Passwords 101

Jeff Deifik opens with the basics of password storage. He explains how salts stop identical passwords from producing identical hashes, and why unsalted schemes such as Windows LAN Manager and old DES crypt are cheap to attack with precomputed tables. He contrasts these with modern algorithms like bcrypt, whose salts make precomputation impractical.

The core of the talk is a personal project: cracking a dump of 1,576 DES crypt passwords over about five years. He compares John the Ripper and hashcat, noting their different rule syntaxes, and describes how low-quality wordlists had to be cleaned with custom Python utilities alongside sort, uniq and comm. He covers mangling rules, a GPU build chosen for performance per watt, and a group of passwords that used control characters. Those were only found by adding insertion and substitution rules to a large dictionary. The same approach was applied to a leaked set of 1980s BSD Unix password hashes.

He closes with defenses: multi-factor authentication, long random passwords sized to what they protect, and a password manager so every service gets a unique credential, since other services' storage practices cannot be verified. He also suggests undervolting GPUs to cut power use and heat.