aes.go

package crypt

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

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

func PKCS5UnPadding(src []byte, block_size int) ([]byte, error) {
	length := len(src)
	padding := int(src[length-1])
	if padding < 0 || padding > length {
		return nil, errors.New("PKCS5UnPadding error")
	}
	return src[:length-padding], nil
}

func Encrypt(block cipher.Block, plaintext []byte, key []byte) ([]byte, error) {
	block_size := block.BlockSize()
	plaintext = PKCS5Padding(plaintext, block_size)

	ciphertext := make([]byte, block_size+len(plaintext))
	iv := ciphertext[:block_size]
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		return nil, err
	}

	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(ciphertext[block_size:], plaintext)

	return ciphertext, nil
}

func Decrypt(block cipher.Block, ciphertext []byte, key []byte) ([]byte, error) {
	block_size := block.BlockSize()

	if len(ciphertext) < block_size {
		return nil, errors.New("Decrypt failed: uncomplete ciphertext")
	}
	iv := ciphertext[:block_size]
	ciphertext = ciphertext[block_size:]

	mode := cipher.NewCBCDecrypter(block, iv)
	mode.CryptBlocks(ciphertext, ciphertext)

	return PKCS5UnPadding(ciphertext, block_size)
}

func AesEncrypt(plaintext []byte, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	return Encrypt(block, plaintext, key)
}

func AesDecrypt(ciphertext []byte, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	return Decrypt(block, ciphertext, key)
}