Fountain codes in censorship circumvention rendezvous
Authors: Eleanor Cawthon (University of California, Berkeley), David Fifield
Year: 2026
Issue: 2
Pages: 7–11
Abstract: Censorship circumvention protocols often require a rendezvous step to exchange information needed to set up a connection. We investigate the potential of fountain codes, also known as rateless erasure codes, for this purpose. Fountain codes reliably transmit a message by breaking it into many small, specially encoded pieces. Taking inspiration from how they are used in the Collage and Assemblage circumvention systems, we narrow our focus to rendezvous, and consider the usefulness of fountain codes as a design component in themselves, not necessarily adjunct to steganography. Our specific motivation is to enable rendezvous over encrypted DNS, which has attractive anti-blocking properties, but is difficult to use for generic data exchange. Fountain codes offer an uncomplicated way to send discrete, bounded-length messages over covert channels that, like DNS, may convey only small amounts of data at a time, or are unordered or unreliable. We provide a proof-of-concept implementation over UDP that demonstrates the essential elements of fountain code–based rendezvous: breaking a message into pieces, transmitting them over a lossy channel, and reconstructing them at the other end. We work out a prospective design for rendezvous over encrypted DNS, and comment on design considerations in general.
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