Modeling computational security in long-lived systems

Ran Canetti, Ling Cheung, Dilsun Kaynar, Nancy Lynch, Olivier Pereira

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


For many cryptographic protocols, security relies on the assumption that adversarial entities have limited computational power. This type of security degrades progressively over the lifetime of a protocol. However, some cryptographic services, such as timestamping services or digital archives, are long-lived in nature; they are expected to be secure and operational for a very long time (i.e. super-polynomial). In such cases, security cannot be guaranteed in the traditional sense: a computationally secure protocol may become insecure if the attacker has a super-polynomial number of interactions with the protocol. This paper proposes a new paradigm for the analysis of long-lived security protocols. We allow entities to be active for a potentially unbounded amount of real time, provided they perform only a polynomial amount of work per unit of real time. Moreover, the space used by these entities is allocated dynamically and must be polynomially bounded. We propose a new notion of long-term implementation, which is an adaptation of computational indistinguishability to the long-lived setting. We show that long-term implementation is preserved under polynomial parallel composition and exponential sequential composition. We illustrate the use of this new paradigm by analyzing some security properties of the long-lived timestamping protocol of Haber and Kamat.

Original languageEnglish
Title of host publicationCONCUR 2008 - Concurrency Theory - 19th International Conference, CONCUR 2008, Proceedings
Number of pages17
StatePublished - 2008
Externally publishedYes
Event19th International Conference on Concurrency Theory, CONCUR 2008 - Toronto, ON, Canada
Duration: 19 Aug 200822 Aug 2008

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume5201 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference19th International Conference on Concurrency Theory, CONCUR 2008
CityToronto, ON


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