I find that legacy code poses a unique challenge for organizations rolling out a new security process.  Often, the resources dedicated to maintaining older code are a small fraction of those devoted to new features or products.  Furthermore, the original developers for such features have often moved on, leaving no subject matter experts to drive reviews.  The astute reader will ask “How do I apply the principles of the Microsoft SDL to legacy code when I have no development resources and nobody knows how it works?”

The answer is “Start small, and build expertise over time.”

A Rising Tide Lifts All Boats

The best thing a security engineering team can do to improve security in the short term is to drive code quality, and the first step in this process is to define and enforce a secure coding standard.  This helps on two fronts: 

1.       It will improve code quality and reduce implementation flaws across the entire code base.  Unlike other security processes, driving a secure coding standard is relatively easy to accomplish across an entire code base, regardless of the code’s age, by a focused security team.  That is not to say that it is easy without qualification – a large batch of spaghetti code will require a lot of work to untangle!  Such an effort can only be called “easy” when compared to, say, comprehensive identification and remediation of design flaws across legacy features.  Even so, improving code quality through the use of secure coding standards offers a unique combination of high impact, applicability to features, and ability to be carried out by a core team that makes it a sensible first step.

2.       The security team might notice that some sections of code have more standards violations or outright flaws than others.  This is an instance of vulnerability clustering, a concept that has been used to predict vulnerability rates and improve quality in the functional realm.  The evidence is anecdotal, but it stands to reason that portions of code that consistently violate secure coding standards are good places to start looking for other classes of security flaw.  These are security hotspots, and should be high on the prioritized list for further review.

Security testing may also be applied to legacy code, but initial activities should be considered on a case-by-case basis based on the expected return on investment.  Such testing ranges from using inexpensive off-the-shelf tools to exercise common interfaces to rather expensive custom testing and formal analysis.  It is worthwhile to begin with off-the-shelf tools, such as those that target file parsers or web applications, and tools created as part of your greater secure development efforts.  These can help identify easily-found flaws and suggest improvements to the coding standards.  Comprehensive security testing, on the other hand, is best tackled after the Legacy Security Push.

The Legacy Security Push

Coding standards and basic testing provide bang for the buck, but formal security processes seek to provide security assurance.  The challenge for legacy code is that it needs to play catch-up.  Security processes that occur early in the development cycle, such as requirements analysis, design review, and threat modeling, are particularly difficult to achieve years after the fact.  The main goal of the Legacy Security Push is to create the deliverables from these efforts, the most important of which are security requirements and a full risk analysis.

It may sound trivial, but security requirements are essential.  Not only do they define proper operation for the system in question, they also define assumptions that are suitable for relying systems.   It is very common to find security flaws in legacy systems that arise from well-intentioned but incorrect assumptions such as “I assume that the Foo authenticates server Bar when initiating a bank transfer.”  It stands to reason that Foo would do so for such an important activity, but this assumption must be validated.  It is very common for older features to have been deployed in and written for different environments where the security assumptions that are "obvious" today just didn't apply at the time.

When reviewing legacy systems, the first step is to identify such requirements.  If the original architects, developers or managers are available, they can provide valuable insight at this stage.  More often than not this is not the case, and analysis must instead rely on what documentation is present and interaction between the software and its consumers.  The goal is the same as in requirements analysis during project inception, except that in this case one must turn the process on its head and reverse engineer requirements from system behavior.  At the conclusion of this effort, requirements can be theorized – “Foo must authenticate its server Bar before initiating a bank transfer.” 

Risk analysis can be performed once a plausible set of requirements have been identified.  Threat modeling is a more structured means of performing such an analysis, with the eventual goal of identifying means by which requirements can be violated by an attacker. 

As with requirements analysis, original developers would be a valuable resource to consult.  With or without such help, the first step is to identify how the software works.  In many cases, help is not available and performing this task requires a great deal of effort.  For features of moderate size, this author has spent upwards of a month reading code, using process profiling tools, and walking through the software with a debugger to identify program flow and security-sensitive functionality.

Once completed, actual system behavior should be documented and compared against the requirements theorized.   It might be that the requirements should be re-evaluated (New requirement:  Do not assume that Foo requires server authentication) or the system may need to be changed (New bug:   Foo does not verify the CN for Bar).  At the end, this information should be sufficient to support a comprehensive threat modeling exercise where security requirements, risks, and their mitigations can be documented.

