Computing Applications Practice

Who Must You Trust?

You must have some trust if you want to get anything done.
  1. Introduction
  2. Heartbleed
  3. Systems Administrators
  4. Who Must You Trust?
  5. How Much Do You Need to Trust?
  6. Who Is Everybody Else Trusting?
  7. How Are Services Evaluated for Security?
  8. Thinking About the Bad Cases First
  9. What Can You Do?
  10. Conclusion
  11. Acknowledgments
  12. References
  13. Author
Who Must You Trust? illustration

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In his novel The Diamond Age,5 Neal Stephenson describes a constructed society (called a phyle) based on extreme trust in one’s fellow members. One of the membership requirements is that, from time to time, each member is called upon to undertake tasks to reinforce that trust. For example, a phyle member might be told to go to a particular location at the top of a cliff at a specific time, where he will find bungee cords with ankle harnesses attached. The other ends of the cords trail off into the bushes. At the appointed time he is to fasten the harnesses to his ankles and jump off the cliff. He has to trust the unseen fellow phyle member who was assigned the job of securing the other end of the bungee to a stout tree actually did his job; otherwise, he will plummet to his death. A third member secretly watches to make sure the first two do not communicate in any way, relying only on trust to keep tragedy at bay.

Whom you trust, what you trust them with, and how much you trust them are at the center of the Internet today, as well as every other aspect of your technological life.

Here is an experiment to try. Take walks in various mixed-use neighborhoods with a variety of residences and businesses. Walk in the daytime, before and after lunch. Walk in the nighttime, at the height of the evening activities. Walk late at night, after most things have shut down. With each outing, put yourself in a security mind-set—which is to say, look with the eyes of a thief and notice what you see.

During the day, for example, at busy sidewalk cafes, do people reserve outdoor tables by placing their possessions on the table and then going inside to order? Do they use their grocery bags for this? Their car and house keys? Their wallets?

Late at night, are those same tables and chairs stacked outside or inside? Are they chained together? Are the chains lightweight or substantial?

Do the neghborhood home have porch furniture or lawn tools visible from the street? Are they locked up? Do you see bars on the windows of the homes? Are the family cars parked outside? Do they have steering-wheel locks?

Do postal workers or delivery services leave packages unattended by the front doors of houses? Are bundles of newspapers and magazines left in front of newsstands before they open?

These observations, and many more, are flags for the implicit levels of trust that people have in their neighbors and neighborhoods. The people themselves may not even think of these things. They may leave things on their porches, perhaps accidentally, and nothing bad happens, so they do not worry if it happens again. After a while, it becomes something they do not even notice they do.

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In spring 2014, a bug in the open source package OpenSSL became widely known. Known as Heartbleed (, the bug had been present for some time, and may have been known by some, but the full disclosure of the problem in the OpenSSL package came to the public’s attention only recently. OpenSSL had been reviewed by many experts and had been a well-used and trusted part of the Internet ecosystem until that point. As of this writing, there is no evidence suggesting any cause other than a programming error on the part of an OpenSSL contributor.

On the morning before the Heartbleed bug was made public, few people were familiar with OpenSSL and hardly gave the functions it provided a second thought. Those who knew of it often had a strong level of trust in it. By the end of the day, that had all changed. Systems administrators and companies of all sizes were scrambling to contain the problem. In just a few days, this obscure piece of specialized software was at the top of the news cycle, and strangers—sitting in outdoor cafes at tables they had reserved with their house and car keys—were discussing it in the same tones with which they might have discussed other catastrophes.

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Systems Administrators

At the heart of everything that works on the Internet are systems administrators. Sometimes they are skilled experts, sometimes low paid and poorly trained, sometimes volunteers of known or unknown provenance. Often they work long, unappreciated hours fixing problems behind the scenes or ones that are all too visible. They have access to systems that goes beyond that of regular users.

One such systems administrator worked for the National Security Agency. His name is Edward Snowden. You probably know more about him now than you ever expected to know about any sys admin, even if you are one yourself.

