Re: Why unhashing is not possible?

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

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

--
Barry Margolin, barmar@xxxxxxxxxxxx
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
.

Relevant Pages

  • Re: Why unhashing is not possible?
    ... For a limited set of inputs, ... "Minimal perfect hashing" ... only ever as a "hash function". ... asking about cryptographic hashes, ...
    (comp.security.misc)
  • Re: Is there a non-dumb way to replicate "Select distinct" in fortran?
    ... The dumb way is of course to sort on those columns and sequentially ... In that case, you generate an array of hash values, usually a 32 bit ... When the number of distinct keys is modest perfect hashing is well-worth considering, particularly if the universe of distinct keys is known in advance. ...
    (comp.lang.fortran)
  • Re: Why unhashing is not possible?
    ... "Minimal perfect hashing" ... I've never seen Perfect Hashing referred to as an encryption or ... translation, only ever as a "hash function". ...
    (comp.security.misc)