Rainbow Table
A rainbow table is a precomputed table used to reverse cryptographic hash functions, primarily to crack password hashes stored in databases. Instead of trying every possible password guess in real time (brute force), attackers generate these tables in advance by computing chains of hashes and corresponding plaintexts. This allows them to quickly look up a hash and find its original password more efficiently.
How Rainbow Tables Work
Passwords are usually stored as hashes, which are fixed-length strings generated by a hash function (e.g., MD5, SHA-1) from the original password.
A rainbow table contains chains of alternating plaintext passwords and their hash values. Only the start and end points of these chains are stored, saving space.
When an attacker obtains a hashed password, they try to find it in the rainbow table by applying reduction functions and hashing steps to simulate the chains.
If the hash matches an endpoint in the table, the attacker regenerates the chain from the start to find the exact plaintext password.
Example
Imagine a rainbow table for passwords of length 6 using MD5 hashes. The table might include entries like:
| Start Plaintext | End Hash (Chain Endpoint) |
|---|---|
password |
5f4dcc3b5aa765d61d8327deb882cf99 (MD5) |
123456 |
e10adc3949ba59abbe56e057f20f883e (MD5) |
If an attacker gets a hash 5f4dcc3b5aa765d61d8327deb882cf99 from a stolen database, they look it up in the rainbow table endpoints. Finding it, they regenerate the chain starting from password to confirm the original plaintext.
Important
1: You need to extract the common-hashes.txt.gz file before running the python script.
2: Every hash in the world will not work here as it is not a bruteforce script, it just looks the Rainbow
Table to find a match.