A rainbow table is just a precomputed table of hashes for a lot of passwords. Some tricks are used to make the table smaller, but you can think of it as just a

A rainbow table is just a precomputed table of hashes for a lot of passwords. Some tricks are used to make the table smaller, but you can think of it as just a lookup table. Only the passwords that were precomputed and put into the table will be found. Rainbow tables are usually computed for short passwords (1-10 characters) and limited character set (say, alphanumerics). They are good for finding the bad passwords if you get your hands on a set of MD5 hashed passwords. But they are of no help if you need to reverse a good, long, random password.