Another less familiar name is Terry Childs,3,7 a network administrator for the city of San Francisco, who was arrested in 2008 for refusing to divulge the administrative passwords for the city’s FiberWAN network.

Whatever components or services you choose, consider how they have been tested for trustworthiness.

This network formed the core of many city services. According to reports, Childs, a highly qualified and certified network engineer, was very possessive of the city’s network, having designed and implemented much of it himself—perhaps too possessive, as he became the sole administrator of the network, claiming not to trust his colleagues’ abilities. He allowed himself to be on-call 24/7, year-round, rather than delegate access to those he considered less qualified.

After an argument with a new boss who wanted to audit the network against Childs’ wishes, the city’s CIO demanded that Childs provide the administrative credentials to the FiberWAN. Childs refused, which led to his arrest. His supervisors claimed he was crazy and wanted to damage the network. Childs claimed he did not want to provide sensitive access credentials to unqualified individuals who might damage “his” network.

In 2010, Childs was found guilty of felony network tampering and sentenced to four years in prison and $1.5 million in restitution for the costs the city incurred in regaining control of the network. An appeals court upheld the verdict.

Was Childs a fanatic, holding on too tight for his own good, or a highly responsible network admin who would not allow his network to be mismanaged by people he considered to be incompetent? His case brings up these questions:

  • Could something like this happen at your enterprise? How would you know this problem was developing, before it became a serious problem?
  • What safeguards do you have in place to prevent a single-point concentration of power like this?
  • What would you do if your organization found itself in this situation?

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Who Must You Trust?

Some people dream of going back to nature and living apart from the rest of humanity. They will build their own cabins, grow or raise their own food, and live entirely off infrastructure they have built with their own two hands and a trusty axe. But who made that axe? Even if you can make a hand-chipped flint axe from local materials, it is far from “trusty,” and the amount of wood you can cut with a flint axe pales in comparison to what you can cut with a modern steel axe. So if you go into the woods with a modern axe, can you truly say you are independent of the world?

If you work on the Internet, or provide some service to the Internet, you have a similar problem. You cannot write all of the code if you intend to provide a modern and useful network service. Network stacks, disk drivers, Web servers, schedulers, interrupt handlers, operating systems, compilers, software-development environments, and all the other layers needed to run even a simple Web server have evolved over many years. To reinvent it all from the specifications, without using other people’s code anywhere in the process, is not a task for the fainthearted. More importantly, you could not trust it completely even if you did write it all. You would be forever testing and fixing bugs before you were able to serve a single packet, let alone a simple Web page.

Neither can you build all of the hardware you run that service on. The layers of tools needed to build even a simple transistor are daunting, let alone the layers on top of that needed to build a microprocessor. Nor can you can build your own Internet to host it. You have to trust some of the infrastructure necessary to provide that service. But which pieces?

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How Much Do You Need to Trust?

To determine how far your trust needs to extend, start with an evaluation of your service and the consequences of compromise. Any interesting service will provide some value to its users. Many services provide some value to their providers. What is valuable about your service, and how could that value be compromised?

Once you have a handle on these questions, you can begin to think about the minimum of components and services needed to provide such a service and which components you have to trust.

Writing your own software can be part of this exercise, but consider the bulk of security derived from that is what is known as “security through obscurity.” Attacks will fail because attackers do not understand the code you have built—or so some think. If you choose the path of obscurity as a strategy, you are betting that no one will show interest in attacking your service, that your programmers are better than others at writing obscure code in a novel way, and that even if the code is obscure, it will still be secure enough that someone determined to break through it will be thwarted. History has shown these are not good bets to make.

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Who Is Everybody Else Trusting?

A better approach might be to survey the field to see what others in similar positions are doing. After all, if most of your competitors trust a particular software package to be secure, then you are all in the same situation if it fails. There are variables, of course, because any software, even the best, can be untrustworthy if it is badly installed or configured. Furthermore, your competitors might be mistaken.

A variation on this approach is to find out which software all of your competitors wish they could use. Moving to what they use now could leave you one generation behind by the time you get it operational. On the other hand, moving to one generation ahead could leave you open to yet-undetected flaws. The skill is in choosing wisely.

