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Given enough time, hashes are reversible via brute force.

If the attacker steals the entire password table undetected, they have a large amount of time to generate soft collisions. After all they don’t need to hack any particular account, just some 50% of the accounts.

The time can be increased by some coefficient via salting, but the principles remain the same.

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For password hashing, only short-output or broken hash functions have practical collision concerns. The odds of any random collision with a 256-bit hash, and not with a specific hash, is 50% at 2^128 inputs. Salting is a defense against precomputation attacks like rainbow tables and masking password reuse. Attackers crack password dumps by trying known password combinations, previously compromised passwords, brute force up to a certain length, etc. and using the hashing algorithm to compare the output.

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