A few weeks ago, additional parts of the “A History of U.S. Communications Security” books from the NSA were declassified. A little intrigued, I decided to read the second volume that was originally published in 1981 under the SECRET classification. I wondered what we could learn, in 2015, from the dated document.

Note: For legibility reasons I transcripted the original notes. Italic was in original text. I’m highlighted segments in bold and added links for important references.


The main argument for COMSEC for military operations that the author is bringing forward is that COMSEC is a crucial element to maintain the “surprise” element of operations.

Operations Security (OPSEC) is a discipline designed fundamentally to attain and maintain surprise, particularly in military operations.

COMSEC is a key ingredient of OPSEC - it may help achieve surprise, nor with the correlative assertion that fewer and fewer major operations can be planned and executed these days without a large amount of supporting communications to coordinate, command and control them, nor even with the assertion that,without security for those communications, surprise is unlikely

On Threat Modeling

No COMSEC tool (messaging app, radio, … ) is a silver bullet. Ideally, it will minimize “what could go wrong”, but there will always be ways of using it in an unsafe manner. Authentication is one of the hardest challenges that is yet to solve. Asking people to manually verify fingerprints comes at a huge usability trade-off. The following segment highlights the important idea of first trying to find technical solutions to the problem before going after procedural solutions. Nobody likes manual key verification, but no technical solution has currently been found to satisfy the same level of security without adding that procedural step.

In olden times, most of our programs, whether in equipment development, TEMPEST, or security procedures were driven largely by our view of COMSEC weaknesses - our vulnerabilities - more or less independent of judgements made on the ability of an opponent to exploit them. We assumed hostile SIGINT to be at least as good as ours, and used that as a baseline on what might happen to us. If we perceived a weakness, we would first try for a technical solution - like new crypto-equipment. If the state of the art did not permit such a solution, or could do so only at horrendous expense, we’d look for procedural solutions and, those failing, would leave the problem alone.

So our priorities were developed more or less in the abstract, in the sense that they related more to what we were able to do technologically or procedurally than the probabilities that a given weakness would be exploited in a given operating environment. In short, we did not do much differentiation between vulnerabilities which were usually fairly easy to discover and threats (which were more difficult to prove) - where threats are are fairly rigorously defined to mean demonstrated hostile capabilities, intentions, and/or successes against U.S. communications. The accusations of overkill touched on earlier in part stemmed from that approach.

The thrust towards gearing our countermeasures to threat rather than theoretical vulnerability was healthy, and driven by a recognition that our resources were both finite and, for the foreseeable future, inadequate to fix everything. In fact, one of the reactions of an outside analyst to our earlier approach was, “These nuts want to secure the world”. Some still think so.

If your crypto doesn’t work, nobody will use it

During the Vietnam war, the encryption was reducing the transmission range and introducing unacceptable delays in radio communications. Some pilots got frustrated about it and fell back to plaintext communications. A commander had to threaten his pilots to ground them to get them to use NESTOR, the encryption system that was implemented on top of radio communications.

Finally, our own engineers sent to Vietnam reported back: “Sorry about that, S2; the system reduces range - typically by 10% or more.” And it, in fact, did. It turned out that NESTOR did not affect range only if the associated radio was perfectly tuned, “peaked,” matched to the NESTOR equipment (as we naturally did here at home). In the field, maintenance personnel were neither trained nor equipped for such refinement - the test instrumentation simply did not exist there, and we had not anticipated those real world conditions when we sent it out.

In tactical air, it was claimed that the delay - up to 3/5 of a second of required wait between pushing to talk and ability to communicate - was intolerable when air-to-air warnings among pilots had to be instantaneous. A survey showed, by the away, that most pilots judged this time to be on the order of three seconds; so, in fact, the wait must have seemed interminable when one wanted to say “Bandit at two o’clock.”