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How Are Services Evaluated for Security?

Whatever components or services you choose, consider how they have been tested for trustworthiness. Consider these principles attributed to Auguste Kerckhoffs, a Dutch linguist and cryptographer, in the 19th century:

  • The system should be, if not theoretically unbreakable, then unbreakable in practice.
  • The design of a system should not require secrecy, and compromise of the system design should not inconvenience the correspondents.

Kerckhoffs was speaking of cipher design in cryptosystems, but his two principles listed here can be applied to many security issues.

When considering components for your enterprise, you should ask if they live up to Kerckhoffs’ principles. If they seem to, who says that they do? This is one of the strongest cases for open-source software. When done properly, the quality and security of open-source code can rival that of proprietary code.2

For services you wish to subscribe to, consider how often and how thoroughly they are audited, and who conducts the audit. Do the service providers publish the results? Do they allow prospective customers to see the results? Do the results show their flaws and describe how they were fixed or remediated, or do they just give an overall thumbs-up?

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Thinking About the Bad Cases First

The legendary Fred Brooks, he of The Mythical Man Month,1 famously said: “All programmers are optimists.” Brooks meant this in terms of the tendency of programmers to think they can complete a project faster than it will actually take them to do so. But as Communications‘ own Kode Vicious is wont to point out, there is a security implication here as well. Developers often code the cases they want to work first and, if there is enough time, fill in the error-handling code later, if at all.

When you are worried about security issues, however, reversing the order of those operations makes a lot of sense. If, for example, your application requires a cryptographic certificate to operate, one of the first issues a security programmer should think about is how that certificate can be revoked and replaced. Selecting certificate vendors from that perspective may be a very different proposition from the usual criteria (which is almost always cost). Building agile infrastructure from the start, in which the replacement of a crypto cert is straightforward, easy to do, and of minimal consequence to the end user, points the way toward a process for minimizing trust in any one vendor.

Developing an infrastructure that makes it easy to swap out certificates leads to the next interesting question: How will you know when to swap out that bad certificate? Perhaps the question can be turned around: How expensive is it to swap out a certificate—in money, effort, and customer displeasure? If it can be done cheaply, quickly, easily, and with no customer notice, perhaps it should be done frequently, just in case. If done properly, a frequent certificate change would help limit the scope of any damage, even if a problem is not noticed at first.

But there be dragons here! Some might read the previous paragraph and think that having certificates that expire weekly, for example, eliminates the need to monitor the infrastructure for problems, or the need to revoke a bad certificate. Far from it! All of those steps are necessary as well. Security is a belt-and-suspenders world.

An infrastructure that is well monitored for known threats is another part of the trust equation. If you are confident your infrastructure and personnel will make you aware of certain types of problems (or potential problems), then you can develop and practice procedures for handling those problems.

That covers the “known unknowns,” as former U.S. Secretary of Defense Donald Rumsfeld4 said, but what about the “unknown unknowns”? For several years Heartbleed was one of these. The fault in OpenSSL was present and exploitable for those who knew of it and knew how to do so. As of this writing, we do not know for certain if anybody did exploit it, but had someone done so, the nature of the flaw is such that an exploit would have left little or no trace, so it is very difficult to know for sure.

There are two major kinds of “unknown unknowns” to be aware of when providing a network service. The first are those unknowns you do not know about, but somebody else might know about and have disclosed or discussed publicly. Let’s call them “discoverable unknowns.” You do not know about them now, but you can learn about them, either from experience or from the experiences of others.

Discoverable unknowns are discoverable if and only if you make the effort to discover them. The pragmatic way to do this is to create an “intelligence service” of your own. The Internet is full of security resources if you care to use them. It is also full of misdirection, exaggeration, and egotism about security issues. The trick is learning which resources are gold and which are fool’s gold. That comes with practice and, sadly, often at the cost of mistakes both big and small.

A prudent, proactive organization has staff and budget devoted to acquiring and cultivating security resources. These include someone to evaluate likely websites, as well as read them regularly; subscriptions to information services; membership in security organizations; travel to conferences; and general cultivation of good contacts. It also includes doing favors for other organizations in similar situations and, if possible, becoming a good citizen and participant in the open-source world. If you help your friends, they will often help you when you need it.

