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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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|first = Cliff
|title = Cryptography and Coding
|volume = 2260/2001
|pages = 360–363
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|publisher = Springer
|doi = 10.1007/3-540-45325-3_32
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}}</ref><ref>{{cite web|archive-url=https://web.archive.org/web/20150627063023/http://www.bristol.ac.uk/pace/graduation/honorary-degrees/hondeg08/cocks.html|archive-date=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|journal=Electronics Letters|volume=22|issue=24|pages=1283–1284|doi=10.1049/el:19860880|bibcode=1986ElL....22.1283O|issn=0013-5194}}</ref> Identity based key agreement schemes also allow for "escrow free" identity based cryptography. A notable example of such an escrow free identity based key agreement is the McCullagh-Barreto's "Authenticated Key Agreement without Escrow" found in section 4 of their 2004 paper, "A New Two-Party Identity-Based Authenticated Key Agreement".<ref>{{Cite
==Usage==
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==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-issuing private keys to all users, including Bob.<ref name=green1>{{Cite book
This limitation may be overcome by including a time component (e.g. the current month) in the identity.{{r|green1}}
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