So many responses in this thread I apologize if I am repeating.
There are three levels of classification which are based on the IMPORTANCE or IMPACT disclosure of the information may have. I have forgotten the exact definitions in the past forty some years but Top Secret information is vital info that if revealed could presumably cause the greatest harm to the nation. Secret and Confidential are the others in descending order.
Certain types of information is much more carefully monitored and controlled. Among these are CRYPTO which word applies to all information related to codes, coding, coding methods, coding equipment. The reason this information is so designated is because if CRYPTO is compromised more than one secret or one type of secret may be compromised. Many messages can be compromised. I was a Crypto systems technician and normally didn’t deal with the actual information sent but that meant I had to had the clearances to deal with information to be found wherever the equipment I might access would be found.
Codewords are many. SCI means the information is restricted, as all information is, on a need to know basis, with the proviso that the particular codeword indicates something more is involved. For example, some codewords, Ultra has been mentioned, is designed to convey both the source of the information so that the source can be protected – and the material as well so that it is not released to anyone not authorize to receive Ultra information. And since the existence of the Ultra information would compromise the whole Ultra (Enigma decoding) program that word itself was probably classified. Finally by knowing that the information is ULTRA the user may have a better handle on how reliable the information is. Intelligence that you cannot depend on is useless. So many codewords are used to protect a source and to allow evaluation of the information from that source.
I had access to SCI information of several sorts. When i was “read into” one program – explained to me the program and given access to it and told of the special restrictions on the information – I was handed a small folded card and opened it to read the Code Word. It was never stated out loud. It was itself a secret that could not be divulged beyond another person who had access to that information. I think it is in fact in the common domain now but still I won’t say what it was/is just in case.
And more. Special markings are used to indicate information or physical security that gets extra protection. For example I worked in nuclear missile silos and command posts at one point, and had to be cleared under the Human Reliability and Personnel Reliability Programs which meant among other things my medical records had special markings to indicate to medical personnel they were obliged to report anything that suggested I was no longer reliable. These marking don’t apply to the information but to the program as a whole but in order to go to the areas restricted I needed security clearances, etc.
Because of some of the SCI I had access to I was not permitted for example to take commercial aircraft that went over a Communist Nation nor travel to certain other areas on leave. I was transferred to Turkey at one point but I was not allowed to take the usual air route to Istanbul because it went over Yugoslavia. I had to fly to Rome first and take a direct flight to Istanbul.
Now all the equipment I worked on is no longer secret and there are web pages describing it and photos of the equipment, etc. all legally released there’s a museum in fact and you can see it online. So I can tell you that when the Pueblo was seized the Crypto equipment was compromised (seized) and after a few years the NSA decided that the KG-13 system needed to be physically changed to ensure its security. Without the codes themselves in theory the equipment was not enough to compromise the info transmitted but if you know enough it might be possible to break the codes.
I actually surmise that they knew or believed the codes had been broken on an ongoing basis which is not supposed to be possible. And in fact they were right, many of our codes were compromised and the Soviets could read all of our traffic.
I tell this story in part to show how many different security classifications and programs work and interact.
So at any rate on one particular day I had to take a helicopter to move between two missile alternate command posts at silos to modify the KG-13s at those sites as result of the concern they had been compromised, A new circuit board was installed to change the way in which the system encoded and decoded information. That change had to be made at a specific time for each post and we couldn’t drive between them in time. There were not enough of us to send two teams out.
That was Top Secret Crypto information at the time and I had to explain to the colonel who was pissed that HE couldn’t get a chopper that I couldn’t tell him why I did get one. Nor could I tell the missile crews what we were going to do, even though they had access to the machines and codes. And I had to take another tech with me because the machines are located in NO LONE ZONES which is an area where no one can go without a companion because it relates to the launch of nuclear weapons. I had clearance for that too.
The irony of it all is that John Walker of the US Navy was giving ever bit of Crypto he could get his hands on to the Soviets and the surely had the new circuit board design not long after – and possibly before – I did that installation. And in fact he compromised mostly Navy codes with that but indeed he may have compromised pretty much everything sent on the major systems KW26, KW7, KY3, KG13 and others.
Which is why the spy game makes most of this meaningless.
BUT it also lets me tell you that for the SCI information different codes were used for any circuit that carried that info and Walker probably didn’t have access to that program so he probably could not give away the Crypto codes for those particular circuits. So the SCI may not have been compromised. At least, not that way.
