Kerckhoffs' principle

As explained in Real-World Cryptography

Kerckhoffs' principle states that a cryptographic system should remain secure even when its algorithm is public, with secrecy relying on the key.

Imagine an enemy learning exactly how two people encrypt their messages. The system can still be secure if the secret key remains unknown. Kerckhoffs' principle says security should depend on the key, not on hiding the algorithm. section 1.3

Apply the principle by separating what may be public from what must remain secret:

• Publish and scrutinize cryptographic algorithms rather than relying on enemies not discovering them. section 1.3
• Protect the secret keys supplied to those algorithms. section 1.3
• Treat AES as an example of a widely studied algorithm used for encryption, including web browsing. section 1.3

Known algorithm, unknown key

Alice and Bob can let their enemies know their encryption algorithm. The messages remain protected because the enemies do not know the secret key. section 1.3

Figure 1.4 The cryptographic algorithms you have learned so far. AES is an instantiation of a symmetric encryption algorithm, which is a cryptographic primitive that is part of the broader class of symmetric cryptographic algorithms.

Use the algorithm map to place AES within symmetric encryption and broader symmetric cryptography. section 1.3

How Real-World Cryptography covers it

How deep it goes

Defines the principle through an adversarial scenario and explains its reliance on secret keys.

Examples

Uses Alice and Bob, enemy discovery of algorithms, AES, and everyday web browsing as examples.

What it assumes

Assumes basic familiarity with encryption, algorithms, and secret keys.

What you can do after

Evaluate whether a cryptographic design depends on key secrecy rather than algorithm secrecy.

How it connects

Connects public algorithms with secret keys, AES, symmetric encryption, and cryptographic standards.

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Related concepts

• security through obscuritycontrasts with · Security through obscurity is a security approach that relies on concealing system designs, implementations, or configurations to impede attacks.

This explainer was generated by Manning's knowledge graph from the text of Real-World Cryptography. The section links point to the parts of the book it draws on.