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'''Identity-based cryptography''' is a type of [[public-key cryptography]] in which a publicly known string representing an individual or organization is used as a [[public key]]. The public string could include an email address, ___domain name, or a physical IP address.
[[File:TexasDMV_Message_example.jpg|thumb|Depiction of message from txdmv for unable to verify identity]]
The first implementation of identity-based signatures and an email-address based [[public-key infrastructure]] ('''PKI''') was developed by [[Adi Shamir]] in 1984,<ref>
Shamir similarly proposed [[identity-based encryption]], which appeared particularly attractive since there was no need to acquire an identity's public key prior to encryption. However, he was unable to come up with a concrete solution, and identity-based encryption remained an open problem for many years. The first practical implementations were finally devised by Sakai in 2000,<ref>
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|series=Symposium on cryptography and information security}}
</ref> and Boneh and Franklin in 2001.<ref>
{{cite
| last1 = Dan | first1 = Boneh
| last2 = Matt | first2 = Franklin
| title = Identity-based encryption from the Weil pairing
|
| publisher = Springer
|
| year=2001
| volume = 2139/2001 | pages = 213–229
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}}</ref> These solutions were based on [[pairing|bilinear pairings]]. Also in 2001, a solution was developed independently by [[Clifford Cocks]].<ref>
{{cite book
|title = Cryptography and Coding
|
|
|year = 2001
▲ |pages = 360–363
▲ |url = . http://www.cesg.gov.uk/site/ast/idpkc/media/ciren.pdf
▲ |publisher = Springer
|url-status = dead
▲ |doi = 10.1007/3-540-45325-3_32
▲ |archiveurl = https://web.archive.org/web/20070206084247/http://www.cesg.gov.uk/site/ast/idpkc/media/ciren.pdf
|isbn = 978-3-540-43026-1▼
▲ |archivedate = 2007-02-06
}}</ref><ref>{{cite web|
▲|isbn = 978-3-540-43026-1
▲ |citeseerx = 10.1.1.116.5477
▲ }}</ref><ref>{{cite web|archiveurl=https://web.archive.org/web/20150627063023/http://www.bristol.ac.uk/pace/graduation/honorary-degrees/hondeg08/cocks.html|archivedate=2015-06-27|url=http://www.bristol.ac.uk/pace/graduation/honorary-degrees/hondeg08/cocks.html|publisher=University of Bristol|title=Dr Clifford Cocks CB, Honorary Doctor of Science}}</ref>
Closely related to various identity-based encryption schemes are identity based key agreement schemes. One of the first identity based key agreement algorithms was published in 1986, just two years after Shamir's identity based signature. The author was E. Okamoto.<ref>{{Cite journal|last=Okamoto|first=E.|date=1986|title=Proposal for identity-based key distribution systems
==Usage==
Identity-based systems allow any party to generate a public key from a known identity value, such as an ASCII string. A trusted third party, called the private key generator (PKG), generates the corresponding private keys. To operate, the PKG first publishes a master public key, and retains the corresponding '''master private key''' (referred to as ''master key''). Given the master public key, any party can compute a public key corresponding to the identity ''ID'' by combining the master public key with the identity value. To obtain a corresponding private key, the party authorized to use the identity ''ID'' contacts the PKG, which uses the master private key to generate the private key for the identity ''ID''.
==Limitation==
Identity-based systems have a characteristic problem in operation. Suppose Alice and Bob are users of such a system. Since the information needed to find Alice's public key is completely determined by Alice's ID and the master public key, it is not possible to revoke Alice's credentials and issue new credentials without either (a) changing Alice's ID (usually a phone number or an email address which will appear in a corporate directory); or (b) changing the master public key and re-
This limitation may be overcome by including a time component (e.g. the current month) in the identity.{{r|green1}}
==See also==
* [[
* [[Identity-based conditional proxy re-encryption]]
* [[SM9 (cryptography standard)|SM9 - Chinese National Identity Based Cryptography Standard]]
* [[Sakai–Kasahara scheme|Sakai–Kasahara Identity Based Encryption]]
* [[Boneh–Franklin scheme|Boneh–Franklin]]
==References==
{{Reflist}}
{{Cryptography navbox | public-key}}
[[Category:Public-key cryptography]]
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