Coffre-fort temporel

There are two natural approaches to implementing timed-release crypto :

1. Use "time-lock puzzles": computational problems that cannot be solved without running a computer continuously for at least a certain amount of time.
2. Use trusted agents who promise not to reveal certain information until a specified date.

Abstract: The notion of "sending a secret message to the future" has been around for over a decade. Despite this, no solution to this problem is in common use, or even attained widespread acceptance as a fundamental cryptographic primitive. We name, construct and specify an implementation for this new cryptographic primitive, "Time-Lapse Cryptography", with which a sender can encrypt a message so that it is guaranteed to be revealed at an exact moment in the future, even if this revelation turns out to be undesirable to the sender. Our solution combines new ideas with Pedersen distributed key generation, Feldman verifiable threshold secret sharing, and El Gamal encryption, all of which rest upon the single, broadly accepted Decisional Diffie-Hellman assumption. We develop a Time-Lapse Cryptography Service ("the Service") based on a network of parties who jointly perform the service. The protocol is practical and secure: at a given time T the Service publishes a public key so that anyone can use it, even anonymously. Senders encrypt their messages with this public key whose private key is not known to anyone - not even a trusted third party - until a predefined and specific future time T + at which point the private key is constructed and published. At or after that time, anyone can decrypt the ciphertext using this private key. The Service is envisioned as a public utility publishing a continuous stream of encryption keys and subsequent corresponding time-lapse decryption keys. We complement our theoretical foundation with descriptions of specific attacks and defenses, and describe important applications of our service in sealed bid auctions, insider stock sales, clinical trials, and electronic voting.

Abstract. Timed-release encryption (TRE) is a two-factor encryption scheme combining public key encryption and time-dependent encryption- decryption requires a trapdoor which is kept confidential by a timeserver until at an appointed time. This paper revisits two recent results. In ESORICS 2007, Chalkias et al. proposed an efficient anonymous TRE scheme. Unfortunately, we show the security threats of their scheme in the presence of a curious time-server and an impatient recipient. Recently, Chow et al. proposed an encryption scheme in the standard model which can be used as TRE. Nevertheless, only confidentiality is guaranteed. We demonstrate how to support pre-open capability, which is often desirable in applications of TRE. Our extension also enables only the recipient to know the release-time from the ciphertext. This feature is not considered in previous notion of release-time confidentiality.

Résumé

Le voyage dans le temps a toujours été un sujet fascinant, que ce soit en littérature ou en physique. De même, en cryptographie, nous nous demandons comment conserver des données confidentielles pendant un certain temps. Dans cette thèse, nous étudions comment faire voyager des informations privées vers le futur. Ce travail est divisé en trois parties :

1. le chiffrement temporisé (timed-release encryption),
2. le chiffrement de témoin (witness encryption)
3. et l'auto-chiffrement (self-encryption).

...

Voici une référence d'un article basé sur une publication de 2015 :

• How To Create Time-locked Transactions with Bitcoin

Et quelques autres articles :

• How to build time-lock encryption Jia Liu · Tibor Jager · Saqib A. Kakvi · Bogdan Warinschi Received: 21 February 2017 / Revised: 19 January 2018 / Accepted: 20 January 2018
• Practical Time-Release Blockchain Sang-Wuk Chae, Jae-Ik Kim and Yongsu Park / 2020