Originally posted by xnor
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A length extension attack is related to using a hash in a MAC. I don't believe it can cause collisions in the hashes. The problem is with authenticated MACs. The answer is to use a well tested, standard algorithm provided by your standard library like an HMAC. The HMAC is available in virtually all standard libraries and very difficult to get wrong. Ironically, if you use BLAKE instead for an authenticated MAC, you should still be using it within HMAC, which means your "extra work" point isn't true.
BLAKE2 is similar in terms of security to SHA3. So if you can use both SHA512 and BLAKE in an HMAC, why do you pick SHA512? Well, you do so to be able to sell your product to anyone. Nobody in the US is buying software outside the mainstream best-vetted cryptography. In many industries they can't for regulatory or certification reasons.
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