Editing Key exchange (section)

{{Short description|Cryptographic method}}
{{For|the film|Key Exchange}}
{{Redirect|Kex|other uses|KEX (disambiguation)|and|KEXS (disambiguation)}}
{{More citations needed|date=November 2014}}

'''Key exchange''' (also '''key establishment''') is a method in [[cryptography]] by which [[cryptographic keys]] are exchanged between two parties, allowing use of a cryptographic [[algorithm]].
[[File:Public key shared secret.svg|thumb|250px|right| In the [[Diffie–Hellman key exchange]] scheme, each party generates a public/private key pair and distributes the public key. After obtaining an authentic copy of each other's public keys, Alice and Bob can compute a shared secret offline. The shared secret can be used, for instance, as the key for a [[Symmetric-key algorithm|symmetric cipher]].]]

If the sender and receiver wish to exchange encrypted messages, each must be equipped to encrypt messages to be sent and decrypt messages received. The nature of the equipping they require depends on the [[encryption]] technique they might use. If they use a [[code (cryptography)|code]], both will require a copy of the same [[codebook]]. If they use a [[cipher]], they will need appropriate keys. If the cipher is a [[symmetric key|symmetric key cipher]], both will need a copy of the same key. If it is an [[public key|asymmetric key cipher]] with the public/private key property, both will need the other's public key.