Quote from: ribuck on December 09, 2010, 04:46:10 PM

A hash does not need to return a fixed-size bit string (although in software applications it usually does). Show me a definition that says it must be fixed-size. A hash function "number of vowels in the input" is an example of a hash function with no upper size limit. The Wikipedia article says "one can use the datum itself as the hashed value".

You wanted assurance that the balance had not changed "from a reference". Since you can easily calculate the balance of the output of my hash function and compare it to the reference balance, it meets your challenge. :-)

In some cases it might not be fixed size but a hashing function won't ever produce output proportional to the input, that's just a regular function, otherwise, what differentiates a hash from a general function? I was looking at http://en.wikipedia.org/wiki/Cryptographic_hash_function which specifies fixed size but that has other things that aren't strictly necessary like "it is infeasible to find a message that has a given hash" (though that will certainly be true if you can't determine the very large private key used as the input).

"from a reference" meaning, I can verify that the sum of the inputs is the same sum of the inputs of a previous hash (B0 most likely), and such that you can't (easily) create a hash that passes the test even though the sum of the inputs was not the same as the reference (or wasn't derived from a hashed set of inputs at all).