Re: Why unhashing is not possible?

Barry Margolin wrote:

In article <k1hcj.12858$vd4.5964@pd7urf1no>,
roberson@xxxxxxxxxxxx (Walter Roberson) wrote:

In article <uvgcj.20007$wy2.19474@edtnps90>,
Unruh <unruh-spam@xxxxxxxxxxxxxx> wrote:
"Sebastian G." <seppi@xxxxxxxxx> writes:
Barry Margolin wrote:
How could the hash possibly be guaranteed to be unique?
For a limited set of inputs, this is very easy.
Yes. then it is not a hash. It may be an encryption, or a translation.
http://en.wikipedia.org/wiki/Perfect_hash_function

http://burtleburtle.net/bob/hash/perfect.html
"Minimal perfect hashing"


I've never seen Perfect Hashing referred to as an encryption or
translation, only ever as a "hash function".

These are not the kind of hashing that the OP is talking about. He's asking about cryptographic hashes, which are claimed to be non-reversible.


The OP asked about non-reversible hashes, which are not just the cryptographic hashes.

In this case, an important reason for the non-reversibility is that they're many-to-one.


Which is true for only the set of inputs, not arbitrary subsets of inputs.

The word "hash" is used in a number of different contexts in computer science, you have to be careful not to confuse them.

Nonsense, it's always the same: A hash is a function A^* -> B^m for fixed alphabets A and B and a fixed integer m.
.

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