[Kotlin] 암호화와 복호화

암호화 (AES256, BLOWFISH)

복호화

---

Hash 함수를 통과 하기전의 원본 데이터를 메시지(message)라고 부르고, 통과된 이후의 데이터를 다이제스트(digest)라고 부른다.

 

1. AES/ECB/PKCS5PADDING 방식

키

plaintext

cipher

ciphertext

 

2. AES/CBC/PKCS5PADDING 방식

키

iv

plaintext

cipher

ciphertext

 

3. key값의 길이에 따라 AES128, AES192, AES256 으로 구분됨

    AES128 : 키값 16bytes

    AES192 : 키값 24bytes

    AES256 : 키값 32bytes

---

MainActivity.kt

package com.example.encryptionexample

import android.os.Bundle
import android.util.Base64
import android.util.Log
import androidx.appcompat.app.AppCompatActivity
import javax.crypto.Cipher
import javax.crypto.spec.IvParameterSpec
import javax.crypto.spec.SecretKeySpec

class MainActivity : AppCompatActivity() {

    companion object {
        const val SECRET_KEY = "ABCDEFGH12345678"
        const val SECRET_IV = "1234567812345678"
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val encrypted = "안녕하세요!!!".encryptECB()
        val decrypted = encrypted.decryptECB()

        Log.e("", encrypted)
        Log.e("", decrypted)

        val encryptedCBC = "Hello~!!!".encryptCBC()
        val decryptedCBC = encryptedCBC.decryptCBC()

        Log.e("", encryptedCBC)
        Log.e("", decryptedCBC)
    }

    /**
     * ECB 암호화
     */
    private fun String.encryptECB(): String{
        val keySpec = SecretKeySpec(SECRET_KEY.toByteArray(), "AES")    /// 키
        val cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING")     //싸이퍼
        cipher.init(Cipher.ENCRYPT_MODE, keySpec)       // 암호화/복호화 모드
        val ciphertext = cipher.doFinal(this.toByteArray())
        val encodedByte = Base64.encode(ciphertext, Base64.DEFAULT)
        return String(encodedByte)
    }

    /**
     * ECB 복호화
     */
    private fun String.decryptECB(): String {
        val keySpec = SecretKeySpec(SECRET_KEY.toByteArray(), "AES")
        var decodedByte: ByteArray = Base64.decode(this, Base64.DEFAULT)
        val cipher = Cipher.getInstance("AES/ECB/PKCS5PADDING")
        cipher.init(Cipher.DECRYPT_MODE, keySpec)
        val output = cipher.doFinal(decodedByte)

        return String(output)
    }

    /**
     * CBC 암호화
     */
    private fun String.encryptCBC(): String{
        val iv = IvParameterSpec(SECRET_IV.toByteArray())
        val keySpec = SecretKeySpec(SECRET_KEY.toByteArray(), "AES")    /// 키
        val cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING")     //싸이퍼
        cipher.init(Cipher.ENCRYPT_MODE, keySpec, iv)       // 암호화/복호화 모드
        val crypted = cipher.doFinal(this.toByteArray())
        val encodedByte = Base64.encode(crypted, Base64.DEFAULT)

        return String(encodedByte)
    }

    /**
     * CBC 복호화
     */
    private fun String.decryptCBC(): String {
        var decodedByte: ByteArray = Base64.decode(this, Base64.DEFAULT)
        val iv = IvParameterSpec(SECRET_IV.toByteArray())
        val keySpec = SecretKeySpec(SECRET_KEY.toByteArray(), "AES")
        val cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING")
        cipher.init(Cipher.DECRYPT_MODE, keySpec, iv)
        val output = cipher.doFinal(decodedByte)

        return String(output)
    }

}

실행 결과

 

 

 

 

 

 

참고.

https://developer.android.com/guide/topics/security/cryptography?hl=ko 

암호화  |  Android 개발자  |  Android Developers

 

Encoding ? Enctyption ?

https://stackoverflow.com/questions/4657416/difference-between-encoding-and-encryption

Difference between encoding and encryption

 

CBC? ECB?

https://m.blog.naver.com/PostView.naver?isHttpsRedirect=true&blogId=jsky10503&logNo=221258926405 

블록암호와 운용방식(ECB, CBC, CTR)

http://happinessoncode.com/2019/04/06/java-cipher-algorithm-mode-padding/

Java Cipher - 알고리즘, 운용 모드, 패딩의 이해