Password Hashing

The data protection code base includes a package Microsoft.AspNetCore.Cryptography.KeyDerivation which contains cryptographic key derivation functions. This package is a standalone component and has no dependencies on the rest of the data protection system. It can be used completely independently. The source exists alongside the data protection code base as a convenience.

The package currently offers a method KeyDerivation.Pbkdf2 which allows hashing a password using the PBKDF2 algorithm. This API is very similar to the .NET Framework's existing Rfc2898DeriveBytes type, but there are three important distinctions:

1. The KeyDerivation.Pbkdf2 method supports consuming multiple PRFs (currently HMACSHA1, HMACSHA256, and HMACSHA512), whereas the Rfc2898DeriveBytes type only supports HMACSHA1.

2. The KeyDerivation.Pbkdf2 method detects the current operating system and attempts to choose the most optimized implementation of the routine, providing much better performance in certain cases. (On Windows 8, it offers around 10x the throughput of Rfc2898DeriveBytes.)

3. The KeyDerivation.Pbkdf2 method requires the caller to specify all parameters (salt, PRF, and iteration count). The Rfc2898DeriveBytes type provides default values for these.

using System;
using System.Security.Cryptography;
using Microsoft.AspNetCore.Cryptography.KeyDerivation;
 
public class Program
{
    public static void Main(string[] args)
    {
        Console.Write("Enter a password: ");
        string password = Console.ReadLine();
 
        // generate a 128-bit salt using a secure PRNG
        byte[] salt = new byte[128 / 8];
        using (var rng = RandomNumberGenerator.Create())
        {
            rng.GetBytes(salt);
        }
        Console.WriteLine($"Salt: {Convert.ToBase64String(salt)}");
 
        // derive a 256-bit subkey (use HMACSHA1 with 10,000 iterations)
        string hashed = Convert.ToBase64String(KeyDerivation.Pbkdf2(
            password: password,
            salt: salt,
            prf: KeyDerivationPrf.HMACSHA1,
            iterationCount: 10000,
            numBytesRequested: 256 / 8));
        Console.WriteLine($"Hashed: {hashed}");
    }
}
 
/*
 * SAMPLE OUTPUT
 *
 * Enter a password: Xtw9NMgx
 * Salt: NZsP6NnmfBuYeJrrAKNuVQ==
 * Hashed: /OOoOer10+tGwTRDTrQSoeCxVTFr6dtYly7d0cPxIak=
 */

See the source code for ASP.NET Core Identity's PasswordHasher type for a real-world use case.