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Hash passwords in ASP.NET Core

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This article shows how to call the KeyDerivation.Pbkdf2 method which allows hashing a password using the PBKDF2 algorithm.

Warning

The KeyDerivation.Pbkdf2 API is a low-level cryptographic primitive and is intended to be used to integrate apps into an existing protocol or cryptographic system. KeyDerivation.Pbkdf2 should not be used in new apps which support password based login and need to store hashed passwords in a datastore. New apps should use PasswordHasher. For more information on PasswordHasher, see Exploring the ASP.NET Core Identity PasswordHasher.

The data protection code base includes a NuGet 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 independently. The source exists alongside the data protection code base as a convenience.

Warning

The following code shows how to use KeyDerivation.Pbkdf2 to generate a shared secret key. It should not be used to hash a password for storage in a datastore.

using Microsoft.AspNetCore.Cryptography.KeyDerivation;
using System.Security.Cryptography;

Console.Write("Enter a password: ");
string? password = Console.ReadLine();

// Generate a 128-bit salt using a sequence of
// cryptographically strong random bytes.
byte[] salt = RandomNumberGenerator.GetBytes(128 / 8); // divide by 8 to convert bits to bytes
Console.WriteLine($"Salt: {Convert.ToBase64String(salt)}");

// derive a 256-bit subkey (use HMACSHA256 with 100,000 iterations)
string hashed = Convert.ToBase64String(KeyDerivation.Pbkdf2(
    password: password!,
    salt: salt,
    prf: KeyDerivationPrf.HMACSHA256,
    iterationCount: 100000,
    numBytesRequested: 256 / 8));

Console.WriteLine($"Hashed: {hashed}");

/*
 * SAMPLE OUTPUT
 *
 * Enter a password: Xtw9NMgx
 * Salt: CGYzqeN4plZekNC88Umm1Q==
 * Hashed: Gt9Yc4AiIvmsC1QQbe2RZsCIqvoYlst2xbz0Fs8aHnw=
 */

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 cryptographically strong random sequence of nonzero values
        byte[] salt = new byte[128 / 8];
        using (var rngCsp = new RNGCryptoServiceProvider())
        {
            rngCsp.GetNonZeroBytes(salt);
        }
        Console.WriteLine($"Salt: {Convert.ToBase64String(salt)}");

        // derive a 256-bit subkey (use HMACSHA256 with 100,000 iterations)
        string hashed = Convert.ToBase64String(KeyDerivation.Pbkdf2(
            password: password,
            salt: salt,
            prf: KeyDerivationPrf.HMACSHA256,
            iterationCount: 100000,
            numBytesRequested: 256 / 8));
        Console.WriteLine($"Hashed: {hashed}");
    }
}

/*
 * SAMPLE OUTPUT
 *
 * Enter a password: Xtw9NMgx
 * Salt: CGYzqeN4plZekNC88Umm1Q==
 * Hashed: Gt9Yc4AiIvmsC1QQbe2RZsCIqvoYlst2xbz0Fs8aHnw=
 */

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

Note

Documentation links to .NET reference source usually load the repository's default branch, which represents the current development for the next release of .NET. To select a tag for a specific release, use the Switch branches or tags dropdown list. For more information, see How to select a version tag of ASP.NET Core source code (dotnet/AspNetCore.Docs #26205).