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Does anyone know any good hash functions with the following property:

  1. Given buffers buf1 and buf2 of bytes of length n and m with hashes A and B.

  2. Compute in constant time the hash of the concatenation of the data in buf1 and buf2 given n,m,A,B.

In other words, I can piece the hash of the whole thing from its parts without having to reread any parts of the data more than once.

eof
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  • The last property you mention "hash of the whole thing....without having to reread any parts", that sounds like "progressive hashing" or "progressive hash computation" ([some](https://stackoverflow.com/questions/2124468/possible-to-calculate-md5-or-other-hash-with-buffered-reads) [links](https://crypto.stackexchange.com/questions/16510/how-does-progressive-hashing-work)). However, I'm not sure if that's what you're looking for (I've not heard of the first property you mentioned about the hashes of parts being used to calculate final hash...though maybe that is how it works internally). – Anssssss Dec 14 '15 at 21:46

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