Most US SIGINT assets in Vietnam used NESTOR heavily and successfully almost from the outset. Towards the end of the war, so did most in-country Naval forces, particularly airborne assets. In the SIGINT user’s case, it was because they were already equipped when they got in country; had used it previously, knew, accepted or circumvented its peculiarities, and, of course, because they believed their traffic required protection. In the Navy case, it was the result of Draconian measures by the Commander, Naval Forces, Vietnam (COMNAVFORV). That Admiral happened to be a COMSEC believer; so he told his pilots that if they didn’t use the equipment, he’d ground them. Some didn’t and he did. There is, I understand, no comparable trauma for a fighter pilot.

Dealing with compromise

Every time I read a headline that reads “X is broken” where X is a messaging app, an anonymity program or other, I fear that people might just give up on using encryption thinking that everything is broken anyways and thus it’s useless to take any defensive measures.

Unless there is a good alternative, it’s really deceptive to just blame the tool that offers the best protection.

A caveat: While nothing gets a user’s attention like documented proof that communications he thinks are sensitive are being read by an opponent, several things should be borne in mind before telling him about it. Foremost is the fragility of the source of the information (the “proof”) you have. Secondly, it is worse than useless to go out and impress a user with a problem unless you have a realistic solution in hand. No matter how dramatic the evidence of threat, if we simply go out and say, “Stop using your black telephone”, it’s likely to be effective for about two weeks. Don’t jeopardize a good source for that kind of payoff.

Finally, the results of our own monitoring and analysis of communications,at best, prove vulnerability, not threat, are often remarkably ineffective. Nothing brought this home more persuasively than the Vietnam experience. Monitoring elements of all four Services demonstrated the vulnerability of tactical voice communications again and again. This did not show that the NVA or VC could do it. It was first argued that they weren’t engaged in COMINT at all. Next, that even if they were able to intercept us, they couldn’t understand us, especially given our arcane tactical communications jargon. Third, even given interception and comprehension, they could not react in time to use the information.

It took years to dispel those notions with series of proofs in the form of captured documents, results of prisoner and defector interrogations, some US COMINT and, finally, the capture of an entire enemy COMINT unit: radios, intercept operators, linguists, political cadre and all. Their captured logs showed transcriptions of thousands of US tactical voice communications with evidence that their operators were able to break our troops’ home-made point-of-origin, thrust line, and shackle codes in real time. The interrogations confirmed their use of tip-off networks (by wire line or courier) to warn their commanders of what we were about to do - where, when, and with what force.


NSA thought that declassifying crypto algorithms would lead to having more integrated options for communication devices. Sadly, a lot of privacy tools are still a hack on top of a protocol (SMS, Jabber, Email …) and not well integrated. As long as crypto is the topmost layer of the OSI model, we’re going to lose users.

The two major reasons for declassification were the “inhibition of use” argument, and the vision of full integration of COMSEC circuitry into radios of the future - full integration being defined as inseparable and shared radio and crypto-circuitry. In that configuration, our COMSEC tail would be wagging the communications system dog with the controls classification denotes - how would such equipments be shipped, stored, and particularly, how would they be maintained? “Integration” has thus far not turned out to be the wave of the future. COMSEC modules will by and large be separable from their associated radios because the designers found it more efficient to do it that way. […]

Offence is easy

As the rest of the security community, NSA is good at offence, but has no clue how to secure a system.

It seems to me that NSA does not yet have much expertise in computer security. Rather, we are expert in computer insecurity. We do much better in finding security vulnerabilities in any computer complex than in proposing security architecture for them. Somehow the attack seems more challenging (fun) than the defence, and this seems true in the general business of crypto system design as well. A spin-off of this syndrome manifests itself when a security modification is needed for an existing crypto-equipment. In my experience, most design engineers would much rather attack a brand new problem - meet a new and difficult requirement - starting from scratch, pushing the electronic state of the art, exercising opportunities for innovations, and so on than go through the drudgery of a mere “fix” accepting the constraints of configuration and technology in some pre-existing piece of hardware.

