A Non-repudiable Protocol for Secure Messaging

As Oppliger stated in [1], secure messaging refers to the ability to provide data confidentiality, data integrity, data origin authentication, and nonrepudiation of origin services for email. It's very important but poorly developed and has very limited application. We propose an email protocol assures non-repudiability which means that if the email is successfully sent, the sender cannot deny s/he has actually sent the mail and the recipient cannot deny s/he has actually received it. The protocol uses an efficient RSA-based convertible signature.