Abstract
This paper studies known indexing structures from a new point of view: minimisation of data exchange between an IoT device acting as a blockchain client and the blockchain server running a protocol suite that includes two Guy Fawkes protocols, PLS and SLVP. The PLS blockchain is not a cryptocurrency instrument; it is an immutable ledger offering guaranteed non-repudiation to low-power clients without use of public key crypto. The novelty of the situation is in the fact that every PLS client has to obtain a proof of absence in all blocks of the chain to which its counterparty does not contribute, and we show that it is possible without traversing the block’s Merkle tree. We obtain weight statistics of a leaf path on a sparse Merkle tree theoretically, as our ground case. Using the theory we quantify the communication cost of a client interacting with the blockchain. We show that large savings can be achieved by providing a bitmap index of the tree compressed using Tunstall’s method. We further show that even in the case of correlated access, as in two IoT devices posting messages for each other in consecutive blocks, it is possible to prevent compression degradation by re-randomising the IDs using a pseudorandom bijective function. We propose a low-cost function of this kind and evaluate its quality by simulation, using the avalanche criterion.
Highlights
This paper gives statistical analysis of some known data structures required for the implementation of the PLS blockhain (Shafarenko 2021) or PLSB for short, whose purpose is to support a swarm of IoT devices, or things operating on the premises of a single administrative authority, for example a smart hospital
The path weight was quantified in terms of the number of adjunct hashes required for its leaf proof
We determined that the mean path weight of a sparse MT tree is close to that of a dense, truncated MT tree, with the latter being slightly better at most leaf-probability values p in the practically interesting interval
Summary
This paper gives statistical analysis of some known data structures required for the implementation of the PLS (permissioned) blockhain (Shafarenko 2021) or PLSB for short, whose purpose is to support a swarm of IoT devices, or things operating on the premises of a single administrative authority, for example a smart hospital. The use of a blockchain is for the purposes of audit trail, authentication and non-repudiation of all actors, both human and unmanned, including small, bare-metal microcontrollers that supply critical sensor data and those which drive actuators. Typically messages are not transactions in the financial sense, so checks such as double spending are not relevant; value checks are domain-specific and are best performed by smart contracts, which leaves the authenticity and provenance of each message posted on the ledger as the only general validity concerns. The PLS blockchain (Shafarenko 2021) assures (ii) by employing Guy-Fawkes Protocols (GFPs) (Anderson et al 1998)
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