Hash and salt passwords in C#

Actually this is kind of strange, with the string conversions – which the membership provider does to put them into config files. Hashes and salts are binary blobs, you don’t need to convert them to strings unless you want to put them into text files.

In my book, Beginning ASP.NET Security, (oh finally, an excuse to pimp the book) I do the following

static byte[] GenerateSaltedHash(byte[] plainText, byte[] salt)
{
  HashAlgorithm algorithm = new SHA256Managed();

  byte[] plainTextWithSaltBytes = 
    new byte[plainText.Length + salt.Length];

  for (int i = 0; i < plainText.Length; i++)
  {
    plainTextWithSaltBytes[i] = plainText[i];
  }
  for (int i = 0; i < salt.Length; i++)
  {
    plainTextWithSaltBytes[plainText.Length + i] = salt[i];
  }

  return algorithm.ComputeHash(plainTextWithSaltBytes);            
}

The salt generation is as the example in the question. You can convert text to byte arrays using Encoding.UTF8.GetBytes(string). If you must convert a hash to its string representation you can use Convert.ToBase64String and Convert.FromBase64String to convert it back.

You should note that you cannot use the equality operator on byte arrays, it checks references and so you should simply loop through both arrays checking each byte thus

public static bool CompareByteArrays(byte[] array1, byte[] array2)
{
  if (array1.Length != array2.Length)
  {
    return false;
  }

  for (int i = 0; i < array1.Length; i++)
  {
    if (array1[i] != array2[i])
    {
      return false;
    }
  }

  return true;
}

Always use a new salt per password. Salts do not have to be kept secret and can be stored alongside the hash itself.