[GreenKeys] Two-tape TTY for crypto

Tue Oct 13 09:33:38 EDT 2020

Dave 

The others covered most of the topic for the PYTHON system. 

I used one for about 18 months while I was in the Navy. It consisted of two 
Model 14 TDs, one of which basically had no controls other than a 'tight tape 
switch. It was 'pulsed' by the main system when the device was in either 
ENCRYPT or DECRYPT, with something or someone making the 'ordinary' 
TD operate. It was interchangeable with the other 14 TDs in the radio room. 

This special TD had a much different serializing plate under the cover. The 
regular TDs had a single copper 'ring' interrupted in several places to represent 
the various parts of an RTTY character. The special TD had this second ring 
to do the 'logic math' to combine the various 'bits' of a character to form the 
'processed' character bit, etc. 

This second ring did not 'do the math', but was part of the system that did. 
The center ring was 'common', and I think that the outer ring was the 'normal' 
one similar or identical to the other TD. The center ring was involved in the 
code/decode function somehow. 

- - - - 

There was a five character 'key indicator' that we watched for. We had only one 
of them in the crypto area. These were spooled on red plastic reels, quite similar 
to 16mm film reels, about 6 or 7 inches in diameter. There was a 'spindle' that 
held the spool to feed this tape into the 'irregular' TD. Each segment was probably 
1000 characters long and there was a 'master number' for the large spools, and each 
one had a number every so many characters with a black line across the tape at 
position "Ø" This was the start point for decoding things. 

The incoming tape had a 'header' with some address info, a Date Time Group 
and date, and somewhere after that were two blank characters. The next character 
was position "Ø" for that. Once both tapes were in place the "GO" button (forgot 
the real name of it!) could be pushed and the two TDs would start moving and as 
has been said several times there was some internal relay logic that took the 'bits' 
and combined them to decide whether that particular location was a Mark or a SPACE 
or a 1 or a Ø, etc. 

As long as the 'random tape' was indeed random, the text would be quite safe. In 
the late 50s and into the early 60s, there were not too many computers fast enough to 
determine the 'randomness' of a code tape, so things were considered safe enough for 
Top Secret items. 

On the few occasions we discovered that a message being decoded was Top Secret, 
the system was stopped and anyone not cleared for T/S had to leave the area. If no 
one was so cleared, a Comm Officer was summoned to complete the decoding. Much 
the same for the KL-47 system in another room. I was also cleared for that equipment, 
but when we were on a WesPac cruise, I had few duties that required me to enter that 
space. In the states, I stood watches in the Main Communications room and when a 
message came in for that system, I would go into the Crypto Center and decode it. 
Again, if the opening phrase was "Top Secret", the system was stopped and someone 
with the proper clearance would be summoned. 

- - - - 

The transition that occurred to make the classification the first word/words happened 
when I was still in the Navy. Evidently, someone, somewhere sent out a classified 
document 'in the clear' which caused 'heartburn' all over the world! So a decision was 
made to prevent this from happening again. The word went out that for any message 
going out on Fleet Broadcasts, the first word of it had to be the classification: 

//UNCLASS// //CONFIDENTIAL// //SECRET// //TOP SECRET// If there 
were more classifications, I never heard about them. Probably just as well! 

Then there were the 'priorities' of Fleet Broadcast traffic: 

Deferred 
Routine 
Priority 
Operational Immediate 
Emergency 
FLASH 
(I think I have these in the right order) 

- - - - 

It was a most interesting time of my life. those two-plus years in Navy communications. 
covering voice, Morse, Teleprinter for the in and out things, and then the various types of encoding/decoding were just 'icing on the cake'! 

Hope my descriptions are not too complicated. That is the way I seem to remember 
things from back then. 

73, 

Ralph - W8ROI 

- - - - - - - - 

From: "Dave Horsfall" <dave at horsfall.org> 
To: "Greenkeys" <greenkeys at mailman.qth.net> 
Sent: Monday, October 12, 2020 3:05:41 PM 
Subject: [GreenKeys] Two-tape TTY for crypto 

I've been reading a bit of crypto stuff lately (one of my hobbies), and 
something caught my eye; apparently Teletype made a box that took two 
tapes: one was the plain/cipher text, and the other was the key, and the 
two were combined with no-carry addition on the individual bits. 

Anyone know any more about this? 

-- Dave VK2KFU 
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