NSData to NSString random characters

NSData to NSString random characters

when i log the vaule for responseString below, it always has random
characters - is that a php issue or an ios issue?
NSURLResponse *response;
NSError *error;
NSData *responseData = [NSURLConnection sendSynchronousRequest:request
returningResponse:&response error:&error];
NSString *responseString = [NSString stringWithUTF8String:[responseData
bytes]];
NSLog(@"%@", responseString);
NSString *success = @"200200";
[success dataUsingEncoding:NSUTF8StringEncoding];
NSLog(@"%lu", (unsigned long)responseString.length);
NSLog(@"%lu", (unsigned long)success.length);
//responseString.length should = success.length but doesn't :(