A rainbow table is a precomputed table for reversing cryptographic hash functions, usually for cracking password hashes. Tables are usually used in recovering the plaintext password, up to a certain length consisting of a limited set of characters. It is a form of time-memory tradeoff, using less CPU at the cost of more storage. Proper key derivation functions employ salt to make this attack infeasible.
Rainbow tables are a refinement of an earlier, simpler algorithm by Martin Hellman that used the inversion of hashes by looking up precomputed hash chains.
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