Initial data commit

Task/SQL-based-authentication/C-sharp/sql-based-authentication-1.cs

@@ -0,0 +1,38 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace rosettaMySQL
+{
+    class Hasher
+    {
+        private static string _BytesToHex(byte[] input)
+        {
+            var strBuilder = new StringBuilder();
+            foreach (byte _byte in input)
+            {
+                strBuilder.Append(_byte.ToString("x2"));
+            }
+            return strBuilder.ToString();
+        }
+
+        public static string Hash(string salt, string input)
+        {
+            using (MD5 md5 = new MD5CryptoServiceProvider())
+            {
+                var bytes = Encoding.Default.GetBytes(salt + input);
+                var data = md5.ComputeHash(bytes);
+                return _BytesToHex(data);
+            }
+        }
+
+        public static string GenSalt()
+        {
+            using (RandomNumberGenerator rng = new RNGCryptoServiceProvider())
+            {
+                var salt = new byte[16];
+                rng.GetBytes(salt);
+                return _BytesToHex(salt);
+            }
+        }
+    }
+}

Task/SQL-based-authentication/C-sharp/sql-based-authentication-2.cs

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+using MySql.Data.MySqlClient;
+
+namespace rosettaMySQL
+{
+    class UserOperator
+    {
+        private MySqlConnection _connection;
+
+        public UserOperator(MySqlConnection connection)
+        {
+            _connection = connection;
+        }
+
+        public bool CreateUser(string username, string password)
+        {
+            try
+            {
+                var salt = Hasher.GenSalt();
+                var hash = Hasher.Hash(salt, password);
+                var sql = $"INSERT INTO users " +
+                          $"(username, pass_salt, pass_md5) " +
+                          $"VALUES ('{username}','{salt}','{hash}')";
+                using (var command = new MySqlCommand(sql, _connection))
+                {
+                    command.ExecuteNonQuery();
+                    return true;
+                }
+            }
+            catch (MySqlException e)
+            {
+                if (e.Number == 1062) //username is a duplicate
+                {
+                    return false;
+                }
+                else
+                {
+                    throw e;
+                }
+            }
+        }
+
+        public bool AuthenticateUser(string username, string password)
+        {
+            var sql = $"SELECT userid, username, pass_salt, pass_md5 " +
+                      $"FROM users " +
+                      $"WHERE username='{username}';";
+
+            using (var command = new MySqlCommand(sql, _connection))
+            using (var reader = command.ExecuteReader())
+            {
+                if (reader.HasRows)
+                {
+                    reader.Read();
+                    var salt = reader.GetString("pass_salt");
+                    var hash = reader.GetString("pass_md5");
+                    return (Hasher.Hash(salt, password) == hash);
+                }
+                else
+                {
+                    return false;
+                }
+            }
+        }
+    }
+}

Task/SQL-based-authentication/C-sharp/sql-based-authentication-3.cs

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+using System;
+using MySql.Data.MySqlClient;
+
+namespace rosettaMySQL
+{
+    class Program
+    {
+        public static MySqlConnection ConnectDB(string server, int port, string db,
+                                                string username, string password)
+        {
+            var connectStr = $"server={server};" +
+                             $"user={username};" +
+                             $"database={db};" +
+                             $"port={port};" +
+                             $"password={password}";
+            return new MySqlConnection(connectStr);
+        }
+
+        static void Main(string[] args)
+        {
+            try
+            {
+                var connection = ConnectDB("localhost", 3306, "test", "root", "password");
+                connection.Open();
+                var userOperator = new UserOperator(connection);
+                Console.WriteLine("Bob has been created: " + userOperator.CreateUser("Bob", "123456"));
+                Console.WriteLine("Bob has been duplicated: " + userOperator.CreateUser("Bob", "123456"));
+                Console.WriteLine("Wrong password works: " + userOperator.AuthenticateUser("BOB", "notpassword"));
+                Console.WriteLine("Right password works: " + userOperator.AuthenticateUser("BOB", "123456"));
+            }
+            catch(MySqlException e)
+            {
+                switch(e.Number)
+                {
+                    case 0:
+                        Console.WriteLine("Cannot connect to server");
+                        break;
+                    case 1045:
+                        Console.WriteLine("Invalid database username/password");
+                        break;
+                    default:
+                        Console.WriteLine(e.ToString());
+                        Console.WriteLine(e.Number);
+                        break;
+                }
+            }
+            catch (Exception e)
+            {
+                Console.WriteLine(e.ToString());
+            }
+        }
+    }
+}