What is the shortest hash that can be obtained and why? What happens if you try to achieve a shorter one, is there a fixed limit or does it depend on the length of the hashed data and why?
A:
The shorter your hash, the more likely you are to experience a hash collision.
In practice, a cryptographically strong 32-bit hash is the shortest I would go for most purposes.
Cryptographically strong in this case means that slight changes to the input data will result in drastic changes in the hash value.
Eric J.
2010-06-14 18:31:04
Cryptographically strong 32-bit hashes don't exist, the space is much too small.
starblue
2010-06-14 20:22:24
Whether or not 32 bits is sufficient really depends on the purpose of the hash. Md5 worked very well for many years for a wide variety of purposes. Still, I agree that many more bits are desirable for many applications.
Eric J.
2010-06-14 22:07:36
+1
A:
The length of the hash just has to do with how many unique hashes you need there to be. You can have a one character length hash just as easily as a 100 character one, but there are too many collisions for 1 character.
It just depends on how many unique hashes you need. The formula is (number of characters in hash)^(length of hash). You could have (2)^2 or (68)^2 and have it long enough for what you need.
However, it is different for one-way hashes like md5 instead of encryption ones where you need to translate a given hash into the original string.
Aaron Harun
2010-06-14 18:32:03