Security through obscurity

In security engineering, security through obscurity is the use of secrecy of the design or implementation to provide security. A system relying on security through obscurity may have theoretical or actual security vulnerabilities, but its owners or designers believe that if the flaws are not known, then attackers will be unlikely to find them. A system may use security through obscurity as a defense in depth measure; while all known security vulnerabilities would be mitigated through other measures, public disclosure of products and versions in use makes them early targets for newly discovered vulnerabilities in those products and versions. An attacker's first step is usually information gathering; this step may be delayed by security through obscurity. The technique stands in contrast with security by design and open security, although many real-world projects include elements of all strategies.

Security through obscurity is discouraged and not recommended by standards bodies. The National Institute of Standards and Technology (NIST) in the United States specifically recommends against this practice: "System security should not depend on the secrecy of the implementation or its components."

Background

An early opponent of security through obscurity was the locksmith Alfred Charles Hobbs, who in 1851 demonstrated to the public how state-of-the-art locks could be picked and who, in response to concerns that exposing security flaws in the design of locks could make them more vulnerable to criminals, said "Rogues are very keen in their profession, and know already much more than we can teach them."

There is scant formal literature on the issue of security through obscurity. Books on security engineering cite Kerckhoffs' doctrine from 1883, if they cite anything at all. For example, in a discussion about secrecy and openness in Nuclear Command and Control:

[T]he benefits of reducing the likelihood of an accidental war were considered to outweigh the possible benefits of secrecy. This is a modern reincarnation of Kerckhoffs' doctrine, first put forward in the nineteenth century, that the security of a system should depend on its key, not on its design remaining obscure.

In the field of legal academia, Peter Swire has written about the trade-off between the notion that "security through obscurity is an illusion" and the military notion that "loose lips sink ships" as well as how competition affects the incentives to disclose.

The principle of security through obscurity was more generally accepted in cryptographic work in the days when essentially all well-informed cryptographers were employed by national intelligence agencies, such as the National Security Agency. Now that cryptographers often work at universities, where researchers publish many or even all of their results, and publicly test others' designs, or in private industry, where results are more often controlled by patents and copyrights than by secrecy, the argument has lost some of its former popularity. An example is PGP released as source code, and generally regarded (when properly used) as a military-grade cryptosystem.

Security through minority

A variant of the basic approach is to rely on the properties (including whatever vulnerabilities might be present) of a product which is not widely adopted, thus lowering the prominence of those vulnerabilities (should they become known) against random or even automated attacks. This approach has a variety of names, "minority" being the most common. Others are "rarity", "unpopularity", "scarcity", and "lack of interest".

This variant is most commonly encountered in explanations of why the number of known vulnerability exploits for products with the largest market share tends to be higher than a linear relationship to market share would suggest, but is also a factor in product choice for some large organizations.

Security through minority may be helpful for organizations who will not be subject to targeted attacks, suggesting the use of a product in the long tail. However, finding a new vulnerability in a market leading product is likely harder than for obscure products, as the low hanging fruit vulnerabilities are more likely to have already turned up, which may suggest these products are better for organisations who expect to receive many targeted attacks. The issue is further confused by the fact that new vulnerabilities in minority products cause all known users of that (perhaps easily identified) product to become targets. With market leading products, the likelihood of being randomly targeted with a new vulnerability remains greater.

The whole issue is closely linked with, and in a sense depends upon, the widely used term security through diversity - the wide range of "long tail" minority products is clearly more diverse than a market leader in any product type, so a random attack will be less likely to succeed.

Security through obsolescence is, for example, using obsolete network protocols (e.g. IPX instead of TCP/IP) to make attacks from the Internet difficult. ATMs often use X.25 networks.

Historical notes

There are conflicting stories about the origin of this term. Fans of MIT's Incompatible Timesharing System (ITS) say it was coined in opposition to Multics users down the hall, for whom security was far more an issue than on ITS. Within the ITS culture the term referred, self-mockingly, to the poor coverage of the documentation and obscurity of many commands, and to the attitude that by the time a tourist figured out how to make trouble he'd generally got over the urge to make it, because he felt part of the community.

One instance of deliberate security through obscurity on ITS has been noted: the command to allow patching the running ITS system (altmode altmode control-R) echoed as ##^D. Typing Alt Alt Control-D set a flag that would prevent patching the system even if the user later got it right.

Open source software is deemed unsuitable for and thus discourages security through obscurity, because its source code is public knowledge.

See also

• Steganography
• Code morphing
• Kerckhoffs' principle
• Need to know
• Obfuscated code
• Presumed security
• Secure by design
• AACS encryption key controversy
• Code talker

External links

• Eric Raymond on Cisco's IOS source code 'release' v Open Source
• Computer Security Publications: Information Economics, Shifting Liability and the First Amendment by Ethan M. Preston and John Lofton
• "Security Through Obscurity" Ain't What They Think It Is at the Wayback Machine (archived February 2, 2007) by Jay Beale
• Secrecy, Security and Obscurity & The Non-Security of Secrecy by Bruce Schneier
• "Security through obsolescence", Robin Miller, linux.com, June 6, 2002