The Cost of Transparency

Soviet’s were apparently not revealing any information about their COMSEC programs. I’m not sure we would know much about NSA’s without whistleblowers.

NSA spends tens of millions of dollars and tens of thousands of man-hours trying to discover what Soviet COMSEC is like. Despite all-source research dating back to more than 30 years, the incidence of any unclassified statements by the Soviets on any aspect of their COMSEC program is so trivial as to be virtually non-existent. In other words, the Soviets protect (classify) all information about their cryptography and associated communications security measures. The effect of this stone wall has been either to greatly delay U.S. ability to exploit some Soviet communications or frustrate it altogether. Viewed as an element of economic warfare, we are losing hands down as we expend enormous resources to acquire the same kind of information from the Soviets that we give them free - i.e., without classification. Clearly, the Soviet’s classification program costs them something, just as ours costs us. But, they have a cost advantage because they still operate in an essentially closed society with a well-established security infrastructure and with many of their officials already well attuned psychologically to the concept of secrecy.

Value of crypto-analytic information

For NSA, the best way for breaking a crypto system is to break the math, not the implementation. I assume this argument is based on the fact that a passive attack is superior to an active one.

The optimum attack on any crypto system (if you can hack it) is cryptanalytic - you need only operate on cipher text; your risk is low or non-existent unless you have to position yourself dangerously to perform the interception. You don’t need to steal keys or penetrate cryptocenters or subvert people and, if you succeed, the return on investment is likely to be rich - all the secrets committed to the cryptosystem in question. The one essential pre-requisite to such attack is knowledge of the cryptologic - which may have been the reason why the Soviets were (reportedly) willing to offer $50, 000 for PARKHILL several years ago.

The “SIGINT” argument for protecting our cryptologics is well known - the COMSEC arguments much less so, despite their reiteration for some decades: - With the exception of true one-time systems, none of our logics is theoretically and provably immune to cryptanalysis - the “approved” ones have simply been shown to adequately resist whatever kinds of crypto-mathematical attacks we, with our finite resources and brains, have been able to think up. We are by no means certain that the Soviet equivalent of A Group can do no better. But no attack is likely to be successful - and certainly cannot be optimised - without preliminary diagnostics - discovery of how it works. - Systems which have no known cryptanalytic vulnerabilities may still be exploited if, and usually only if, their keying materials have been acquired by the opposition or if their TEMPEST characteristics permit it. In either of these contingencies, however, the logic, the machine itself, or both may be required for exploitation to be successful.

Because the thrust for unclassified when unkeyed equipments is lying fallow at the moment, all of the above may seem like beating a dead horse as far as our mainline equipment are concerned. But the matter will assuredly rise again.

Public Cryptography

The COMSEC guide also talks about the rise of non-governmental encryption and more specifically the discovery of “RSA” by GCHQ a few years before it was publicly discovered.

While commercial equipment has been around for many decades, their quantity and variety was relatively small. Most were manufactured overseas - particularly in Switzerland, and no huge market existed for them after World War II because many Governments (like our own) began increasingly to use systems exclusively of their own design and under their own control. Similarly, the amount of published literature on cryptography, and particularly on sophisticated cryptanalytic ideas was sparse. In the U.S., the Government (specifically, NSA) enjoyed a near-monopoly on the subject by the early ’50’s. That persisted until about 1970, when a dramatic change occurred. A handful of U.S. companies interested in computers, in communications, or in electronics began to perceive a market for electronic crypto-equipments. A few other American companies began building crypto-equipment in competition with the Swiss and others in Europe, supplying devices to some Governments in Africa, South America, and the Middle East and to a few major corporations - notably some oil companies seeking to protect vital industrial secrets. At about the same time, the question of computer security, which had been on the back burner since the late 50’s, began to get a great deal of attention from computer manufacturers themselves and from some of their customers. Computer fraud had become more common, and its impact, particularly on the banking world, became significant.

