You can unscramble the hashes of humanity's 5 billion email addresses in ten milliseconds for $0.0069

Not if they don’t want the hash reversed. I.e. keep the salt secret and the hash is still valid for identifying a dataset but functionally only the original vendor could attack the hash via rainbow tables. (It would still be a brute-force attack as per the SO discussion linked above, but they would have the significant advantage of possessing a set of known salts.)

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