Security through obscurity

In security engineering, security through obscurity (or security by obscurity) is the reliance on the secrecy of the design or implementation as the main method of providing security for a system or component of a system. A system or component relying on obscurity may have theoretical or actual security vulnerabilities, but its owners or designers believe that if the flaws are not known, that will be sufficient to prevent a successful attack. Security experts have rejected this view as far back as 1851, and advise that obscurity should never be the only security mechanism.

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, whose source code is publicly available to anyone, and is generally regarded as a military-grade cryptosystem.

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