Why are slow hash functions used?
The calculation is intentionally slowed down to make it harder for an attacker to brute-force the user passwords in case the password database gets stolen for example. Because a hash function only works “one way”, to get the password for a hash you have to hash random passwords until you find one with a matching hash.
What are hash functions and how to choose a good hash?
Efficiently computable. Should uniformly distribute the keys (Each table position equally likely for each key) For example: For phone numbers, a bad hash function is to take the first three digits. A better function is considered the last three digits. Please note that this may not be the best hash function.
Why are hash values always the same length?
Hash values generated using the SHA256 function are always of the same length, irrespective of the number and type of characters in the input string. The hash value is the result calculated by the hash function and algorithm. Because hash values are unique, like human fingerprints, they are also referred to as ‘ fingerprints ’.
Why should you never use hash functions for message authentication?
The details of the h () depend on the hashing function, but the only thing that concerns us here is that the compression function takes two message blocks and returns another block of the same size. So, first we take IV and M0 and compute h (IV,M0) to get H0. Then we take H0 and M1 and compute H1 = h (H0,M1) and so on down the chain.
Why is the performance of the hash table so slow?
This is also the usual implementation-side choice. But memory addresses are typically equal to zero modulo 16, so at most 1/16 of the buckets will be used, and the performance of the hash table will be 16 times slower than one might expect. When the distribution of keys into buckets is not random, we say that the hash table exhibits clustering.