Which password-cracking technique relies on precomputed hashes to speed up cracking attempts?

Which password-cracking technique relies on precomputed hashes to speed up cracking attempts?

• A. Brute force
• B. Rainbow tables
• C. Dictionary attack
• D. Phishing

Answer: (A)

Rainbow tables rely on precomputed hash values to speed up password cracking. Instead of hashing each guess as the attack runs, an attacker precomputes a vast collection of candidate passwords and their corresponding hashes, then stores them for quick lookup. When trying to crack a password, the attacker can simply search the table for the target hash to retrieve the likely plaintext password. To keep the table practical in size, rainbow tables use chain reductions: a hash is converted back to another candidate password, which is hashed again, and the process repeats, with only the start and end of each chain stored. This approach dramatically reduces real-time computation at the cost of large precomputation and storage, and it hinges on the absence of salting. If the target system uses unique salts (and strong hashing), the precomputed tables become ineffective because the same password will hash differently per user. In contrast, brute force exhausts all possibilities without precomputation, dictionary attacks use a predefined list of common passwords, and phishing is a social-engineering method rather than a hashing-based cracking technique.

Rainbow tables rely on precomputed hash values to speed up password cracking. Instead of hashing each guess as the attack runs, an attacker precomputes a vast collection of candidate passwords and their corresponding hashes, then stores them for quick lookup. When trying to crack a password, the attacker can simply search the table for the target hash to retrieve the likely plaintext password. To keep the table practical in size, rainbow tables use chain reductions: a hash is converted back to another candidate password, which is hashed again, and the process repeats, with only the start and end of each chain stored. This approach dramatically reduces real-time computation at the cost of large precomputation and storage, and it hinges on the absence of salting. If the target system uses unique salts (and strong hashing), the precomputed tables become ineffective because the same password will hash differently per user. In contrast, brute force exhausts all possibilities without precomputation, dictionary attacks use a predefined list of common passwords, and phishing is a social-engineering method rather than a hashing-based cracking technique.