queue1 = dispatch_queue_create("com..queue1", DISPATCH_QUEUE_CONCURRENT);



for(NSDictionary *dictInfo in dataArray){
      dispatch_async(queue1,^(void){
       [[HeaderValueGenerator sharedInstance] createSignature];
     }

}

+ (HeaderValueGenerator *)sharedInstance {
static HeaderValueGenerator *sharedInstance = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
    instance = [[self alloc] init];
});    return sharedInstance;
}

-(void)createSignature{
   //string hashing and data encoding the header values for special header fields

 }