Abstract
Electronic mail, e-mail in short, has been used to transfer various types of electronic data on internet. In order to deliver the e-mail from the sender to the receiver both efficiently and securely, the e-mail system usually employs both conventional and public key cryptographic systems. The basic protection in an e-mail system is to encrypt the bulk mail using a conventional cryptosystem with a short-term key and to protect the short-term key using a public-key cryptosystem with the receiver's public key. However this protection cannot provide perfect forward secrecy because once the receiver's secret key is disclosed, all previous used short-term keys will also be opened and hence all previous e-mails will be learned. Two new e-mail protocols providing perfect forward secrecy are proposed in this paper. © 2005 IEEE.