iOS DES解密，key位16位时，解密出来位nil

密文 ： 429473191145312278382171352981058688
key ： 6568535557566965
后台的偏移量和key是一样的 我就写成这样了 Byte iv[] = {65,68,53,55,57,56,69,65};

下面是我解密方法里面的方法：

• (NSString ) decryptUseDES:(NSString)cipherText key:(NSString*)key
  {

// NSData* cipherData = [GTMBase64 decodeString:cipherText];

NSData* cipherData = [GTMBase64 decodeData:[cipherText dataUsingEncoding:NSUTF8StringEncoding]];
unsigned char buffer[1024];

memset(buffer, 0, sizeof(char));

size_t numBytesDecrypted = 0;
Byte iv[] = {65,68,53,55,57,56,69,65};
CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt,
                                      kCCAlgorithmDES,
                                      kCCOptionPKCS7Padding| kCCOptionECBMode,
                                      [key UTF8String],
                                      kCCKeySizeDES,
                                      iv,
                                      [cipherData bytes],
                                      [cipherData length],
                                      buffer,
                                      1024,
                                      &numBytesDecrypted);
NSString* plainText = nil;
if (cryptStatus == kCCSuccess) {
    NSData* data = [NSData dataWithBytes:buffer length:(NSUInteger)numBytesDecrypted];
    
    plainText = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
}
return plainText;

}