A curious way to decrypt a text (like a mobile-phone number) - if you know the key ;-)

DecryptApp.scala

import java.util.Base64
import javax.crypto.Cipher
import javax.crypto.spec.SecretKeySpec
import scala.io.StdIn

object DecryptApp extends App {

  object Decrypter {

    private val decoder = Base64.getDecoder

    def decrypt(text: String, key: String): String = {
      val encryptedDecoded = decoder.decode(text)
      new String(cipher(key).doFinal(encryptedDecoded))
    }

    private def cipher(key: String) = {
      val cipher = Cipher.getInstance("AES")
      val aesKey = new SecretKeySpec(key.getBytes, "AES")
      cipher.init(Cipher.DECRYPT_MODE, aesKey)
      cipher
    }

  }

  // Key has to be 16 bytes long, with first_name + "___" + last_name
  def buildKey(input: String): String = {
    val Array(firstName, lastName) = 
      input
        .split(" ")
        .map(_.trim)
        .map(_.toLowerCase)
        .map(_.capitalize)
    firstName + "___" + lastName
  }

  val key = {
    val input = StdIn.readLine("Who created Scala (hint: M.... Od.....) ?")
    buildKey(input)
  }

  val encrypted = StdIn.readLine("Enter text to decrypt: ")

  println("Decrypted text is: " + Decrypter.decrypt(encrypted, key))
}