History-based signature or how to trust anonymous documents

This paper tackles the following problem: how to decide whether data are trustworthy when their originator wants to remain anonymous? More and more documents are available digitally and it is necessary to have information about their author in order to evaluate the accuracy of those data. Digital signatures and identity certificates are generally used for this purpose. However, trust is not always about identity. In addition authors often want to remain anonymous in order to protect their privacy. This makes common signature schemes unsuitable. We suggest an extension of group signatures where some anonymous person can sign a document as a friend of Alice, as a French citizen, or as someone that was in Paris in December, without revealing any identity. We refer to such scheme as history-based signatures.