One of the interesting outgrowths of the burgeoning interest in cryptography in the private sector was the “invention” of a concept called “Public Key Cryptography” (PKC). All conventional cryptography requires the pre-positioning of shared keys with each communicant. The logistics for the manufacturing and delivery of those keys keeps S3 in business and forces uses to maintain a large secure crypto-distribution system. (Remote keying eases but does not eliminate the problem) The thought was, cryptography would be revolutionized if a system could be devised in which people could communicate securely without prior exchange of keys. The main idea that came forward was an effort to capitalize on the fact that some mathematical functions are easy to carry out in one “direction,” but difficult or impossible to reverse. A classic example of these so-called one-way functions is the phenomenon that it is not hard to multiply two very large prime numbers together, but given only their product, no elegant way has been put forward for determining what the two original numbers were. So the original numbers could be considered to be part of the one man’s secret “key:” their product could be published; an encryption algorithm could be specified operating on that product which could not be efficiently decrypted without knowledge of the “key”; and all messages addressed to that person would be encrypted by that algorithm. By coincidence, the identical idea had been put forward by one of our British colleagues five years earlier, and we and they had been studying it ever since. We called it non-secret encryption (NSE) and were trying to solve the same problem of key distribution. We treated our work on it as SECRET and still do. We did not leap to its adoption for a variety of a reason. Foremost, we were uncertain of its security potential. The fact that mathematicians had not yet found a way to factor large numbers did not mean that there was no way. It was an interesting mathematical puzzle, first put forward centuries ago, but no great incentives for its solution beyond the satisfaction of intellectual curiosity, no perceived commercial applications, and so on. So there was no e evidence of a great many brains having worked on the problem over the year; nor did we go all out against it because, apart from theoretical doubts, there were other drawbacks. The most obvious - although perhaps not the most important - was the fact that the encrypted himself could never decrypt his own message - he would be using the crypto system of the recipient who was the only one holding the secret decrypting key - he would have no means to verify its accuracy or correct an error. More or less elaborate protocols involve hand-shaking between the communications were put forward to get around this difficulty - usually entailing the receiver having to re-encrypt the received message in the sender’s key and asking if it was right. A clumsy business. Next, each user would have to keep his primes absolutely secret, forcing on each some of the secure storage and control problems inherent within conventional schemes. Known (or unknown) loss would compromise all of his previously received messages. To get around that, relatively frequent change would be necessary. This would move him towards the conventions of keying material supersession; generation and selection of suitable primes and their products, and their republication to all potential correspondents.

Embassies and SIGINT

Soviets were suspected of intercepting communications in the Washington area and elsewhere in the United States. Therefore, the NSA was pressured by the Government to disclose and share more about their knowledge about cryptography.

Soviet SIGINT got out of control and weakened telecom infrastructure was so vulnerable that the Vice-President Rockefeller said: “If you don’t want it known, don’t use the phone”. Take that as an opsec advice.

Another major factor arose bringing great pressure on NSA to let some of our cats out of the bag. This was the matter of Soviet interception of communications in the Washington area and elsewhere in the United States. By 1966, we were pretty sure that they were doing this work from their Embassy on 16th Street and perhaps from other facilities as well - but we had no clear idea of its scope, its targets, possible successes, not of the value of the information they might be collecting.

