Generic Authenticated Data Structures, Formally

Authenticated data structures are a technique for outsourcing data storage and maintenance to an untrusted server. The server is required to produce an efficiently checkable and cryptographically secure proof that it carried out precisely the requested computation. Recently, Miller et al. [https://doi.org/10.1145/2535838.2535851] demonstrated how to support a wide range of such data structures by integrating an authentication construct as a first class citizen in a functional programming language. In this paper, we put this work to the test of formalization in the Isabelle proof assistant. With Isabelle\u27s help, we uncover and repair several mistakes and modify the small-step semantics to perform call-by-value evaluation rather than requiring terms to be in administrative normal form

Authenticated Data Structures as Functors in Isabelle/HOL

Merkle trees are ubiquitous in blockchains and other distributed ledger technologies (DLTs). They guarantee that the involved systems are referring to the same binary tree, even if each of them knows only the cryptographic hash of the root. Inclusion proofs allow knowledgeable systems to share subtrees with other systems and the latter can verify the subtrees\u27 authenticity. Often, blockchains and DLTs use data structures more complicated than binary trees; authenticated data structures generalize Merkle trees to such structures. We show how to formally define and reason about authenticated data structures, their inclusion proofs, and operations thereon as datatypes in Isabelle/HOL. The construction lives in the symbolic model, i.e., we assume that no hash collisions occur. Our approach is modular and allows us to construct complicated trees from reusable building blocks, which we call Merkle functors. Merkle functors include sums, products, and function spaces and are closed under composition and least fixpoints. As a practical application, we model the hierarchical transactions of Canton, a practical interoperability protocol for distributed ledgers, as authenticated data structures. This is a first step towards formalizing the Canton protocol and verifying its integrity and security guarantees

Improved authenticated data structures for blockchain synchronization

One of the most important components in a public blockchain like Bitcoin and Ethereum is the authenticated data structure that keeps track of all block data, transactions, and the world state (account balance, smart contract states, etc.) Thanks to authenticated data structures, lightweight nodes only need to store authentication information and can delegate queries to those nodes with a full replica of data and the authenticated data structure. The lightweight nodes can trust the query results after verifying against the authentication information. It is also critical to have enough nodes in the network that are equipped with the authenticated data structure to ensure scalability and availability, which is especially important for public blockchains. Therefore, every public blockchain highly encourages users to download the authenticated data structure as the first step. Fetching all elements from the entire authenticated data structure is a novel query type that has not gathered attention in the past. We describe this new emerging query type in the three-party authenticated data structure (ADS). We improve the design and implementation of the authenticated data structure so that the new query type is well-supported. We specifically apply the improvements to the Ethereum blockchain network. With our proposed ADS system in Ethereum, we improve Ethereum state synchronization performance by 216 times

Database Outsourcing with Hierarchical Authenticated Data Structures

In an outsourced database scheme, the data owner delegates the data management tasks to a remote service provider. At a later time, the remote service is supposed to answer any query on the database. The essential requirements are ensuring the data integrity and authenticity with efficient mechanisms. Current approaches employ authenticated data structures to store security information, generated by the client and used by the server, to compute proofs that show the answers to the queries are authentic. The existing solutions have shortcomings with multi-clause queries and duplicate values in a column. We propose a hierarchical authenticated data structure for storing security information, which alleviates the mentioned problems. Our solution handles many different types of queries, including multi-clause selection and join queries, in a dynamic database. We provide a unified formal definition of a secure outsourced database scheme, and prove that our proposed scheme is secure according to this definition, which captures previously separate properties such as correctness, completeness, and freshness. The performance evaluation based on our prototype implementation confirms the efficiency of our proposed scheme, showing about 3x to 5x enhancement in proof size and proof generation time in comparison to previous work, and about only 4% communication overhead compared to the actual query result in a real university database

A Blockchain-Assisted Hash-Based Signature Scheme

We present a server-supported, hash-based digital signature scheme. To achieve greater efficiency than current state of the art, we relax the security model somewhat. We postulate a set of design requirements, discuss some approaches and their practicality, and finally reach a forward-secure scheme with only modest trust assumptions, achieved by employing the concepts of authenticated data structures and blockchains. The concepts of blockchain authenticated data structures and the presented blockchain design could have independent value and are worth further research