The Holy Grail

time-consuming. The principle was simple. Passwords, kept in password files with their corresponding user names, were encrypted. It was as impossible to reverse the encryption process as it was to unscramble an omelette. Instead, you needed to recreate the encryption process and compare the results.

There were three basic steps. First, target a computer and get a copy of its password file. Second, take a list of commonly used passwords, such as users' names from the password file or words from a dictionary, and encrypt those into a second list. Third, put the two lists side by side and compare them. When you have a match, you have found the password.

However, there was one important complication: salts. A salt changed the way a password was encrypted, subtly modifying the way the DES encryption algorithm worked. For example, the word 'Underground' encrypts two different ways with two different salts: 'kyvbExMcdAOVM' or 'lhFaTmw4Ddrjw'. The first two characters represent the salt, the others represent the password. The computer chooses a salt randomly when it encrypts a user's password. Only one is used, and there are 4096 different salts. All Unix computers use salts in their password encryption process.

Salts were intended to make password cracking far more difficult, so a hacker couldn't just encrypt a dictionary once and then compare it to every list of encrypted passwords he came across in his hacking intrusions. The 4096 salts mean that a hacker would have to use 4096 different dictionaries - each encrypted with a different salt - to discover any dictionary word passwords.

On any one system penetrated by Electron, there might be only 25 users, and therefore only 25 passwords, most likely using 25 different salts. Since the salt characters were stored immediately before the encrypted password, he could easily see which salt was being used for a particular password. He would therefore only have to encrypt a dictionary 25 different times.

Still, even encrypting a large dictionary 25 times using dif- ferent salts took up too much hard-drive space for a basic