/*加密方法*/
 (NSString *)AES256EncryptWithPlainText:(NSString *)plain {
 NSData *plainText = [plain dataUsingEncoding:NSUTF8StringEncoding];
 // ´key´ should be 32 bytes for AES256, will be null-padded otherwise
 char keyPtr[kCCKeySizeAES256 1]; // room for terminator (unused)
 bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
  
 NSUInteger dataLength = [plainText length];

 size_t bufferSize = dataLength kCCBlockSizeAES128;
 void *buffer = malloc(bufferSize);
 bzero(buffer, sizeof(buffer));
 
 size_t numBytesEncrypted = 0;
 
 CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmAES128,kCCOptionPKCS7Padding,
           [[NSData AESKeyForPassword:PASSWORD] bytes], kCCKeySizeAES256,
           ivBuff /* initialization vector (optional) */,
           [plainText bytes], dataLength, /* input */
           buffer, bufferSize, /* output */
           &numBytesEncrypted);
 if (cryptStatus == kCCSuccess) {
  NSData *encryptData = [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];
  return [encryptData base64Encoding];
 }
 
 free(buffer); //free the buffer;
 return nil;
}

/*解密方法*/
 (NSString *)AES256DecryptWithCiphertext:(NSString *)ciphertexts{
 
 NSData *cipherData = [NSData dataWithBase64EncodedString:ciphertexts];
 // ´key´ should be 32 bytes for AES256, will be null-padded otherwise
 char keyPtr[kCCKeySizeAES256 1]; // room for terminator (unused)
 bzero(keyPtr, sizeof(keyPtr)); // fill with zeroes (for padding)
  
 NSUInteger dataLength = [cipherData length];
 
 size_t bufferSize = dataLength kCCBlockSizeAES128;
 void *buffer = malloc(bufferSize);
  
 size_t numBytesDecrypted = 0;
 CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt, kCCAlgorithmAES128, kCCOptionPKCS7Padding,
           [[NSData AESKeyForPassword:PASSWORD] bytes], kCCKeySizeAES256, 
           ivBuff ,/* initialization vector (optional) */
           [cipherData bytes], dataLength, /* input */
           buffer, bufferSize, /* output */
           &numBytesDecrypted);
 
 if (cryptStatus == kCCSuccess) {
  NSData *encryptData = [NSData dataWithBytesNoCopy:buffer length:numBytesDecrypted];
  return [[[NSString alloc] initWithData:encryptData encoding:NSUTF8StringEncoding] init];
 }
 
 free(buffer); //free the buffer;
 return nil;
}

private byte[] encrypt(String cmp, SecretKey sk, IvParameterSpec IV,
  byte[] msg) {
 try {
  Cipher c = Cipher.getInstance(cmp);
  c.init(Cipher.ENCRYPT_MODE, sk, IV);
  return c.doFinal(msg);
 } catch (NoSuchAlgorithmException nsae) {
  Log.e("AESdemo", "no cipher getinstance support for " cmp);
 } catch (NoSuchPaddingException nspe) {
  Log.e("AESdemo", "no cipher getinstance support for padding " cmp);
 } catch (InvalidKeyException e) {
  Log.e("AESdemo", "invalid key exception");
 } catch (InvalidAlgorithmParameterException e) {
  Log.e("AESdemo", "invalid algorithm parameter exception");
 } catch (IllegalBlockSizeException e) {
  Log.e("AESdemo", "illegal block size exception");
 } catch (BadPaddingException e) {
  Log.e("AESdemo", "bad padding exception");
 }
 return null;
}

private byte[] decrypt(String cmp, SecretKey sk, IvParameterSpec IV,
   byte[] ciphertext) {
 try {
  Cipher c = Cipher.getInstance(cmp);
  c.init(Cipher.DECRYPT_MODE, sk, IV);
  return c.doFinal(ciphertext);
 } catch (NoSuchAlgorithmException nsae) {
  Log.e("AESdemo", "no cipher getinstance support for " cmp);
 } catch (NoSuchPaddingException nspe) {
  Log.e("AESdemo", "no cipher getinstance support for padding " cmp);
 } catch (InvalidKeyException e) {
  Log.e("AESdemo", "invalid key exception");
 } catch (InvalidAlgorithmParameterException e) {
  Log.e("AESdemo", "invalid algorithm parameter exception");
 } catch (IllegalBlockSizeException e) {
  Log.e("AESdemo", "illegal block size exception");
 } catch (BadPaddingException e) {
  Log.e("AESdemo", "bad padding exception");
  e.printStackTrace();
 }
 return null;
}