Final answer:
A rainbow table is a precomputed table for reversing cryptographic hash functions to crack password hashes, making attacks feasible by reducing the time required to find a password match.
Step-by-step explanation:
What is a Rainbow Table?
A rainbow table is a precomputed table used for reversing cryptographic hash functions, primarily to crack password hashes. These tables are an instance of time-memory trade-off, applying an efficient use of stored data to save computation time during the attack. A rainbow table consists of chains of potential passwords and their corresponding hash value, allowing an attacker to search for matches of a known hash and find the plaintext password. This is effective only if the hash is not salted, as salting adds a unique value to each password before it is hashed, making the use of a standard rainbow table impractical.
Why do Rainbow Tables Make an Attack Feasible?
Rainbow tables make attacks on password systems feasible because they greatly reduce the time needed to crack a password. Instead of calculating hashes for every possible plaintext password during the attack, an attacker with a rainbow table can simply look up corresponding precomputed hashes. Therefore, it makes cracking processes significantly faster, as long as the password system is not employing preventative measures such as hash salting.