example.cs

// User entity:
class User {
    // ...
    public Password Password { get; set; }
}

// register new user:
var user = new User();
user.Password = new Password(formPassword);

// verify user's password
var user = Db.FindUserByUsername(formUsername);
if (user != null && user.Password.VerifyPassword(formPassword))
{
    return user;
}
return null;

Password.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace Domain.ValueObjects
{
    /// <summary>
    /// Password stored as salted hash
    /// </summary>
    public class Password
    {
        /// <summary>
        /// Encoding used to convert string password to sequence of bytes to hash
        /// </summary>
        private static readonly Encoding _encoding = Encoding.UTF8;

        #region Data

        public byte[] Hash { get; set; }

        public byte[] Salt { get; set; }

        #endregion

        #region Constants

        /// <summary>
        /// Length of salt in bytes
        /// </summary>
        public const int SaltLength = 64;

        /// <summary>
        /// Length of hash in bytes
        /// </summary>
        public const int HashLength = 64;

        #endregion

        #region Constructors

        public Password(byte[] hash, byte[] salt)
        {
            Hash = hash;
            Salt = salt;
        }

        public Password(string password)
        {
            Salt = GenerateSalt();
            Hash = ComputeHash(password, Salt);
        }

        public Password()
        {
        }

        #endregion

        #region Public methods

        /// <summary>
        /// Returns true if this password is the same as given password
        /// </summary>
        public bool VerifyPassword(string password)
        {
            byte[] computedHash = ComputeHash(password, Salt);
            return Hash.SequenceEqual(computedHash);
        }

        #endregion

        private static byte[] ComputeHash(string password, byte[] salt)
        {
            byte[] passwordBytes = _encoding.GetBytes(password);
            byte[] hashInputBytes = passwordBytes.Concat(salt).ToArray();
            byte[] hashOutputBytes = ComputeHash(hashInputBytes);

            return hashOutputBytes;
        }

        private static byte[] ComputeHash(byte[] input)
        {
            using (var hasher = new SHA512Managed())
            {
                byte[] hashBytes = hasher.ComputeHash(input);
                return hashBytes;
            }
        }

        private static byte[] GenerateSalt()
        {
            var saltBytes = new byte[SaltLength];
            using (var randomGenerator = new RNGCryptoServiceProvider())
            {
                randomGenerator.GetBytes(saltBytes);
            }
            return saltBytes;
        }
    }
}