# What is a rainbow table?

> A precomputed lookup structure that reverses unsalted password hashes almost instantly.

Last reviewed: 2026-09-01

## Rainbow table

Category: Attacks

Canonical page: https://moolkey.com/glossary/rainbow-table

A rainbow table is a precomputed structure that maps hashes back to the passwords that produced them, trading storage for speed. Against unsalted hashes it turns cracking into a lookup. Salting defeats it entirely, because every account's hash would need its own table.

### Why they matter less than they used to

Two things reduced their relevance. Salting became standard, which makes precomputation useless. And GPU cracking became so fast that computing hashes on demand is often cheaper than storing and searching terabytes of tables. Rainbow tables remain a good illustration of why salt exists.

### Sources

- [OWASP: Password Storage Cheat Sheet](https://cheatsheetseries.owasp.org/cheatsheets/Password_Storage_Cheat_Sheet.html): Practical guidance for salts, peppers, PBKDF2, Argon2id, and password hashes.
- [CISA: Secure Our World](https://www.cisa.gov/secure-our-world): Public guidance for recognizing phishing and protecting high-value accounts.
- [NIST: Computer Security Resource Center glossary](https://csrc.nist.gov/glossary): Canonical terminology used across US computer security guidance.