What is "rainbowcrack"

RainbowCrack is a computer program which generates rainbow tables to be used in password cracking. RainbowCrack differs from "conventional" brute force crackers in that it uses large pre-computed tables called rainbow tables to reduce the length of time needed to crack a password drastically. RainbowCrack was developed by Zhu Shuanglei, and implements an improved time-memory trade-off cryptanalysis attack which originated in Philippe Oechslin's Ophcrack.

Some organizations have made RainbowCrack's rainbow tables available free over the internet.