Question

I’m looking to allow bcrypt support in my authentication library. One of the problems right now is that I assume that the hasher will be of type HashAlgorithm. Bcrypt.net does not implement this class. Also, it’s sealed so I would have to make my own branch off of it and modify it myself. Are there any better alternatives that already implement HashAlgorithm?

Answer 1

Try this:

public class BCryptHasher : HashAlgorithm
{
    private MemoryStream passwordStream = null;

    protected override void HashCore(byte[] array, int ibStart, int cbSize)
    {
        if (passwordStream == null || Salt == null)
            Initialize();

        passwordStream.Write(array, ibStart, cbSize);
    }

    protected override byte[] HashFinal()
    {
        passwordStream.Flush();

        // Get the hash
        return Encoding.UTF8.GetBytes(BCrypt.Net.BCrypt.HashPassword(Encoding.UTF8.GetString(passwordStream.ToArray()), Salt));            
    }

    public override void Initialize()
    {
        passwordStream = new MemoryStream();

        // Set up salt
        if (Salt == null)
        {
            if (WorkFactor == 0)
                Salt = BCrypt.Net.BCrypt.GenerateSalt();
            else
                Salt = BCrypt.Net.BCrypt.GenerateSalt(WorkFactor);
        }
    }

    public int WorkFactor { get; set; }

    public string Salt { get; set; }

    public bool Verify(string plain, string hash)
    {
        return BCrypt.Net.BCrypt.Verify(plain, hash);
    }
}

Usage:

BCryptHasher hasher = new BCryptHasher();
string pw = "abc";
string hash = Encoding.UTF8.GetString(hasher.ComputeHash(Encoding.UTF8.GetBytes(pw)));

Also, I added a helper Verify method so you can verify that the password and hash match, but you can eliminate this if you just call the default BCrypt.Verify.

bool matches = hasher.Verify(pw, hash);

I added some extra properties so you can pass in a pre-computed salt or a work factor to generate a new salt before you do the hash:

string pw = "abc";
hasher.Salt = "$2a$06$If6bvum7DFjUnE9p2uDeDu";
string hash = Encoding.UTF8.GetString(hasher.ComputeHash(Encoding.UTF8.GetBytes(pw)));

I tried it with the BCrypt test case “abc” with a salt of “$2a$06$If6bvum7DFjUnE9p2uDeDu” and got the correct hash.