As a result of high-tech companies such as Google, Yahoo, and Microsoft offering free email services, email has become a primary channel of communication. However, email service providers have traditionally offered little in the way of message privacy protection. This has made emails, of which billions are sent around the world on any day, an attractive data source for personal identity information thieves. Google was one of the first companies to provide substantial email privacy protection when they began using the HTTPS always-on option to encrypt messages sent through their email service, Gmail. Unfortunately, Gmailu27s encryption option does not offer true point-to-point encryption since the encrypted emails are decrypted and stored in plaintext form on Googleu27s servers. This type of approach poses a security vulnerability which is unacceptable to security-minded users such as highly sensitive government agencies and private companies. For these users, true point-to-point encryption is needed. This paper introduces an identity-based one-way group key agreement protocol and describes a point-to-point email encryption scheme based on the protocol. Both the security proofs and the efficiency analysis, with experimental results, of the new scheme are provided.
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