symbol in the password is produced independently and with uniform probability, the entropy in bits is given by the formula where N is the number of possible symbols and L is the number of symbols in the password. The function log2 is the base-2 logarithm. H is typically measured in bits. {| class="wikitable" |+ Entropy per symbol for different symbol sets ! Symbol set || Symbol count N || Entropy per symbol H'' |- | Arabic numerals (0–9) (e.g. PIN) || 10 || 3.32 bits |- | Hexadecimal numerals (0–9, A–F) (e.g. WEP key) || 16 || 4.00 bits |- | Case insensitive Latin alphabet (a–z or A–Z) || 26 || 4.70 bits |- | Case insensitive alphanumeric (a–z or A–Z, 0–9) || 36 || 5.17 bits |- | Case sensitive Latin alphabet (a–z, A–Z) || 52 || 5.70 bits |- | Case sensitive alphanumeric (a–z, A–Z, 0–9) || 62 || 5.95 bits |- | All ASCII printable characters || 94 || 6.55 bits |- | Diceware word list || 7776 || 12.9 bits |- |} Any password generator is limited by the state space of the pseudo-random number generator used if it is based on one. Thus a password generated using a 32-bit generator is limited to 32 bits entropy, regardless of the number of characters the password contains. Note, however, that a different type of attack might succeed against a password evaluated as 'very strong' by the above calculation. Password generator programs and websites A large number of password generator programs and websites are available on the Internet. Their quality varies and can be hard to assess if there is no clear description of the source of randomness that is used and if source code is not provided to allow claims to be checked. Furthermore, and probably most importantly, transmitting candidate passwords over the Internet raises obvious security concerns, particularly if the connection to the