[GreenKeys] ASR on Ebay

[David Burns]

I think George has gotten to the bottom of the AUTODIN dual-reader 28ASR.

The second tape reader is for the key-encryption tape that must step 
simultaneously with the plain-text tape carrying the message to be 
encoded or decoded.

The notch in the side of the tape (punched into the incoming message) is 
probably designed to mark the start or end of the message to be 
processed.  The keytape (containing a uniformly scrambled set of 5-unit 
codes with no particular meaning) and the outgoing message tape would 
each be inserted into their corresponding readers with their notches 
aligned, and the transmission started.  The tapes step together, and the 
crypto-unit combines the two codes (almost certainly using some 
exclusive-OR operation coupled with a patch-panel/card-reader that 
allows changing the scheme) into a single stream that is put on the 
outgoing circuit.

So this ASR was for secret-message transmission, but now available on 
eBay stripped of its ability to 'be secret'.  Cost the government 
thousands, yours for $600!