Cryptographic vs. One-Way hash?

[Lazy8s]

I have an assignment where I need to define a cryptographic hash message (whuch I did) but the very next question was to define a one-way hash.....

This really caught me off guard for a minute. I can answer each question easily, but when I saw them right next to eachother it made me start to think...what IS the difference? A cryptographic hash is one way, easy to compute and has no collisions....A one-way hash function is a hash in which the hashed message cannot be derived from the hash value. But they are also supposed to be computationally simple and a good one will be collision free as well!!

Obviously, a OWHF does not HAVE to be collision free but it sure wouldn't have much value if it wasn't.

What is your take?

 

[Zugzwang152]

Umm, no hash function is collision free. By definition, a hashing function will take a variable length input and produce a fixed length output. Because there is an infinte amount of inputs and a finite number of possible outputs, there will always be collisions. However, the likelihood of collisions gets more and more unlikely as the length of the hash output increases.

As for "cryptographic hash message," I've never heard of that term, and apparently neither has Google. Are you sure you're not referring to Message Authentication Code or Keyed-hash Message Authentication Code??

 

[Lazy8s]

http://en.wikipedia.org/wiki/C...ographic_hash_function

First hit on google. The problem is the article is about 40% correct. It looks like the creator just googled "hash function" and tossed in everything they found.