The second type of unknowns can be called “unexpected unknowns.” You do not know what they are, you do not even know for sure that they exist, and you are not on the lookout for them specifically. But you can be on the lookout for them in general, by watching the behavior of your network. If you have a way of learning the baseline behavior of your network, system, or application, you can compare that baseline to what the system is doing now. This could include monitoring servers for unexpected processes, unexpected checksums of key software, files being created in unusual places, unexpected load changes, unexpected network or disk activity, failed attempts to execute privileged programs, or successful attempts that are out of the ordinary. For a network, you might look for unusual protocols, unexpected source or destination IP addresses, or unusually high- or low-traffic profiles. The better you can characterize what your system is supposed to be doing, the more easily you can detect when it is doing something else.

Detecting an anomaly is one thing, but following up on what you have detected is at least as important. In the early days of the Internet, Clifford Stoll,6 then a graduate student at Lawrence Berkeley Laboratories in California, noticed a 75-cent accounting error on some computer systems he was managing. Many would have ignored it, but it bothered him enough to track it down. That investigation led, step by step, to the discovery of an attacker named Markus Hess, who was arrested, tried, and convicted of espionage and selling information to the Soviet KGB.

Unexpected unknowns might be found, if they can be found at all, by reactive means. Anomalies must be noticed, tracked down, and explained. Logs must be read and understood. But defenses against known attacks can also prevent surprises from unknown ones. Minimizing the “attack surface” of a network also minimizes the opportunities an attacker has for compromise. Compartmentalization of networks and close characterization of regular traffic patterns can help detect something out of the ordinary.

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What Can You Do?

How can issues of trust be managed in a commercial, academic, or industrial computing environment?

The single most important thing a practitioner can do is to give up the idea that this task will ever be completed. There is no device to buy, no software to install, and no protocol to implement that will be a universal answer for all of your trust and security requirements. There will never come a time when you will be done with it and can move on to something else.

Security is a process. It is a martial art you can learn to apply by study, thought, and constant practice. If you do not drill and practice regularly, you will get rusty at it, and it will not serve you when you need it. Even if you do become expert at it, an attacker may sometimes overpower you. The better you get at the process, however, the smaller the number of opponents that can do you harm, the less damage they can do, and the quicker you can recover.

Here are some basic areas where you can apply your efforts.

Know whom you trust and what you trust them to do. Though it is an overused term, “Web of Trust” is descriptive of what you are building. Like any sophisticated construction, you should have a plan, a diagram, or some other form of enumeration of which trust mechanisms are needed to support your enterprise. The following entities might be on such a plan: datacenter provider (power, A/C, LAN); telecommunications link vendors; hardware vendors; paid software vendors; open source software providers; cryptographic certificate suppliers; time-source suppliers; systems administrators; database administrators; applications administrators; applications programmers; applications designers; security engineers.

Of course, mileage may vary, and there may be many more entities as well. Whatever is on the list you generate, perform the following exercise for each entry:

  • Determine whom this entity trusts to do the job and who trusts this entity.
  • Estimate the consequences if this entity were to fail to do the job properly.
  • Estimate the consequences if this entity were a bad actor trying to compromise the enterprise in some way (extract information without authorization, deny service, provide bad information to your customers or yourself, and so on).
  • Rate each consequence for severity.

Know what you would do if any of those entities lost your trust. Now that you have a collection of possible ways that your enterprise can be affected, sorted by severity, you can figure out what you would do for each item. This can be as simple or complicated as you are comfortable with, but remember that you are creating a key part of your operations handbook, so if your plans cannot be turned into actions when these circumstances occur, they will not be worth much.

Developing an infrastructure that makes it easy to swap out certificates leads to the next interesting question: How will you know when to swap out that bad certificate?

