异或

  /*
    NSData *keyData = [@"woshikey" dataUsingEncoding:NSUTF8StringEncoding];
    NSData *encodedata = [self xorData:data  withKey:keyData];
  */
- (NSData *)xorData:(NSData *)sourceData withKey:(NSData *)keyData {
    //取关键字的Byte数组
    Byte *keyBytes = (Byte *)[keyData bytes]; 
    //取需要加密的数据的Byte数组
    Byte *sourcePoint = (Byte *)[sourceData bytes]; 
    for (long i = 0; i < [sourceData length]; i++) {
        // key可以任意长度
        long index = i % [keyData length];
        // NSLog(@"%ld index=%ld",i,index);
        //然后按位进行异或运算
        sourcePoint[i] = sourcePoint[i] ^ keyBytes[index]; 
    }
    return sourceData;
}