aes.go

package kuu

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"errors"
	"io"
)

// PKCS7Padding
func PKCS7Padding(ciphertext []byte, blockSize int) []byte {
	padding := blockSize - len(ciphertext)%blockSize
	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(ciphertext, padtext...)
}

// PKCS7UnPadding
func PKCS7UnPadding(origData []byte) []byte {
	length := len(origData)
	unpadding := int(origData[length-1])
	return origData[:(length - unpadding)]
}

// AESCBCEncrypt 填充秘钥key的16位（24、32分别对应AES-128、AES-192或AES-256）
func AESCBCEncrypt(rawData, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	// 填充原文
	blockSize := block.BlockSize()
	rawData = PKCS7Padding(rawData, blockSize)
	// 初始向量IV必须是唯一，但不需要保密
	cipherText := make([]byte, blockSize+len(rawData))
	// block大小 16
	iv := cipherText[:blockSize]
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		return nil, err
	}

	// block大小和初始向量大小一定要一致
	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(cipherText[blockSize:], rawData)

	return cipherText, nil
}

// AESCBCDecrypt
func AESCBCDecrypt(encryptData, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	blockSize := block.BlockSize()

	if len(encryptData) < blockSize {
		return nil, errors.New("ciphertext too short")
	}
	iv := encryptData[:blockSize]
	encryptData = encryptData[blockSize:]

	// CBC mode always works in whole blocks.
	if len(encryptData)%blockSize != 0 {
		return nil, errors.New("ciphertext is not a multiple of the block size")
	}

	mode := cipher.NewCBCDecrypter(block, iv)

	// CryptBlocks can work in-place if the two arguments are the same.
	mode.CryptBlocks(encryptData, encryptData)
	encryptData = PKCS7UnPadding(encryptData)
	return encryptData, nil
}