Diffie–Hellman key exchange

Diffie–Hellman key exchange is a protocol that lets two parties derive a shared secret over a public channel without transmitting the secret itself.

Discrete logarithm problem: The problem of recovering an exponent from a base and its power in a finite group. Its computational difficulty underlies the classic protocol’s security.
Transport Layer Security: A protocol that protects communications between applications over a network. TLS uses authenticated key exchanges to establish session keys.
Whitfield Diffie: An American cryptographer who helped introduce public-key cryptography and key agreement. He co-developed the key-exchange idea with Martin Hellman.
RSA: A public-key cryptosystem whose security is associated with factoring large composite integers. RSA can transport keys through encryption, whereas Diffie–Hellman derives a shared secret through agreement.
Cyclic group: A group generated by repeated powers of one element. Diffie–Hellman computes powers of a generator in a chosen group.
Ephemeral Diffie–Hellman: A Diffie–Hellman exchange using fresh, temporary key pairs for each session. Temporary secrets enable forward secrecy when long-term keys are later exposed.
Martin Hellman: An American cryptographer known for foundational work on public-key cryptography. He co-developed the protocol and published it with Diffie.
Merkle’s Puzzles: A key-establishment method in which a party solves one of many computational puzzles to create a shared key. It is an earlier, less efficient public-key approach to establishing shared secrets.
Modular exponentiation: Exponentiation whose result is reduced modulo an integer. The parties exchange modular powers and independently compute the same shared value.
Elliptic-curve Diffie–Hellman: A Diffie–Hellman key agreement using scalar multiplication on an elliptic-curve group. It provides the same key-agreement idea with different groups and compact keys.

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