Next Steps

Bringing a legacy feature up to par with its newer kin requires a relatively small number of items:  improved code quality, clear security requirements, and a thorough threat model.  As we have seen, performing even these tasks is quite the effort!  I am sure that it is little comfort to be reminded that accomplishing these tasks has simply laid the foundation, and that the true benefit is that the newly-reviewed legacy feature is able to participate fully in the security processes that remain: reviewing cross-component security requirements and assumptions, comprehensive testing, and incident planning, to name a few.

Unfortunately, there is no silver bullet in security assurance.  The soundness of the design and implementation of legacy software is just as important as in newer software, which is why any complete secure software development process will look backwards as well as forwards.  Feature by feature, from higher priority to lower, the overall security of the software improves as legacy code receives the full security treatment it deserves.

The scannable card serves as proof that a background check has been performed and it contains features aimed at preventing misuse. In addition to a photograph, the card contains a smart chip that carries a copy of the holder's fingerprint. Port and delivery workers, cargo handlers, and other employees who must venture into sensitive or secure areas will be required to submit to a fingerprint scan before entering those locations. The scanning machine will automatically perform a match analysis with the fingerprint embedded in the smart chip.

This is a great application for these cards.

Conventional wisdom holds that terrorism is inherently political, and that people become terrorists for political reasons. This is the "strategic" model of terrorism, and it's basically an economic model. It posits that people resort to terrorism when they believe -- rightly or wrongly -- that terrorism is worth it; that is, when they believe the political gains of terrorism minus the political costs are greater than if they engaged in some other, more peaceful form of protest. It's assumed, for example, that people join Hamas to achieve a Palestinian state; that people join the PKK to attain a Kurdish national homeland; and that people join al-Qaida to, among other things, get the United States out of the Persian Gulf.

If you believe this model, the way to fight terrorism is to change that equation, and that's what most experts advocate. Governments tend to minimize the political gains of terrorism through a no-concessions policy; the international community tends to recommend reducing the political grievances of terrorists via appeasement, in hopes of getting them to renounce violence. Both advocate policies to provide effective nonviolent alternatives, like free elections.

Historically, none of these solutions has worked with any regularity. Max Abrahms, a predoctoral fellow at Stanford University's Center for International Security and Cooperation, has studied dozens of terrorist groups from all over the world. He argues that the model is wrong. In a paper published this year in International Security that -- sadly -- doesn't have the title "Seven Habits of Highly Ineffective Terrorists," he discusses, well, seven habits of highly ineffective terrorists. These seven tendencies are seen in terrorist organizations all over the world, and they directly contradict the theory that terrorists are political maximizers:

Terrorists, he writes, (1) attack civilians, a policy that has a lousy track record of convincing those civilians to give the terrorists what they want; (2) treat terrorism as a first resort, not a last resort, failing to embrace nonviolent alternatives like elections; (3) don't compromise with their target country, even when those compromises are in their best interest politically; (4) have protean political platforms, which regularly, and sometimes radically, change; (5) often engage in anonymous attacks, which precludes the target countries making political concessions to them; (6) regularly attack other terrorist groups with the same political platform; and (7) resist disbanding, even when they consistently fail to achieve their political objectives or when their stated political objectives have been achieved.

Abrahms has an alternative model to explain all this: People turn to terrorism for social solidarity. He theorizes that people join terrorist organizations worldwide in order to be part of a community, much like the reason inner-city youths join gangs in the United States.

The evidence supports this. Individual terrorists often have no prior involvement with a group's political agenda, and often join multiple terrorist groups with incompatible platforms. Individuals who join terrorist groups are frequently not oppressed in any way, and often can't describe the political goals of their organizations. People who join terrorist groups most often have friends or relatives who are members of the group, and the great majority of terrorist are socially isolated: unmarried young men or widowed women who weren't working prior to joining. These things are true for members of terrorist groups as diverse as the IRA and al-Qaida.

For example, several of the 9/11 hijackers planned to fight in Chechnya, but they didn't have the right paperwork so they attacked America instead. The mujahedeen had no idea whom they would attack after the Soviets withdrew from Afghanistan, so they sat around until they came up with a new enemy: America. Pakistani terrorists regularly defect to another terrorist group with a totally different political platform. Many new al-Qaida members say, unconvincingly, that they decided to become a jihadist after reading an extreme, anti-American blog, or after converting to Islam, sometimes just a few weeks before. These people know little about politics or Islam, and they frankly don't even seem to care much about learning more. The blogs they turn to don't have a lot of substance in these areas, even though more informative blogs do exist.

