Editing Cryptographic protocol (section)

{{short description|Aspect of cryptography}}
A '''cryptographic protocol''' is an abstract or concrete [[Communications protocol|protocol]] that performs a [[information security|security]]-related function and applies [[cryptographic]] methods, often as sequences of [[cryptographic primitive]]s. A protocol describes how the algorithms should be used and includes details about data structures and representations, at which point it can be used to implement multiple, interoperable versions of a program.<ref>{{cite web |url= http://www.ccs-labs.org/~dressler/teaching/netzsicherheit-ws0304/07_CryptoProtocols_2on1.pdf |title= Cryptographic Protocol Overview |date= 2015-10-23 |access-date= 2015-10-23 |archive-url= https://web.archive.org/web/20170829004310/http://www.ccs-labs.org/~dressler/teaching/netzsicherheit-ws0304/07_CryptoProtocols_2on1.pdf |archive-date= 2017-08-29 |url-status= dead }}</ref>

Cryptographic protocols are widely used for secure application-level data transport. A cryptographic protocol usually incorporates at least some of these aspects:

* [[Key agreement]] or establishment
* Entity [[authentication]]
* Symmetric [[encryption]] and message authentication [[key (cryptography)| ]] material construction
* Secured application-level data transport
* [[Non-repudiation]] methods
* [[Secret sharing]] methods
* [[Secure multi-party computation]]

For example, [[Transport Layer Security]] (TLS) is a cryptographic protocol that is used to secure web ([[HTTPS]]) connections.<ref>{{Cite journal |last1=Chen |first1=Shan |last2=Jero |first2=Samuel |last3=Jagielski |first3=Matthew |last4=Boldyreva |first4=Alexandra |last5=Nita-Rotaru |first5=Cristina |date=2021-07-01 |title=Secure Communication Channel Establishment: TLS 1.3 (over TCP Fast Open) versus QUIC |journal=Journal of Cryptology |language=en |volume=34 |issue=3 |pages=26 |doi=10.1007/s00145-021-09389-w |s2cid=235174220 |issn=0933-2790|doi-access=free }}</ref> It has an entity authentication mechanism, based on the [[X.509]] system; a key setup phase, where a [[symmetric encryption]] key is formed by employing public-key cryptography; and an application-level data transport function. These three aspects have important interconnections. Standard TLS does not have non-repudiation support.

There are other types of cryptographic protocols as well, and even the term itself has various readings; Cryptographic ''application'' protocols often use one or more underlying [[key agreement|key agreement method]]s, which are also sometimes themselves referred to as "cryptographic protocols". For instance, TLS employs what is known as the [[Diffie–Hellman key exchange]], which although it is only a part of TLS ''per se'', Diffie–Hellman may be seen as a complete cryptographic protocol in itself for other applications.