Identity-based encryption: Difference between revisions

Revision as of 21:47, 19 April 2006

Revision as of 22:03, 30 May 2006

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==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. Given the master public key, any party can compute a public key corresponding to the identity ''Ii'' by combining the master public key with the identity value. To obtain a corresponding private key, the party authorized to use the identity ''Ii'' contacts the PKG, which uses the master private key to generate the private key for identity ''Ii''.

As a result, parties may encrypt messages (or verify signatures) with no prior distribution of keys between individual participants. This is extremely useful in cases where pre-distribution of authenticated keys is inconvenient or infeasable due to technical restraints. However, to decrypt or sign messages, the authorized user must obtain the appropriate private key from the PKG. A caveat of this approach is that the PKG must be highly trusted, as it is capable of generating any user's private key and may therefore decrypt (or sign) messages without authorization. Because any user's private key can be generated through the use of the third party's secret, this system has inherent [[key escrow]]. A number of variant systems have been proposed which remove the escrow including [[certificate-based encryption]], [[secure key issuing cryptography]] and [[certificateless cryptography]].