Rfc2898DeriveBytes is very slow in C# .NET Framework (Version 4.8)

Question

I want to hash some passwords in my Project with .NET Framework Version 4.8 using PBKDF2, since it is the only algorithm that is natively implemented. So I coded a class hashing passwords with the recommended iteration count. (In my case SHA256 with 600.000 iterations). Testing the code I noticed that it takes about 1.5 sec to hash a single password, so I tested the code in LINQPad 8 (.NET 8) where the same code runs in 0.5 sec. Out of curiosity I rerun the same Code in LINQPAD 5 (.NET Framework 4.8), where it also took me 1.5 sec. Leaving me with the conclusion that the poor performance stems form the implementation of PBKDF2 in earlier .NET versions. Searching the web has not given me a lot of information, except that there were some performance improvements along the .NET Versions. Am I right with my Conclusion? Is there anything I can do without upgrading the .NET Version or using a 3rd Party package/ AspNetCore.Identity?

LINQPad Code:

byte[] salt = new byte[32]; System.Security.Cryptography.RandomNumberGenerator.Create().GetBytes(salt); var pwhash = new System.Security.Cryptography.Rfc2898DeriveBytes("passwd", salt, 600000, System.Security.Cryptography.HashAlgorithmName.SHA256).GetBytes(32); pwhash.Dump();

I know you're seeing a performance difference but the point of that hash is to be slow - so it's an odd overall complaint to make. — Damien_The_Unbeliever
– Damien_The_Unbeliever, Commented May 7, 2024 at 8:36
Of course it is, but with that poor performance - 1.5 secs instead of 0.5 - I could make only so few iterations, that the security wouldn't be too high before impacting UX. — Graf
– Graf, Commented May 7, 2024 at 8:37
This is one time that "poor performance" is a good thing! If it's only 0.5 seconds in .NET 8 I would be tempted to up the iteration count. This is one part of your application that it pays to pe slow. I think 2 seconds should probably be the target here. How often would a user actually experience this on your site? — phuzi
– phuzi, Commented May 7, 2024 at 9:18
Correct me if I am wrong, but: Hashing Passwords is supposed to secure the passwords in case the database got compromised. So if the attacker has the password hashes he doesn't have to use the slow implementation of PBKDF2 in .NET 4.8 to bruteforce them, but can use faster implementations (e.g. .NET 8). So in that case no, actual poor performance is not good, if it only impacts my hashing speed, but not his. Also >3 seconds log in time in total is not UX friendly I think. — Graf
– Graf, Commented May 7, 2024 at 9:29
I agree that the best fix is not to use an outdated .NET version. But if you have no choice, there are ways to improve performance, see here. On my machine it's roughly: .NET 8 : .NET Framework 4.8 : NET Framework 4.8 unmanaged = 1 : 4 : 2. — Topaco
– Topaco, Commented May 7, 2024 at 10:05

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Rfc2898DeriveBytes is very slow in C# .NET Framework (Version 4.8)

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