All of this explains the seven habits. It's not that they're ineffective; it's that they have a different goal. They might not be effective politically, but they are effective socially: They all help preserve the group's existence and cohesion.

This kind of analysis isn't just theoretical; it has practical implications for counterterrorism. Not only can we now better understand who is likely to become a terrorist, we can engage in strategies specifically designed to weaken the social bonds within terrorist organizations. Driving a wedge between group members -- commuting prison sentences in exchange for actionable intelligence, planting more double agents within terrorist groups -- will go a long way to weakening the social bonds within those groups.

We also need to pay more attention to the socially marginalized than to the politically downtrodden, like unassimilated communities in Western countries. We need to support vibrant, benign communities and organizations as alternative ways for potential terrorists to get the social cohesion they need. And finally, we need to minimize collateral damage in our counterterrorism operations, as well as clamping down on bigotry and hate crimes, which just creates more dislocation and social isolation, and the inevitable calls for revenge.

This essay previously appeared on Wired.com.

Conventional wisdom holds that terrorism is inherently political, and that people become terrorists for political reasons. This is the "strategic" model of terrorism, and it's basically an economic model. It posits that people resort to terrorism when they believe -- rightly or wrongly -- that terrorism is worth it; that is, when they believe the political gains of terrorism minus the political costs are greater than if they engaged in some other, more peaceful form of protest. It's assumed, for example, that people join Hamas to achieve a Palestinian state; that people join the PKK to attain a Kurdish national homeland; and that people join al-Qaida to, among other things, get the United States out of the Persian Gulf.

If you believe this model, the way to fight terrorism is to change that equation, and that's what most experts advocate. Governments tend to minimize the political gains of terrorism through a no-concessions policy; the international community tends to recommend reducing the political grievances of terrorists via appeasement, in hopes of getting them to renounce violence. Both advocate policies to provide effective nonviolent alternatives, like free elections.

Historically, none of these solutions has worked with any regularity. Max Abrahms, a predoctoral fellow at Stanford University's Center for International Security and Cooperation, has studied dozens of terrorist groups from all over the world. He argues that the model is wrong. In a paper (.pdf) published this year in International Security that -- sadly -- doesn't have the title "Seven Habits of Highly Ineffective Terrorists," he discusses, well, seven habits of highly ineffective terrorists. These seven tendencies are seen in terrorist organizations all over the world, and they directly contradict the theory that terrorists are political maximizers:

Terrorists, he writes, (1) attack civilians, a policy that has a lousy track record of convincing those civilians to give the terrorists what they want; (2) treat terrorism as a first resort, not a last resort, failing to embrace nonviolent alternatives like elections; (3) don't compromise with their target country, even when those compromises are in their best interest politically; (4) have protean political platforms, which regularly, and sometimes radically, change; (5) often engage in anonymous attacks, which precludes the target countries making political concessions to them; (6) regularly attack other terrorist groups with the same political platform; and (7) resist disbanding, even when they consistently fail to achieve their political objectives or when their stated political objectives have been achieved.

Abrahms has an alternative model to explain all this: People turn to terrorism for social solidarity. He theorizes that people join terrorist organizations worldwide in order to be part of a community, much like the reason inner-city youths join gangs in the United States.

The evidence supports this. Individual terrorists often have no prior involvement with a group's political agenda, and often join multiple terrorist groups with incompatible platforms. Individuals who join terrorist groups are frequently not oppressed in any way, and often can't describe the political goals of their organizations. People who join terrorist groups most often have friends or relatives who are members of the group, and the great majority of terrorist are socially isolated: unmarried young men or widowed women who weren't working prior to joining. These things are true for members of terrorist groups as diverse as the IRA and al-Qaida.

For example, several of the 9/11 hijackers planned to fight in Chechnya, but they didn't have the right paperwork so they attacked America instead. The mujahedeen had no idea whom they would attack after the Soviets withdrew from Afghanistan, so they sat around until they came up with a new enemy: America. Pakistani terrorists regularly defect to another terrorist group with a totally different political platform. Many new al-Qaida members say, unconvincingly, that they decided to become a jihadist after reading an extreme, anti-American blog, or after converting to Islam, sometimes just a few weeks before. These people know little about politics or Islam, and they frankly don't even seem to care much about learning more. The blogs they turn to don't have a lot of substance in these areas, even though more informative blogs do exist.

