This document defines Secure/Multipurpose Internet Mail Extensions (S/MIME) version 3.2. S/MIME provides a consistent way to send and receive secure MIME data. Digital signatures provide authentication, message integrity, and non-repudiation with proof of origin. Encryption provides data confidentiality. Compression can be used to reduce data size. This document obsoletes RFC 3851. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by

Abstract. Anonymous communications provides an important privacy service by keeping passive eavesdroppers from linking communicating parties. However, using long-term statistical analysis of traffic sent to and from such a system, it is possible to link senders with their receivers. Cover traffic is an effective, but somewhat limited, counter strategy against this attack. Earlier work in this area proposes that privacysensitive users generate and send cover traffic to the system. However, users are not online all the time and cannot be expected to send consistent levels of cover traffic, drastically reducing the impact of cover traffic. We propose that the mix generate cover traffic that mimics the sending patterns of users in the system. This receiver-bound cover helps to make up for users that aren’t there, confusing the attacker. We show through simulation how this makes it difficult for an attacker to discern cover from real traffic and perform attacks based on statistical analysis. Our results show that receiver-bound cover substantially increases the time required for these attacks to succeed. When our approach is used in combination with user-generated cover traffic, the attack takes a very long time to succeed. Key words: privacy-enhancing technologies, cover traffic, anonymity 1

Abstract- Wireless Internet roaming may include several radio access networks involving different layer 2 technologies such as 802.11b, CDMA and GPRS. As a mobile user moves around and switches between wireless cells, subnets and domains, it needs to maintain the session continuity. At the same time security of signaling and transport media should not be compromised. A multi-layer security framework involving user authentication, packet based encryption and access control mechanism can provide the desired level of security to the mobile users. Architecture, implementation and performance of a similar framework in a mobile environment is presented here. Results and performance analysis of the implementation will be of immense value for wireless Internet service providers, before it is actually deployed in a wide scale manner.

This paper examines how the Internet's e-mail infrastructure should evolve to better support continuous media (CM) e-mail, such as audio and video. We assert that the problem is not simply a matter of adding the obvious new functionality to user agents (mail readers), such as audio and video capture, but requires the adoption of a new delivery model. We do this by examining the problems that arise using current methods to deliver video messages, and we show how senderside storage and media streaming solve these problems. Finally, we describe an implementation strategy that requires changes only to individual sender systems, but enables CM e-mail to be delivered universally to any recipient, thus providing a realistic evolutionary path that can be adopted incrementally by individual mail systems.