原来的加密解密是用java写的，用在安卓系统上。现在要用在iOS系统上，所以从服务器上下载过来的加密文件要用swift来实现其的解密方法。

具体过程如下：

给NSData增加一个类目，NSData+AES

NSData+AES.h

- (NSData *)AES128DecryptWithKey:(NSString *)key iv:(NSData *)iv;

NSData+AES.m

- (NSData *)AES128operation:(CCOperation)operation key:(NSString *)key iv:(NSData *)iv

{

    char keyPtr[kCCKeySizeAES128 + 1];

    bzero(keyPtr, sizeof(keyPtr));

    [key getCString:keyPtr maxLength:sizeof(keyPtr) encoding:NSUTF8StringEncoding];

    Byte key2[] = {0xF0,0x1E,0x02,0xB2,0xE3,0xC9,0x7A,0x43,0xFD,0xFE,0x31,0x1A,0x2B,0xA4,0x4C,0x60};

    // IV

    Byte ivPtr[kCCBlockSizeAES128 + 1];

    bzero(ivPtr, sizeof(ivPtr));

    //[iv getCString:ivPtr maxLength:sizeof(ivPtr) encoding:NSUTF8StringEncoding];

    [iv getBytes:&ivPtr length:16];

    size_t bufferSize = [self length] + kCCBlockSizeAES128;

    void *buffer = malloc(bufferSize);

    size_t numBytesEncrypted = 0;

    CCCryptorStatus cryptorStatus = CCCrypt(operation, kCCAlgorithmAES128, kCCOptionPKCS7Padding,

                                            key2, kCCKeySizeAES128,

                                            ivPtr,

                                            [self bytes], [self length],

                                            buffer, bufferSize,

                                            &numBytesEncrypted);

    if(cryptorStatus == kCCSuccess){

        NSLog(@"Success");

        return [NSData dataWithBytesNoCopy:buffer length:numBytesEncrypted];

    }else{

        NSLog(@"Error");

    }

    free(buffer);

    return nil;

}