The goal of the Whisper project is to build an easy-to-use, infrastructureless, reliable, secure, private communication system. This system aims to resist surveillance, censorship, propaganda, and reprisal by providing anonymity, privacy, confidentiality, deniability, robustness, and good performance. We pay particular attention to designing protocols that do not rely on centralized control points that may be vulnerable to attack. Our system is designed to be suitable for use by people without special training.

The Internet is often credited with broadening the ability to access and share information. Comparing the global impact of the Internet with that of the Gutenberg press during their first 35 years of existence confirms its importance. Already, traditional and centralized sources of information are losing markets to both formal (e.g., news websites) and informal (e.g., personal friends-and-family mailing lists and blogs) decentralized sources of information that use the Internet for distribution. However, the Internet has characteristics that can undermine privacy and freedom of speech. A largely-static infrastructure that channels the majority of traffic through a limited number of locations eases surveillance and censorship.

As illustrated in the above figure, the system has three layers, (1) application, (2) secure transport, and (3) network. The target application is low-bandwidth and delay-tolerant text-based communication, e.g., email and text messaging. The secure transport layer provides confidential and anonymous host-to-host delivery using mix-chains. The reply blocks constructed by a host and shared during face-to-face contact act as the transport layer addresses. The network layer delivers messages between mix-nodes using geographic routing. A network address is a two-tuple containing a pseudonym and location. Keys for encryption are exchanged face-to-face between contacts, so no public key infrastructure is required.