iOS cocoaAsyncSocket get data parse String return null

Question

I try to connect telnet to my telnet server port 23 in iOS.

I use the "cocoaAsyncSocket" library.

I can received the data from the telnet.

But I try to decode to the string , the data is not my expect.

It will show

 (null)

If I use NSASCIIStringEncodeing　to decode.

It will show

 ÿýÿý ÿý#ÿý'

I use the terminal command, telnet myIP 23.

I can get below in terminal.

  james$ telnet 192.168.2.94 23
 Trying 192.168.2.94...
 Conn ected to txxxxx.xxxxx.com.
 Escape character is '^]'.
 Password: 

how can I parse to the "Password:" string in iOS?

thank you .

my connect code below:

 - (void)viewDidLoad {
     [super viewDidLoad];
     asyncSocket = [[GCDAsyncSocket alloc] initWithDelegate:self    delegateQueue:dispatch_get_main_queue()];

     buffer = [[NSMutableData alloc] init];
      [asyncSocket connectToHost:@"192.168.2.94" onPort:23 error:nil];
 }

 - (void)socket:(GCDAsyncSocket *)sock didConnectToHost:(NSString *)host port:(uint16_t)port{
     NSLog(@"did connect to host");
      [asyncSocket readDataWithTimeout:-1 tag:0];
 }

 - (void)socket:(GCDAsyncSocket *)sock didReadData:(NSData *)data withTag:(long)tag {
          NSLog(@"didReadData(%lu): %@", tag, @([data length]));
          [buffer setLength:0];

      NSString* message = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
 //            NSString* message = [[NSString alloc] initWithData:data  encoding:NSUTF8StringEncoding];
     NSLog(@"message is: \n%@",message);



     [asyncSocket readDataWithTimeout:-1 buffer:buffer bufferOffset:[buffer length] tag:tag];
 }

 - (void)socketDidDisconnect:(GCDAsyncSocket *)sock withError:(NSError *)err
 {
   NSLog(@"socket disconnect to host");

 }