1. Long-term cryptographic renewal in time-stamping services and blockchains
- Author
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Meng, Long, Dragan, Constantin-Catalin, and Chen, Liqun
- Abstract
To provide the security of digital data, many applications are using cryptographic algorithms that attackers are infeasible to break since the algorithms are based on hard mathematical problems. However, any single cryptographic algorithm has a limited lifespan due to the limited operational life cycle or increasing computational power of attackers. For many types of digital data, such as identity information, health records, history archives, etc, the security of data needs to be maintained for decades or even permanently, which is much longer than the lifetime of a single cryptographic algorithm. In this PhD thesis, we aim to study the solution for the long-term security of two specific applications: time-stamping services and blockchains, so that their security is not restricted by the lifetime of the underlying cryptographic algorithms. Overall, this thesis is comprised of five papers. The first three papers focus on the long-term security of traditional centralized time-stamping services. In specific, our first work reviews the ISO/IEC standard and discovers several issues that may lead to the failure of designed properties, and we provide a solution to each issue. Since the literature, the ISO/IEC, and ANSI standards only consider the solution of a long-term time-stamping scheme is to renew server-side algorithms, our second work explores a comprehensive long-term time-stamping scheme that addresses the renewal of both client-side hash functions and server-side algorithms. Then we notice that the ISO/IEC and ANSI standards totally specify five types of server-side algorithms, but only the long-term time-stamping schemes based on signatures and hash functions are formally defined and analyzed in the literature. Thus, we fill this gap by formally and analyze the other three types of long-term time-stamping schemes based on MACs, archives, and transient keys respectively as our third paper. The next two papers study the long-term security topic of a blockchain. Based on two existing designs of a long-term secure blockchain scheme, we found that these schemes are not formally analyzed and could be vulnerable to attacks. As one step further, we provide the first security model and construction of a long-term blockchain scheme. Finally, motivated by the decentralized concepts of blockchains, we propose the first long-term timestamping scheme based on a blockchain, which eliminates the trust assumption of a time-stamping authority.
- Published
- 2022
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