public static byte[] GenerateSalt()
{
    var data = new byte[64];
    var rng = new RNGCryptoServiceProvider();

    rng.GetBytes(data);

    return data;
}

public static byte[] ComputeHash(string password, byte[] salt)
{
    var salted = salt.Concat(Encoding.Default.GetBytes(password));
    using (var sha512 = SHA512.Create())
    {
        return sha512.ComputeHash(salted.ToArray());
    }
}

#region IUserRepository Members

public bool ValidateUser(User user)
{
    var userGet = context.Users.FirstOrDefault(x => x.Username == user.Username);
    if (userGet == null)
        return false;

    var hashedSalt = Convert.FromBase64String(userGet.PasswordSalt);
    var hashedPassword = Convert.ToBase64String(ComputeHash(user.PasswordHash, hashedSalt));

    if (userGet.PasswordHash.Equals(hashedPassword))
        return true;

    return false;
}

#endregion