security - Recommended hash for passwords in ASP Classic

Question

What is the slowest (therefore best) hash algorithm for passwords in ASP Classic?

EDIT: For those unaware, when hashing passwords, slower hashes are preferred to faster to help slow rainbow table style attacks.

EDIT2: And yes, of course speed isn't the only valid concern for hash selection. My question assumes that All other things being equal, the slowest hash method is preferred when hashing a password. Though collision/reverse engineering is of course a concern too, I'm prioritizing speed in this question since it is arguably the most critical factor to consider when comparing popular hash algorithms for use on passwords.

Thanks!

Answer 1

A lot of people seem to be beating on the question-asker because he's looking for a slow hash function. Actually, all other aspects being equal, a slower hash function is more secure than a fast one. This is because a slower hash function results in slower generation of rainbow tables and slower brute forcing or dictionary attacks on the password.

From Thomas Ptacek at http://www.securityfocus.com/blogs/262, as referenced in this Coding Horror article:

The problem is that MD5 is fast. So are its modern competitors, like SHA1 and SHA256. Speed is a design goal of a modern secure hash, because hashes are a building block of almost every cryptosystem, and usually get demand-executed on a per-packet or per-message basis.

Speed is exactly what you don’t want in a password hash function.

Modern password schemes are attacked with incremental password crackers.

Incremental crackers don’t precalculate all possible cracked passwords. They consider each password hash individually, and they feed their dictionary through the password hash function the same way your PHP login page would. Rainbow table crackers like Ophcrack use space to attack passwords; incremental crackers like John the Ripper, Crack, and LC5 work with time: statistics and compute.

The password attack game is scored in time taken to crack password X. With rainbow tables, that time depends on how big your table needs to be and how fast you can search it. With incremental crackers, the time depends on how fast you can make the password hash function run.

The better you can optimize your password hash function, the faster your password hash function gets, the weaker your scheme is. MD5 and SHA1, even conventional block ciphers like DES, are designed to be fast. MD5, SHA1, and DES are weak password hashes. On modern CPUs, raw crypto building blocks like DES and MD5 can be bitsliced, vectorized, and parallelized to make password searches lightning fast. Game-over FPGA implementations cost only hundreds of dollars.

Some comments on the PHP MD5 documentation also discuss preference for slowness.

To answer your question, it looks like BCrypt is the way to go. However, I have not been able to find any implementations for ASP Classic. If that's true, I would stick with a regular hash function like SHA512.