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Security Fundamentals & Crypto · Foundational

Diffie-Hellman (DH)

Key agreement protocol that lets two parties derive a shared secret over an insecure channel.

Definition

Diffie-Hellman (1976) relies on the difficulty of the discrete logarithm problem. Each party combines its private value with the other's public value to compute the same secret without sending it. Unauthenticated DH is vulnerable to on-path attacks, so it is combined with signatures or certificates.

Example

IPsec IKE uses DH groups such as group 14 (2048-bit MODP) or group 19 (256-bit ECP) to derive keys.

Exam tip

DH provides key exchange, not encryption or signatures; DH groups in IKE define its strength.

Don't confuse it with

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