Setting SSL or TLS security on NSStream

I have a networking code that uses NSStream, and I want to add security. I tried to apply the documentation on the subject. I added the following lines to my working networking code: ``` [input setValue:NSStreamSocketSecurityLevelNegotiatedSSL forKey:NSStreamSocketSecurityLevelKey]; [output setValue:NSStreamSocketSecurityLevelNegotiatedSSL forKey:NSStreamSocketSecurityLevelKey]; ``` The initialization code is: ``` -(Connection*) initWithInput:(NSInputStream*) input Output:(NSOutputStream*) output Delegate: (id <ConnectionDelegate>) delegate{ self = [super init]; if (self) { a_delegate=delegate; //set security [input setValue:NSStreamSocketSecurityLevelNegotiatedSSL forKey:NSStreamSocketSecurityLevelKey]; [output setValue:NSStreamSocketSecurityLevelNegotiatedSSL forKey:NSStreamSocketSecurityLevelKey]; a_input=input; a_output=output; //Set delegate to self [a_input setDelegate:self]; [a_output setDelegate:self]; //Schedule in run loop [a_input scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; [a_output scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; //open streams [a_input open]; [a_output open]; } return self; } ``` But when my Connection object is initialized, I get an error message and the networking doesn't work: ``` [<__NSCFInputStream 0x60800028e970> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key kCFStreamPropertySocketSecurityLevel. ``` Is there anything I am doing wrong?