Re: Probably naive question - SHA1 + MD5 combination

Multiple hash functions isn't a good idea.

What if we can find a set of hash functions that can be proven to be
independent? Can't we combine them to create a stronger hash function?

Simple example: Let's take the four hash functions {HAVAL-160,
RIPEMD-160, SHA-1 and Tiger(2)-160}, and let's assume that they are
independent (it's very likely that they are not!).
All of them take a message as input and produce a 160 bit message
digest as output. The output of the combined hash could be calculated
using XOR: 'C(M) = (H(M) + R(M) + S(M) + T(M)) mod 2^160'.

If the assumption would be true, then isn't breaking this combined hash
as difficult as breaking all of the used hashes separately? Provided
that at least 1 out of those 4 hashes remains invulnerable, the
combined hash should be invulnerable too. Or in other words: an
attacker needs to break all 4 hashes to break the combined hash.

Is this approach correct? If yes, how difficult would it be to prove
independence of hash functions?

Christian

.

Relevant Pages

  • Re: Calculating CRC32 for uploaded files
    ... >> There are other hash functions, but for files of this size you'd be ... crc32 hashes aren't unique while md5 hashes are. ... DeeDee, don't press that button! ...
    (comp.lang.php)
  • hasfunctions need not encrypt their data?
    ... Most papers, as example rfc2246 or papers about HMAC's ... I KNOW this is not a requirement for collision free, ... So why there is no written requirement that "hash functions must ... most widely used Hashes like ...
    (comp.security.misc)
  • Re: Added hashes.
    ... Two hash functions are independent (with respect a ... convincing case that (md4 xor md5) is unbreakable? ... hashes, your definition of independence has to extend to those hashes. ... It can't rely on them being undistinguishable from random oracles. ...
    (sci.crypt)
  • Re: Hash functions strength
    ... Since hash functions are one-way, could, for example, the ... All Hashes are one way in the first sense. ... CRC is one way in the first sense but not in the second. ... ]Typical CRC functions are not one-way. ...
    (sci.crypt)