I confess that I had to look up "key stretching". Is it usual to do this, and why do you do it?
[0] http://crackstation.net/hashing-security.htm
"Salt ensures that attackers can't use specialized attacks like lookup tables and rainbow tables to crack large collections of hashes quickly, but it doesn't prevent them from running dictionary or brute-force attacks on each hash individually. High-end graphics cards (GPUs) and custom hardware can compute billions of hashes per second, so these attacks are still very effective. To make these attacks less effective, we can use a technique known as key stretching. The idea is to make the hash function very slow, so that even with a fast GPU or custom hardware, dictionary and brute-force attacks are too slow to be worthwhile. The goal is to make the hash function slow enough to impede attacks, but still fast enough to not cause a noticeable delay for the user."
I intentionally gave you some good options (PBKDF2, bcrypt) and some really bad ones (MD5, in house) to chose from. I assume that you are using a tested and trusted library to implement PBKDF2?
But isn't the work factor - the "number or iterations" in PBKDF2 is doing the same thing as key stretching, i.e. "make the hash function very slow". There is also a similar parameter in bcrypt. So you don't need to add anything else special to the crypto, and indeed shouldn't.
I'd makes bruto forcing harder - longer :-)
My i ask, what do you use asp.net mvc for?
Myself (@Belgium):
ASP.Net MVC mostly for: - Ecommerce - Invoicing application (SMB development) - DDD application