In the Ch11_CryptographyLib class library project, add a new class named User. This will represent a user stored in memory, a file, or a database:

    namespace Packt.CS7 
    { 
      public class User 
      { 
        public string Name { get; set; } 
        public string Salt { get; set; } 
        public string SaltedHashedPassword { get; set; } 
      } 
    } 

Add the following code to the Protector class. We will use a dictionary to store multiple users in memory. There are two methods, one to register a new user and one to validate their password when they subsequently log in:

    private static Dictionary<string, User> Users =  
      new Dictionary<string, User>(); 
 
    public static User Register(string username, string password) 
    { 
      // generate a random salt 
      var rng = RandomNumberGenerator.Create(); 
      var saltBytes = new byte[16]; 
      rng.GetBytes(saltBytes); 
      var saltText = Convert.ToBase64String(saltBytes); 
 
      // generate the salted and hashed password 
      var sha = SHA256.Create(); 
      var saltedPassword = password + saltText; 
      var saltedhashedPassword = Convert.ToBase64String( 
        sha.ComputeHash(Encoding.Unicode.GetBytes(saltedPassword))); 
 
      var user = new User 
      { 
        Name = username, 
        Salt = saltText, 
        SaltedHashedPassword = saltedhashedPassword 
      }; 
      Users.Add(user.Name, user); 
 
      return user; 
    } 
 
    public static bool CheckPassword(string username, string password) 
    { 
      if (!Users.ContainsKey(username)) 
      { 
        return false; 
      } 
      var user = Users[username]; 
 
      // re-generate the salted and hashed password 
      var sha = SHA256.Create(); 
      var saltedPassword = password + user.Salt; 
      var saltedhashedPassword = Convert.ToBase64String( 
        sha.ComputeHash(Encoding.Unicode.GetBytes(saltedPassword))); 
 
      return (saltedhashedPassword == user.SaltedHashedPassword); 
    } 

Add a new console application project named Ch11_HashingApp. Add a reference to the Ch11_CryptographyLib assembly as you did before, and then import the following namespace and type:

    using Packt.CS7; 
    using static System.Console; 

In the Main method, add the following statements to register a user and prompt to register a second user, and then prompt to log in as one of those users and validate the password:

    WriteLine("A user named Alice has been registered with Pa$$w0rd as
    her password."); 
    var alice = Protector.Register("Alice", "Pa$$w0rd"); 
    WriteLine($"Name: {alice.Name}"); 
    WriteLine($"Salt: {alice.Salt}"); 
    WriteLine( 
      $"Salted and hashed password: {alice.SaltedHashedPassword}"); 
    WriteLine(); 
    Write("Enter a different username to register: "); 
    string username = ReadLine(); 
    Write("Enter a password to register: "); 
    string password = ReadLine(); 
    var user = Protector.Register(username, password); 
    WriteLine($"Name: {user.Name}"); 
    WriteLine($"Salt: {user.Salt}"); 
    WriteLine( 
      $"Salted and hashed password: {user.SaltedHashedPassword}"); 
 
    bool correctPassword = false; 
    while (!correctPassword) 
    { 
      Write("Enter a username to log in: "); 
      string loginUsername = ReadLine(); 
      Write("Enter a password to log in: "); 
      string loginPassword = ReadLine(); 
      correctPassword = Protector.CheckPassword( 
        loginUsername, loginPassword); 
         if (correctPassword) 
      { 
        WriteLine( 
          $"Correct! {loginUsername} has been logged in."); 
      } 
      else 
      { 
        WriteLine("Invalid username or password. Try again."); 
      } 
    } 

Run the console application and view the output:

A user named Alice has been registered with Pa$$w0rd as her password.
Name: Alice
Salt: tLn3gRn9DXmp2oeuvBSxTg==
Salted and hashed password:
  w8Ub2aH5NNQ8MJarYsUgm29bbbl0lV/9dlozjWs2Ipk=
Enter a different username to register: Bob
Enter a password to register: Pa$$w0rd
Name: Bob
Salt: zPU9YyFLaz0idhQkKpzY+g==
Salted and hashed password:
  8w14w8WNHoZddEeIx2+UJhpHQqSs4EmyoazqjbmmEz0=
Enter a username to log in: Bob
Enter a password to log in: secret
Invalid username or password. Try again.
Enter a username to log in: Alice
Enter a password to log in: secret
Invalid username or password. Try again.
Enter a username to log in: Bob
Enter a password to log in: Pa$$w0rd
Correct! Bob has been logged in.