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Can you use a keyed hash function as a general purpose hash function?

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I'm working with SWIFFT, a provably secure keyed hash function, which is desirable to me. Unfortunately from what I gather it is ONLY a keyed hash function. Would there be any disadvantages or security problems if I just gave everyone the key and used perhaps public key encryption to do the authentication "manually", using the keyed hash function in a keyless manner as a general purpose hash function?

Steve Mucci avatar
de flag
No no no, SWIFFT, with TWO "F"s. It's a provably secure hash function utilizing Fast Fourier Transform (FFT) as part of its algorithm, hence the "FFT" in "SWIFFT". They proved in SWIFFT that in the worst case scenario you have to solve a lattice problem to find collisions, which is quantum secure cryptography.
kelalaka avatar
in flag
SHA-256, SHA-3, BLAKE2 ( or any cryptographic hash function with at least 256-bit output has secure against quantum attacks)
Maarten Bodewes avatar
in flag
It isn't correct to say that a keyed hash / MAC is *generally* fit to be used as a hash function. If that was the case you could use GMAC as a generic hash algorithm, and you should certainly not do that. So if there is an answer it would be specific to SWIFFT or the family of hashes it belongs to.
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