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Kerckhoffs’ principle

Kerckhoffs’ principle

(also Kerckhoffs’ law, Shannon’s maxim)

Kerckhoffs’ principle definition

Kerckhoffs’ principle is a fundamental concept in cryptography. It states that the security of a cryptographic system shouldn’t rely on the secrecy of the algorithm. Instead, it should be based on the secrecy of the cryptographic key. A good cryptographic system should remain secure even if the algorithm used is known. It’s now essential for modern cryptography — it encourages open design and analysis of cryptographic algorithms.

It was created by the Dutch cryptographer Auguste Kerckhoffs. Later popularized by the American mathematician and cryptographer Claude Shannon.

See also: cryptographic protocol, cryptographic key

Benefits of Kerckhoffs’ principle:

  • Security through transparency. Making the algorithm public allows experts tcheckte its strength. This process helps identify and address potential vulnerabilities and weaknesses in the algorithm.
  • Independence from obscurity. Relying on the secrecy of an algorithm for security is flawed because algorithms may become compromised. It can happen accidentally or through reverse engineering. In contrast, strong cryptographic keys provide the primary line of defense against attacks.
  • Interoperability: Published algorithms promote interoperability among different systems and applications. It allows different parties to communicate securely using the same standardized cryptographic algorithms.
  • Algorithm Agility: Following Kerckhoffs’ principle encourages adaptability. A cryptographic algorithm gets replaced with a more secure one if it becomes compromised or outdated.

Uses of Kerckhoffs’ principle

  • Cryptography. Kerckhoffs’ principle forms the basis for the design of modern cryptographic systems. These systems assume that an attacker has complete knowledge of the cryptographic algorithm. That way, the system’s security relies on the secrecy of the keys.
  • Information Security. In broader terms, the principle means that “security through obscurity” is insufficient. Instead, systems should be designed to be secure even when attackers know everything about how they work.
  • Software Design. The source code of security-critical software (like encryption algorithms) is open to the public. This method allows extensive peer review to identify and fix vulnerabilities. An example is the OpenSSL project, which provides robust and widely-used encryption functionalities.
  • Secure Communications. In communication protocols, the protocol design is open and standardized. Their security relies solely on using secret keys during the encryption and decryption processes. Not on the obscurity of the protocol design.
  • Secure Hardware Design. In designing hardware like Smart Cards and Hardware Security Modules (HSMs), Kerckhoffs’ principle is applied. The design and functionality of these devices are often publicly available, but the keys used within them are kept secret to maintain their security.

Further reading

Ultimate digital security