[GreenKeys] overprinting

[Chris Elmquist]

This was definitely a common technique with timesharing systems, often
accessed with M33's, to facilitate obscuring a password during login.

You'd see your password as you typed it but when you hit return, the
remote system would then overtype with X, M, Z, *, etc. to black out the
password text.  Each line of those obscuring characters was terminated
by only <CR> so that it would print it all on top of what it had just
printed earlier.

If the connection to the remote system was full-duplex, then they would
typically not echo back during password entry so nothing would print--
although I certainly remember encountering both-- where the password you
typed was not echo'd and it also overprinted when you were done entering.
This was obviously because they didn't know if the remote terminal was
doing local echo or not.

Chris N0JCF


On Friday (10/19/2012 at 02:08AM -0400), WA5CAB at cs.com wrote:
> Provisionally, yes.  And no.  
> 
> If your machine is a 14/15/19/20/26/28 and you are printing what you are 
> sending so that you can see what is being printed, you can send a CR, SPACE 
> down to where you want to overprint, and print something (an X, perhaps) over 
> each character that you wish to overprint.  Then space down to where you 
> were and continue.  If the receiving machine is also a page printer, it will do 
> exactly the same thing.  
> 
> However, if the receiving machine is a reperf punching tape, it will not 
> work.  But if the receiving station prints from the tape, that will work as 
> the printer will do the same thing that your monitor machine did.
> 
> If you are punching a tape, you can do the same thing but you will only get 
> it right if you are also printing what you are punching.
> 
> There is no backspace on any of these machines that I ever heard of.  At 
> least not the military ones.
> 
> If you are using a rubber band and door spring machine, then I don't know.
> 
> In a message dated 10/19/2012 00:49:37 AM Central Daylight Time, 
> legalize at xmission.com writes: 
> > OK, please forgive my ignorance if this seems a dumb question.
> > 
> > Can you overprint with a teletype by sending CR (but no LF) or using
> > backspace?
> > -- 
> 
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480

> ______________________________________________________________
> GreenKeys mailing list
> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:GreenKeys at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html


-- 
Chris Elmquist