This paragraph is followed by a large redacted area to this day. And then continues

By the early 70’s, evidence had accrued confirming the Soviet intercept effort, and it was shown to be large and efficient. [REDACTED] characterised their intercept effort from their Washington Embassy as the single most valuable covert SIGINT activity in their arsenal. The vulnerable communications obviously extended beyond those of our traditional military and diplomatic customers. Privacy for individual citizens could be violated; technological information communicated by Defense contractors could be compromised, and information useful in economic warfare could be obtained. The threat became public and explicit in the waning days of the Ford Administration with Vice-President Rockefeller announcing in a press conference that “If you don’t want it known, don’t use the phone”. Later on, in a press conference, President Carter acknowledged the existence of the problems, characterized the Soviets’ efforts as passive, noted that all “his” communications were secured and did not appear too upset. Senator Moynihan, however, expressed outrage, wanted to jam the Russians, expel them, or something because of their outrageous invasion of US citizens’ privacy.

The reason why the president probably wasn’t that outraged compared to the Senator is probably because he knew the US embassies were doing the same …

By this time, we had bitten the bullet, deciding to seek a generic COMSEC solution. This was a decision of enormous consequence for us. The notion of injecting Communications Security into the commercial world in a big way was unprecedented, with serious policy, political, and technical implications for all involved. Principal players became ourselves, the telephone companies, the White House, DCA, the now defunct Office of Telecommunications Policy in OMB, FCC and, ultimately many users of the commercial telephone system.

The project was (and is) called HAMPER. At the outset, it had three main thrusts: a greatly expanded program to move “sensitive” circuits to cable in Washington, NYC and San Francisco where major Intercept activities were now known to exist; a program to bulk encrypt some of the tower-to-tower microwave links in their entirety, re-inforced by end-to-end encryption for some particularly critical lines; and the definition of “Protected Communications Zones” to circumscribe those areas - e.g., Washington and its environs - from which microwave interception would be relatively safe and easy. It took several years of concerted effort simply to sort out how communications were routed through the enormously complex telephone system.

With that deployment, cryptography became increasingly prominent in the private sector. Raising some concerns for NSA.

The doctrinal problems were large and intractable because they involved the provision of cryptography in unclassified environments where many of our traditional physical security measures were thought to be inapplicable. How would the crypto-equipments be protected? How to protect the keys? How do you effect key distribution with no secure delivery infrastructure such as we enjoy in the Government COMSEC world? Problems of this kind let to campaign to use the DES - the only unclassified Government-approved crypto system available, thus solving the physical security problem insofar as the crypto-equipment itself was concerned. The root difficulty with this proposal from the security analysts’ viewpoint lay in the fact that the DES algorithm was originally designed and endorsed exclusively for the protection of unclassified data, fundamentally to insure privacy, and without a SIGINT adversary with the power of the Soviet Union having been postulated as a likely attacker. Accordingly, the system was not designed to meet our high grade standards and were not interested in educating the world at large in the best we can do.

This is really interesting. It’s another example of intelligence agencies struggling to reconcile their Information Assurance and SIGINT sides. They thus admit not protecting citizens and US companies at risk of Soviet spying with the only goal of being still able to spy more on the Soviet.

Nonetheless, the system is very strong; has stood up to our continuing analysis, and we still see no solution to it short of a brute force exhaustion of all its 2^56 variables. It is good enough, in fact, to have caused our Director to endorse it not only for its original computer privacy purposes, but for selected classified traffic as well. Cynics, however, still ask “Are we breaking it?” The answer is no. But could we? The answer is “I don’t know; if I did I wouldn’t tell you” And there’s a good reason for this diffidence. A “No” answer sets an upper limit on our analytic power. A “Yes” answer, a lower limit. Both of those limits are important secrets because of the insights the information would provide to opponents on the security of their own systems.

NSA won’t reveal if they can break something. We all knew that this was happening but interesting to read an internal document confirming that practice.

the Hamper program faltered because of uncertainties on who was charged with, responsible for, authorized to, or capable of moving forward. Big money was involved and we didn’t know who should budget for it. Should the common carriers pay for it themselves, or its customers? Or the government? It is, after all, a security service that most may not want or perceive a need for.

