Data commit

Task/SQL-based-authentication/Kotlin/sql-based-authentication.kotlin

@@ -0,0 +1,101 @@
+// Version 1.2.41
+
+import java.sql.Connection
+import java.sql.DriverManager
+import java.sql.ResultSet
+import java.security.MessageDigest
+import java.security.SecureRandom
+import java.math.BigInteger
+
+class UserManager {
+    private lateinit var dbConnection: Connection
+
+    private fun md5(message: String): String {
+        val hexString = StringBuilder()
+        val bytes = message.toByteArray()
+        val md = MessageDigest.getInstance("MD5")
+        val dig = md.digest(bytes)
+        for (i in 0 until dig.size) {
+            val hex = (0xff and dig[i].toInt()).toString(16)
+            if (hex.length == 1) hexString.append('0')
+            hexString.append(hex)
+        }
+        return hexString.toString()
+    }
+
+    fun connectDB(host: String, port: Int, db: String, user: String, pwd: String) {
+        Class.forName("com.mysql.jdbc.Driver")
+        dbConnection = DriverManager.getConnection(
+            "jdbc:mysql://$host:$port/$db", user, pwd
+        )
+    }
+
+    fun createUser(user: String, pwd: String): Boolean {
+        val random = SecureRandom()
+        val salt = BigInteger(130, random).toString(16)
+        val insert = "INSERT INTO users " +
+            "(username, pass_salt, pass_md5) " +
+            "VALUES (?, ?, ?)"
+        try {
+            val pstmt = dbConnection.prepareStatement(insert)
+            with (pstmt) {
+                setString(1, user)
+                setString(2, salt)
+                setString(3, md5(salt + pwd))
+                val rowCount = executeUpdate()
+                close()
+                if (rowCount == 0) return false
+            }
+            return true
+        }
+        catch (ex: Exception) {
+            return false
+        }
+    }
+
+    fun authenticateUser(user: String, pwd: String): Boolean {
+        val select = "SELECT pass_salt, pass_md5 FROM users WHERE username = ?"
+        lateinit var res: ResultSet
+        try {
+            val pstmt = dbConnection.prepareStatement(select)
+            with (pstmt) {
+                setString(1, user)
+                res = executeQuery()
+                res.next()  // assuming that username is unique
+                val passSalt = res.getString(1)
+                val passMD5  = res.getString(2)
+                close()
+                return passMD5 == md5(passSalt + pwd)
+            }
+        }
+        catch (ex: Exception) {
+            return false
+        }
+        finally {
+            if (!res.isClosed) res.close()
+        }
+    }
+
+    fun closeConnection() {
+        if (!dbConnection.isClosed) dbConnection.close()
+    }
+}
+
+fun main(args: Array<String>) {
+    val um = UserManager()
+    with (um) {
+        try {
+            connectDB("localhost", 3306, "test", "root", "admin")
+            if (createUser("johndoe", "test")) println("User created")
+            if (authenticateUser("johndoe", "test")) {
+                println("User authenticated")
+            }
+        }
+        catch(ex: Exception) {
+            ex.printStackTrace()
+        }
+        finally {
+            closeConnection()
+        }
+    }
+}