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Encoding for Censorship-Resistant Sharing (ECRS)

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When GNUnet shares files, it uses a content encoding that is called ECRS, the Encoding for Censorship-Resistant Sharing. Most of ECRS is described in the (so far unpublished) research paper attached to this page. ECRS obsoletes the previous ESED and ESED II encodings which were used in GNUnet before version 0.7.0.

The rest of this page assumes that the reader is familiar with the attached paper. What follows is a description of some minor extensions that GNUnet makes over what is described in the paper. The reason why these extensions are not in the paper is that we felt that they were obvious or trivial extensions to the original scheme and thus did not warrant space in the research report.

Namespace Advertisements

An SBlock with identifier ′all zeros′ is a signed advertisement for a namespace. This special SBlock contains metadata describing the content of the namespace. Instead of the name of the identifier for a potential update, it contains the identifier for the root of the namespace. The URI should always be empty. The SBlock is signed with the content provder′s RSA private key (just like any other SBlock). Peers can search for SBlocks in order to find out more about a namespace.


GNUnet implements KSBlocks which are KBlocks that, instead of encrypting a CHK and metadata, encrypt an SBlock instead. In other words, KSBlocks enable GNUnet to find SBlocks using the global keyword search. Usually the encrypted SBlock is a namespace advertisement. The rationale behind KSBlocks and SBlocks is to enable peers to discover namespaces via keyword searches, and, to associate useful information with namespaces. When GNUnet finds KSBlocks during a normal keyword search, it adds the information to an internal list of discovered namespaces. Users looking for interesting namespaces can then inspect this list, reducing the need for out-of-band discovery of namespaces. Naturally, namespaces (or more specifically, namespace advertisements) can also be referenced from directories, but KSBlocks should make it easier to advertise namespaces for the owner of the pseudonym since they eliminate the need to first create a directory.

Collections are also advertised using KSBlocks.

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