package main

import (
    "bytes"
    "crypto/aes"
    "crypto/cipher"
    "encoding/base64"
    "fmt"
)

func main() {
    testAes()
}

func testAes() {
    // AES-128。key長度：16, 24, 32 bytes 對應 AES-128, AES-192, AES-256
    key := []byte("[email protected]")
    result, err := AesEncrypt([]byte("[email protected]
 
"), key)
    if err != nil {
        panic(err)
    }
    fmt.Println(base64.StdEncoding.EncodeToString(result))
    origData, err := AesDecrypt(result, key)
    if err != nil {
        panic(err)
    }
    fmt.Println(string(origData))
}

func AesEncrypt(origData, key []byte) ([]byte, error) {
    block, err := aes.NewCipher(key)
    if
 
 err != nil {
        return nil, err
    }
    blockSize := block.BlockSize()
    origData = PKCS5Padding(origData, blockSize)
    // origData = ZeroPadding(origData, block.BlockSize())
    blockMode := cipher.NewCBCEncrypter(block, key[:blockSize])
    crypted := make([]byte, len(origData))
    // 根據CryptBlocks方法的說明，如下方式初始化crypted也可以
 

    // crypted := origData
    blockMode.CryptBlocks(crypted, origData)
    return crypted, nil
}

func AesDecrypt(crypted, key []byte) ([]byte, error) {
    block, err := aes.NewCipher(key)
    if err != nil {
        return nil, err
    }
    blockSize := block.BlockSize()
    blockMode := cipher.NewCBCDecrypter(block, key[:blockSize])
    origData := make([]byte, len(crypted))
    // origData := crypted
    blockMode.CryptBlocks(origData, crypted)
    origData = PKCS5UnPadding(origData)
    // origData = ZeroUnPadding(origData)
    return origData, nil
}

func ZeroPadding(ciphertext []byte, blockSize int) []byte {
    padding := blockSize - len(ciphertext)%blockSize
    padtext := bytes.Repeat([]byte{0}, padding)
    return append(ciphertext, padtext...)
}

func ZeroUnPadding(origData []byte) []byte {
    length := len(origData)
    unpadding := int(origData[length-1])
    return origData[:(length - unpadding)]
}

func PKCS5Padding(ciphertext []byte, blockSize int) []byte {
    padding := blockSize - len(ciphertext)%blockSize
    padtext := bytes.Repeat([]byte{byte(padding)}, padding)
    return append(ciphertext, padtext...)
}

func PKCS5UnPadding(origData []byte) []byte {
    length := len(origData)
    // 去掉最後一個位元組 unpadding 次
    unpadding := int(origData[length-1])
    return origData[:(length - unpadding)]
}