Here are some examples of the kinds of consequences and actions that might be needed:

  • A key open-source package is discovered to have a serious bug and must be: replaced with a newer, bug-fixed version; replaced with a different package with the same API; replaced with a different package with a different API; or mitigated until a fix can be developed. Your plan should be a good guide to handling any of those situations.
  • A key systems administrator has been providing network access to a potentially unfriendly third party. You must: determine the extent of information lost (or was your information modified?); determine if any systems were compromised with backdoor access; determine which other systems under the sys admin might be affected; figure out the best way of handling the personnel issues (firing, transfer, legal action).
  • A key data center is rendered unusable by a disaster or attack. You must: shift to a standby reserve location; or improvise a backup datacenter.

Practice, practice, practice. Having a plan is all very nice, but if it is in a dusty file cabinet, or worse yet, on a storage volume in a machine that is made unavailable by the very circumstances you are planning for, then it does not help anybody. Even if the plan is readily available, carrying it out for the first time during a crisis is a good way to ensure it will not work.

The best way to make sure that your plan is actionable is to practice. That means every plan needs to have a method of simulation of cause and evaluation of result. Sometimes that can be as easy as turning off a redundant server and verifying that service continues. Others are more complex to simulate. Even a tabletop exercise, in which people just talk about what is needed, is better than never practicing your contingency plan.

Practice can also take the form of regular operations. For example, Heartbleed required many service providers to revoke and reissue certificates. If that is a critical recovery operation for your enterprise, then find a way to work that procedure into your regular course of business, perhaps by revoking and reissuing a certificate once a month.

Other operations can also benefit from practice, such as restoring a file from backups; rebuilding an important server; transferring operations to a backup datacenter; or verifying the availability of backup power and your ability to switch over to it.

Set mousetraps. The most important step in defending against attackers (or Murphy’s Law) is acquiring the knowledge that you have a problem. If you understand your trust relationships—who is trusted with what and who is not trusted—then watching for violations of those relationships will be very instructive. Every violation will probably fall into one of these categories:

  • An undocumented but legitimate trust relationship. This might be sys admins doing their assigned work, for example, but that work was improperly overlooked when building the trust map.
  • A potentially reasonable but unconsidered potential trust relationship that must be evaluated and either added to the trust map or explicitly prohibited—for example, a sys admin doing unassigned but necessary work to keep a system operational.
  • An unreasonable or illegitimate use.

The only way to know which case it is will be to investigate each one and modify your trust map accordingly. As with all things of this nature, mousetraps must be periodically tested to see if they still work.

Vet your key people. Trusting a systems administrator often takes the form of management saying to sys admins, “Here are the keys to everything,” followed by more-or-less blind trust that those keys would not be abused. Or to quote science fiction author Robert Heinlein: “It’s amazing how much mature wisdom resembles being too tired.” That sort of blind trust is asking for trouble.

On the other hand, tracking sys admins closely and forcing them to ask permission for every privileged operation they wish to perform can hobble an organization. Chances are good that both the sys admins and the granters of permission will grow tired of this and the organization will move back toward blind trust.

Having a plan is all very nice, but if it is in a dusty file cabinet or on a storage volume in a machine made unavailable by the very circumstances you are planning for, then it does not help anybody.

A good way to navigate between these two rocky shoals is to hire good people and treat them well. Almost as important is communicating with them to reinforce the security and trust goals of your organization. If they know what must and must not be done and, at least in general principle, why those constraints are good, then the chances are greater they will act appropriately in a crunch.

Log what they do. Have somebody else review those logs regularly. Good people can make mistakes and sometimes even go astray. A regular non-privileged (in the security sense) employee should still have a reasonable expectation of workplace privacy, but a systems administrator should know he or she is being watched when performing sensitive tasks or accessing sensitive resources. In addition, encourage sys admins to perform extremely sensitive tasks with at least one other person of equal or higher clearance present. That way, someone else can attest the action taken was necessary and reasonable.

Wherever possible, log what the sys admins do with their privileges and have a third party review those logs regularly for anomalies. The third party should be distant enough from the systems administrators or other employees given trusted access so that no personal or professional relationships will obscure the interpretation of the logs.

