java aes CBC的填充方式發現

以下的java代碼，手動對block進行填充後，使其爲16的整數倍後，加密的時候居然強行再填充了16位，我在嘗試用golang實現這段加密時，反覆修改了好久，發現golang版的老是比java加密出來並base64的結果少了20位，因而把各個步驟中間結果打出來，發現並無什麼不一樣，而後嘗試在golang後面強行追加了16個填充，那麼填充什麼呢？沒錯，我就是從0x0到0x10一個一個試出來的，最後發現當填充16個0x10時，golang跟java的加密結果就徹底同樣了，實際上是按照pkcs5的填充規則的，例如須要填充n位，那麼填充的值就是n，下面貼出golang跟java的兩個代碼：

PS: iv和key都是如出一轍的。獲得一個教訓，當golang跟java在兩種相同的模式下面若是加密出來的密文不一樣的時候就去嘗試修改填充的方法吧，多嘗試幾回老是能夠的。

java:

public static String aesEncrypt2(String appsecret, String data) throws Exception
    {
        //設置加密密鑰
        String key = appsecret.substring(16);
        System.out.println(key);
        SecretKeySpec keyspec = new SecretKeySpec(key.getBytes(), "AES");
        //初始化向量
        System.out.println("md5: " + DigestUtils.md5Hex(appsecret).substring(0, 16));
        String iv = DigestUtils.md5Hex(appsecret).substring(0, 16);
        IvParameterSpec ivspec = new IvParameterSpec(iv.getBytes());
        //設置加密模式
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        //填充算法
        int blockSize = cipher.getBlockSize();
        byte[] dataBytes = data.getBytes();
        int plaintextLength = dataBytes.length;
        if (plaintextLength % blockSize != 0) {
            plaintextLength = plaintextLength + (blockSize - (plaintextLength % blockSize));
        }
        byte[] plaintext = new byte[plaintextLength];
        System.arraycopy(dataBytes, 0, plaintext, 0, dataBytes.length);
        System.out.println("填充後長度=" + plaintext.length);
        for(int i = 0;i < plaintext.length; i++)
        System.out.print(plaintext[i] + " ");
        //加密
        cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivspec);
        byte[] encrypted = cipher.doFinal(plaintext);
        System.out.println("");
        for(int i = 0;i < encrypted.length;i++)
            System.out.print(encrypted[i] + " ");
        System.out.println("");
        return Base64.encodeBase64String(encrypted);
    }

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golang:

func GetMD5(cipherText string) string {
    md5Ctx := md5.New()
    md5Ctx.Write([]byte(cipherText))
    cipherStr := md5Ctx.Sum(nil)
    return hex.EncodeToString(cipherStr)
}


func PKCS5Padding(ciphertext []byte, blockSize int) []byte {
    padding := blockSize - len(ciphertext)%blockSize
    //    padtext := bytes.Repeat([]byte{byte(padding)}, padding)
    for i := 0; i < padding; i++ {
        ciphertext = append(ciphertext, 0x0)
    }
    for i := 16; i < 32; i++ {
        ciphertext = append(ciphertext, 0x10)
    }
    fmt.Println(ciphertext)
    fmt.Printf("blocksieze[%d]\n", len(ciphertext))
    //    return append(ciphertext, padtext...)
    return ciphertext
}

func AesEncrypt(secret, data string) string {
    if len(secret) < 16 {
        log.Errorf("AesEncrypt secret[%s] length less 16")
        return ""
    }
    fmt.Println(secret[16:])
    key := []byte(secret[16:])
    iv := []byte(GetMD5(secret)[:16])
    fmt.Println("md5: " + GetMD5(secret)[:16])
    block, err := aes.NewCipher(key)
    if err != nil {
        log.Errorf("key error[%v]", err)
        return ""
    }
    ecb := cipher.NewCBCEncrypter(block, iv)
    content := PKCS5Padding([]byte(data), block.BlockSize())
    crypted := make([]byte, len(content))
    ecb.CryptBlocks(crypted, content)
    fmt.Println(crypted)
    return base64.StdEncoding.EncodeToString(crypted)
}

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