By and large, most people in both the COMSEC and SIGINT organizations in NSA believe that we can accomplish our missions more effectively in considerable secrecy because it helps us to conceal our strengths and weaknesses and to achieve technological surprise. DoC [Department of Commerce], on the other hand, is in business, in part, to encourage private enterprise, to maximize commercial markets at home and abroad, and to exploit the products of our own Industry for use in Government rather than having the Government compete with Industry and this does not exclude cryptography.

Academic Freedom vs National Security

In any event, production and marketing of equipment by U.S. commercial vendors is not our biggest problem with public cryptography because there are various Government controls on such equipment - particularly, export controls - and Industry itself is usually disinterested in publishing the cryptanalytic aspects of their research in any detail. The central issue that continues to fester is encapsulated in the phrase: “Academic Freedom versus National Security”.

Our Director has made a number of overtures to various academic forums and individuals in an effort to de-fuse this issue, but has stuck to his guns with the statement that unrestrained academic research and publication of results can adversely affect National Security. While a few academicians have been sympathetic, the more usual reaction - at least that reaching the press - has been negative.

The principal reason that there is an NSA consensus that unrestrained academic work has the potential for harm to our mission is because, if first-case U.S. mathematicians, computer scientists, and engineers begin to probe deeply into cryptology, and especially into cryptanalytics, they are likely to educate U.S. SIGINT target countries who may react with improved COMSEC. Less likely, but possible, is their potential for discovering and publishing analytic techniques that might put some U.S. crypto systems in jeopardy.

The academicians’ arguments focus on absolute freedom to research and publish why they please, a rejection of any stifling of intellectual pursuit, and concerns for the chilling effect of any requests for restraint. Their views are bolstered by the real difficulty of differentiating various kinds of mathematical research from “crypto-mathematics” - notably in the burgeoning mathematical field of Computational Complexity, often seeking solutions to difficult computational problems not unlike those posed by good cryptosystems.

As a practical matter, Government “leverage,” if any, is rather limited. We have made some half-heated attempt to draw an analogy between our concerns for cryptology with those for private research and development in the nuclear weapons field which led to the Atomic Energy Act that does - at least in theory - constrain open work in that field. But there is no comparable public perception of clear and present danger in the case of cryptology and, despite the “law,” academicians have sanctioned research revelatory of atomic secrets including publications on how to build an atomic bomb.

That’s where it gets interesting.

Another wedge, which as yet has not been driven with an appreciable force, is the fact that - overwhelmingly - the money underwriting serious unclassified academic research in cryptography comes from the Government itself. Among them are the National Science Foundation (NSF), the Office of Naval Research (ONR) and the Defense Advanced Research Projects Agency (DARPA). NSA supplies a little itself. The wedge is blunted because Government officials administering grants from most of these institutions have been drawn largely from the academic community who believe strongly in the value of research performed outside Government, and are sympathetic to concerns about abridgement of Academic Freedom.

In following paragraphs, the author explains that NSA has tried to make more bridges with academia and convince them to be “reasonable”.

Burn after reading

NSA masters pyrotechnic techniques to burn crypto equipment when it is at risk of compromise. After previous failures of keeping crypto-equipment safe from foreign reverse-engineering, they got a big success during the 1979 Iranian revolution where they burned all of the US equipment that was at risk of being compromised.

The most successful use of pyrotechnics (thermate slabs, thermite grenades, and sodium nitrate barrels) in Tehran occurred at the major Army Communications Center there. It had a number of crypto-equipments, but also served as a depot for pyrotechnic materials for the whole area. They piled all of their classified crypto material in a shed; covered them with their pyrotechnical material (some 300 devices), lit off the whole enchilada, and took off. The result was probably the largest single conflagration during the entire revolution. Observers reported seeing flames shooting hundreds of feet into the air from posts several miles away. The building was, of course, consumed and we assume only a slag pile remains. […]

There are many more topics covered that I have decided to leave out of this summary. If this sounded interesting, you might want to take a look in the COMSEC guide for yourself!