Investigate what you suspect and act on what you find. Let your trusted people know in advance that is what you will do. Let them know their positions of responsibility make them the first suspects on the list if trust is violated.

Minimize your windows of vulnerability. Once you know ways in which you can be vulnerable, develop plans to minimize and mitigate those vulnerabilities. If you can close the hole, then close it. If you cannot close it, then limit what can be done through the hole. If you cannot limit what can be done, then limit who can do it and when it can be exploited. If you cannot limit anything, then at least measure whether an exploit is taking place. You may not have a perfect solution, but the more limits you put on a potential problem, the less likely it is that it will become a real problem.

Layer your security. When it comes to trust, you should not depend on any one entity for security. This is known as “defense in depth.” If you can have multiple layers of encryption, for example, each implemented differently (one depending on OpenSSL, for example, and the other using a different package), then a single vulnerability will not leave you completely exposed.

This is a good reason to look at every component of your enterprise and ask: What if these components were to be compromised?

Practice being agile. If a component were compromised, how would you replace it, and with what? How long would it take to switch over? Theories do not count here. You need to be prepared to switch packages or vendors or hardware in order to be adequately safe. How long will it take your purchasing department to cut paperwork for a new license, for example? How long to get that purchase order signed off? How long for the vendor to deliver?

This is not work you can do once and think you are ready. You need to revisit all components regularly and perform this kind of analysis for each of them as circumstances change.

Look at your network as an attacker would. Know the “as-built” configuration of your network, not just the “as-specified.” Remember the as-built configuration can change every day. This means you have to have people to measure the network, and tools to examine it. What network services does each component provide? Are those services needed? Are they available only to the places they are needed? Are all of the components fully patched? Are they instrumented to detect and report attack attempts? Does someone read those logs? What is the longest period of time between when an attack happens and when somebody notices it? Are there any events (such as holidays) when the length of time an attack goes unnoticed might increase?

The Internet abounds with free or inexpensive software for security analysis. These are tools often used by attackers and defenders. There is something to be learned by looking at your network through the same tools your attackers might use.

Track security issues and confirm they get fixed. If you find a problem, how is it tracked? Who is responsible for getting it into the tracking system, getting it to someone who can fix it, and getting it fixed? How do you measure the problem is present? Do you measure again after the fix is applied to ensure it worked?

Develop your own security intelligence resources. Does your organization have personnel who track the technology used for potential security issues? How often do they check? Are they listened to when they report a problem?

Any equipment, software, vendors, or people you depend on should be researched on a regular basis. Quality security-focused websites exist, but they are often surrounded and outnumbered by those with products to sell or misinformation to distribute. Having staff gain the expertise to distinguish the good from the bad is extremely valuable.

Plan for big-ticket problems. If you run a networked enterprise, whether you provide a public, private, or internal suite of services, you will find that trusted services will fail you, sooner or later. Repeatedly. How you respond to those failures of trust will become a big part of your company’s reputation. If you select your vendors, partners, and components wisely, seriously plan for responses to trouble situations, and act on your plans when the time comes, then you will fare much better in the long run than those whose crisis planning is filed under “Luck.”

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The problem of trust is not new. If anything, the only new part is the mistaken impression that things can be trusted, because so many new things seem to be trustworthy. It is a sometimes-comforting illusion, but an illusion nonetheless. To build anything of value, you will have to place your trust in some people, products, and services. Placing that trust wisely is a skill that is best learned over time. Mistakes will abound along the way. Planning for your mistakes and the mistakes of others is essential to trusting.

It is generally better, faster, and safer to take something that meets good standards of trustworthiness and add value to it—by auditing it, layering on top of it, or adding to the open source—than it is to roll your own. Be prepared to keep a wary eye on the components you select, the system you include them in, and the people who build and maintain that system. Always plan for trouble, because trouble will surely come your way.

You must have some trust if you want to get anything done, but you cannot allow yourself to be complacent. Thomas Jefferson said, “Eternal vigilance is the price of liberty.” It is the price of security as well.

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Thanks to Jim Maurer and George Neville-Neil of the ACM Queue Editorial Board for encouraging and supporting this article. An extended version of this article is available at

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