Secure Password Hashing
I need to store a hash of a single password in a .Net WinForms application.
What's the most secure way to do this?
In particular:
I assume that the algorithm should be either SHA512 or HMACSHA512.
Salt your hash with secure random salt of at least 128bits or longer, to avoid a rainbow attack and use BCrypt, PBKDF2 or scrypt. PBKDF2 comes with NIST approval.
To quote: Archive.org: http://chargen.matasano.com/chargen/2007/9/7/enough-with-the-rainbow-tables-what-you-need-to-know-about-s.html
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.
Fast password validation functions are a problem, cause they can be attacked using brute force. With all the algorithms above you can control the "slowness"
I can recommend BCrypt.net. Very easy to use and you can tune how long it will take to do the hashing, which is awesome!
// Pass a logRounds parameter to GenerateSalt to explicitly specify the
// amount of resources required to check the password. The work factor
// increases exponentially, so each increment is twice as much work. If
// omitted, a default of 10 is used.
string hashed = BCrypt.HashPassword(password, BCrypt.GenerateSalt(12));
// Check the password.
bool matches = BCrypt.CheckPassword(candidate, hashed);
For a server-side implementation with a large number of passwords, you should definitely use a tunable iterated approach like bcrypt. This well-known article on the topic is still (mostly) relevant:
http://www.securityfocus.com/blogs/262
For a single password in a stand-alone application, where the storage location is probably already secured by the system's own authentication system, I think it's much less important. A single strong hash is likely good enough, and adding salt is easy enough that there's no reason not to do so.
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