'''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.
The first implementation of identity-based signatures and an email-address based [[public-key infrastructure]] ('''PKI''') was developed by [[Adi Shamir]] in 1984,<ref>Adi{{cite Shamir,conference [http|url=https://wwwlink.isecaspringer.orgcom/modulescontent/mydownloadspdf/visit10.php?cid1007/3-540-39568-7_5.pdf |url-status=56&lid=33live |title=Identity-Based Cryptosystems and Signature Schemes]{{Webarchive|first=Adi |last=Shamir |author-link=Adi Shamir |year=1985 |conference=Lecture Notes in Computer Science |editor1-last=Blakley |editor1-first=George Robert |editor2-last=Chaum |editor2-first=David |editor-link1=George Blakley |editor-link2=David Chaum |volume=196 |edition=1 |book-title=Advances in Cryptology Proceedings of CRYPTO '84 |publisher=Springer Berlin Heidelberg |archive-url=https://web.archive.org/web/2020081218583320180726050556/httphttps://wwwlink.isecaspringer.orgcom/modulescontent/mydownloadspdf/visit10.php?cid1007/3-540-39568-7_5.pdf |archive-date=56&lid26 July 2018 |pages=3347-53 |dateisbn=2020978-3-540-0839568-123 }}|doi=10.1007/3-540-39568-7_5 ''Advances|doi-access=free in|access-date=30 CryptologyOctober –2024 Proceedings|language=en of CRYPTO 84, Lecture Notes in Computer Science'', 7:47--53, 1984}}</ref> which allowed users to verify [[digital signatures]] using only public information such as the user's identifier. Under Shamir's scheme, a trusted third party would deliver the private key to the user after verification of the user's identity, with verification essentially the same as that required for issuing a [[public-key certificate|certificate]] in a typical PKI.
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>
