In the world of cybersecurity, one of the techniques attackers use to crack passwords is through rainbow tables.
What Are Rainbow Tables?
Rainbow tables are precomputed tables used to reverse cryptographic hash functions, primarily for cracking password hashes. They allow attackers to look up the hash value and find the corresponding plaintext password quickly, significantly speeding up the cracking process.
How Do Rainbow Tables Work?
Precomputation:
Rainbow tables are generated by hashing a large number of possible passwords and storing these hash values along with their corresponding plaintext passwords in a table. This process is computationally intensive and can take a long time, but it only needs to be done once.
Storage:
These tables can be stored in RAM or as large indexed files on the hard drive. They often take up significant storage space, sometimes multiple terabytes.
Reduction Function:
To reduce the size of the tables, a reduction function is used. This function allows the table to be smaller at the cost of a slightly higher CPU load during the lookup process.
Lookup:
When an attacker gets a hashed password, they use the rainbow table to find the corresponding plaintext password by looking up the hash in the table. If the hash is found, the password is recovered quickly.
Tools for Rainbow Tables
RainbowCrack is one of the prominent tools that provides software for creating and using rainbow tables. It supports several hash algorithms, including LANMAN, NTLM, MD5, and SHA-1. Another popular service is CrackStation, which allows online lookup of hashed passwords against precomputed tables.
Why Are Rainbow Tables Effective?
Rainbow tables are effective against systems that do not use salted hashes. Salting is a technique where a random string (the salt) is added to the password before hashing. This means even identical passwords will produce different hashes if they have different salts, making rainbow tables less effective.
Example of Rainbow Table Attack
Consider an attacker who spends 24 hours generating a rainbow table for an unsalted hashing algorithm, creating a table 1 GB in size. To produce a similar table for a salted algorithm, the attacker would need to account for every possible salt value combined with every possible password, making the table generation process exponentially more difficult and storage-intensive.
For example, a 4-character salt (using a-z, A-Z, 0-9) has 14,776,336 possible combinations. Thus, the attacker would need 14,776,336 times more storage and computational power, making it practically infeasible.
Why Windows Passwords Are Vulnerable
Unfortunately, Windows systems do not support salted hashes for password storage, making them vulnerable to rainbow table attacks. Attackers can obtain password hashes from Windows systems and use tools like RainbowCrack to quickly recover the plaintext passwords.
We will continue the conversation in next blog..................................
Akash Patel
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