All of this explains the seven habits. It's not that they're ineffective; it's that they have a different goal. They might not be effective politically, but they are effective socially: They all help preserve the group's existence and cohesion.

This kind of analysis isn't just theoretical; it has practical implications for counterterrorism. Not only can we now better understand who is likely to become a terrorist, we can engage in strategies specifically designed to weaken the social bonds within terrorist organizations. Driving a wedge between group members -- commuting prison sentences in exchange for actionable intelligence, planting more double agents within terrorist groups -- will go a long way to weakening the social bonds within those groups.

We also need to pay more attention to the socially marginalized than to the politically downtrodden, like unassimilated communities in Western countries. We need to support vibrant, benign communities and organizations as alternative ways for potential terrorists to get the social cohesion they need. And finally, we need to minimize collateral damage in our counterterrorism operations, as well as clamping down on bigotry and hate crimes, which just creates more dislocation and social isolation, and the inevitable calls for revenge.

---

Bruce Schneier is Chief Security Technology Officer of BT, and author of Beyond Fear: Thinking Sensibly About Security in an Uncertain World.

One of the main problems in counterterrorism today is that there are so many people and vehicles, and so much data and material, moving through globalization's myriad networks that it seems virtually impossible to track it all effectively. Nowhere has this problem been more acute than on the high seas.

In 2006, Adm. Harry Ulrich, then U.S. commander of NATO Naval Forces Europe, decided to do something about it. Despite having virtually no resources, his dream was to transpose the global air-traffic control system onto sea traffic.

Worldwide, aircraft are transparent, because they're all required to carry an identification beacon that allows them to be tracked leaving and entering airports, and monitored between airports, by a global network of sensors. Act suspiciously and somebody's fighter aircraft will soon be on your tail.

No such pervasive system currently exists globally for maritime traffic. While bigger ships carry an ID beacon similar to aircraft, without a shared monitoring network, that's like tracking only selected commercial jets and giving everyone else a pass.
So Ulrich, upon taking command, asked a simple question: "If we can do that in the air, why can't we do it on the sea?" He made a point of pioneering his sea-traffic-control effort first inside the Mediterranean, where NATO's southern naval forces have historically been concentrated, but his real target was waters off Africa -- the most ungoverned maritime space in the world.

Ulrich knew the U. S. Navy couldn't do it alone, much less bring Africa's meager coast-guard-like navies up to snuff so they could do it on their own. So he quickly created a network of assets -- both public and private -- to manage that space, modeling his monitoring system on international air-traffic control.

Ulrich began stitching together a network of shore-based sensors ringing the Mediterranean. His naval command then began initial monitoring by tapping into the International Maritime Organization's existing Automated Identification System, transforming NATO's ability to track ship traffic in the Med.

Almost overnight, NATO went from tracking dozens of ships on the Mediterranean to thousands, and instead of getting the data sometimes up to 72 hours late, now the contacts were being tracked in one to five minutes -- to an accuracy within 50 feet on the earth's surface.

When the classic big-firm systems integrators told Ulrich it would be too costly to pull it off, the admiral turned to the Volpe Center in Cambridge, Massachusetts, a U.S. Department of Transportation research center. Instead of hundreds of millions of dollars, Ulrich's initial network cost $900,000. The shore-based receivers are small, roughly the size of a radar dish you might find on a pleasure craft.

The strength of the system is a function of its reach: the more countries join, the larger the shared operational picture. By the time Ulrich retired at the end of 2007, he had enlisted 32 countries throughout the Mediterranean, the North Atlantic, along the west coast of Africa, around the Black Sea, and in the Pacific. Today, the network continues to spread around the planet.

With Ulrich's system in place, local police, coast guards, and border patrols catch most bad guys, obviating American military responses. As Harry told me for an article I wrote about his work in a fall 2007 issue of Esquire, "I don't do defense; I do security. When you talk defense, you talk containment and mutually assured destruction. When you talk security, you talk collaboration and networking. This is the future."

The admiral's legacy program, the Maritime Safety and Security Information System, earned the Volpe Center a prestigious "Innovations in American Government" award this month from Harvard University's Ash Institute for Democratic Governance and Innovation.