A long standing problems is how a participant who owns a secret can release some document such that at a predefined time in the future, people can extract the secret from the document, but not before. We review the proposed approaches (including with smart contracts) which are not fully satisfactory. One interesting approach is based on the notion of witness encryption and blockchains. However, existing witness encryption schemes are inefficient. We show how to build a new (and efficient) one and estimate the complexity to send a secret in the future.

Bio:Serge Vaudenay entered at the Ecole Normale Supérieure in Paris in 1989 with a major in mathematics. He received his PhD in computer sciences from University of Paris 7 - Denis Diderot in 1995. He subsequently became a research fellow at CNRS (National Center for Scientific Research in France). In 1999, he was appointed as a Professor at the EPFL, where he created the Security and Cryptography Laboratory. He works on cryptography and the security of digital information. Most of his work relates to security analysis and provable security of cryptographic algorithms and protocols, specially in secure communication, post-quantum cryptography, RFID protocols and distance bounding. Recently, he joined the GlobalID company where he develops secure privacy-preserving applications based on biometry.