Weaknesses in SHA-1

[Atom 'Smasher']

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with all this talk of (allegedly!) weak and broken hashes, i'd like to 
throw out a construct to combine 2 or more hashes and (it seems) make the 
construct more secure than either one of the hashes independently: take 
two or more hashes and XOR them.

if i XOR the output of an SHA-1 and RIPEMD-160 hash, the only way to 
"break" the resulting hash would require breaking *both* SHA-1 and 
RIPEMD-160.

the same mechanism can apply to more than two hashes as input, but i'm not 
enough of a math guy to figure out where is the point of diminishing 
return (or if there is such a point). intuitively, it seems (to me) that 
if N hashes are used as input, the protocol is secure as long as any one 
of the input hashes can not be broken. i'm also not enough of a math guy 
to figure out (quantifiably) what would be gained (or lost) by combining 
hashes of different sizes, and maybe even truncating the output.

and no, the little voices in my head are not suggesting that this ~should~ 
be done because the sky is falling... they're just saying that this 
~could~ be done, if the general consensus is that the sky will fall. OTOH, 
what if some secret agency known by three letters could break some hashes, 
but not others....


          ...atom

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