Blockchain-Enabled Secure Logging for Fiscal Electronic Mechanisms: Evaluation of the Greek eSEND and myDATA Tax Systems

Panagiotis Mavridis; Anargyros Baklezos; Christos Nikolopoulos

cs.CRSep 3, 2026

Blockchain-Enabled Secure Logging for Fiscal Electronic Mechanisms: Evaluation of the Greek eSEND and myDATA Tax Systems

Authors: Panagiotis Mavridis, Anargyros Baklezos, Christos Nikolopoulos

Organizations: School of Engineering Dept. of Electronic Engineering Hellenic Mediterranean University Chania, Greece

Abstract

This paper analyzes the implementation of blockchain-based integrity mechanisms in Greek Fiscal Electronic Mechanisms (FEMs) and the central tax information system eSEND. The study examines the cryptographic architecture of fiscal devices, including Electronic Cash Registers, Fiscal Printers, Fiscal Signing Machines, and FEMAS devices, which implement double or triple hash-chain structures to ensure transaction immutability. The transmission protocol between fiscal devices and the central database is also evaluated with respect to encryption, sequential validation, and blockchain verification. In contrast, the architecture of Electronic Invoicing Provider Services and the myDATA central platform is analyzed, highlighting the absence of blockchain-based integrity guarantees. The comparison demonstrates that hardware-based fiscal mechanisms provide stronger guarantees for transaction completeness and tamper resistance than purely software-based invoicing infrastructures. The findings highlight architectural weaknesses in the current e-invoicing framework and propose improvements for ensuring transaction integrity in digital tax ecosystems.

Figures & tables

Fig. 1: A greek restaurant-type Fiscal ECR.

Panel of Figure 2 — Fig. 2: The fiscal memory, an EPROM in resin on the left, and the protection logic on the right.

Fig. 4: The blockchain logic for the double-hash architecture

Table C	Field Length
VAT no. of issuer	(12)
VAT no. of recipient	(12)
Serial Number of FEM	(12)
Additional information	(200)
Date and time (YYYYMMDDHHmm)	(12)
Daily Serial number of sales document	(5)

TABLE I: Table C - transmitted Data Fields to eSEND

Fig. 7: The central information system “eSEND” homepage in 2023.

Fig. 8: Functionality of an Electronic Invoicing Provider Service.

Tamper-Evident Logging

Tamper-evident logging uses cryptographic techniques to make records of actions and events independently verifiable against later alteration.

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Making Duplicate Reimbursement Unrepresentable: A Verified Ethereum E-Invoice System for Humans and AI Agents

Jia Cai

College of Engineering and Computing George Mason UNiversity Fairfax, VA, USA

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Electronic invoices are replacing paper invoices worldwide, but today's centralized architectures leave three problems unsolved on the consumption side: an invoice can be submitted for reimbursement repeatedly, authenticity is difficult for recipients to verify, and data is siloed at a central authority that forms both a performance bottleneck and a single point of failure. This paper presents the design, formal analysis, and implementation of a complete blockchain-based electronic invoice system on Ethereum. We formalize the invoice lifecycle as a guarded labeled transition system and prove, under standard cryptographic and consensus assumptions, that the system guarantees: (i) reimbursement uniqueness--an invoice is reimbursed at most once, even across mutually distrusting organizations; (ii) face integrity--any verified invoice matches the recorded one unless keccak256 second-preimage resistance is broken; and (iii) authorization soundness for every lifecycle operation. The core invariants are machine-checked using Solidity SMTChecker, proving inductive validity across all reachable transaction sequences. The architecture models each invoice as a non-fungible, non-tradable token whose state transitions through five guarded subsystems, employing a lock-based protocol that makes duplicate reimbursement unrepresentable rather than merely detectable. We implement the design as a Solidity 0.8 contract with a four-role web application and evaluate it on a private Ethereum network: issuing costs 646,773 gas, full reimbursement costs under 135,000 gas, all operations run in O(1) time, and a single node sustains 137 issuances/s. Finally, the verified contract serves as a safety envelope for LLM-based reimbursement agents, provably rejecting unsafe actions (duplicate, over-limit, or forged-receipt claims) even when the agent's internal policy fails. All code and benchmarks are open-source.

Abstract

Tamper-Evident Logging

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