Journal:Informatica
Volume 34, Issue 3 (2023), pp. 603–616
Abstract
The article presents the tax declaration scheme using blockchain confidential transactions based on the modified ElGamal encryption providing additively-homomorphic property. Transactions are based on the unspent transactions output (UTxO) paradigm allowing to effectively represent digital asset of cryptocurrencies in e-wallets and to perform financial operations. The main actors around transaction are specified, include money senders, receivers, transaction creator, Audit Authority (AA) and Net of users. A general transaction model with M inputs and N outputs is created, providing transaction amount confidentiality and verifiability for all actors with different levels of available information.
The transaction model allows Net to verify the validity of a transaction, having access only to encrypted transaction data. Each money receiver is able to decrypt and verify the actual sum that is transferred by the sender. AA is provided with actual transaction values and is able to supervise the tax payments for business actors. Such information allows to verify the honesty of transaction data for each user role.
The security analysis of the scheme is presented, referencing to ElGamal security assumptions. The coalition attack is formulated and prevention of this attack is proposed. It is shown that transaction creation is effective and requires almost the same resources as multiple ElGamal encryption. In addition to ElGamal encryption of all income and expenses, an additional exponentiation operation with small exponents, representing transferred sums, is needed. AA computation resources are slightly larger, since they have to be adequate for search procedures in the small range from 1 to ${2^{32}}-1=4294967295$ for individual money transfers.
Pub. online:6 May 2020Type:Research ArticleOpen Access
Journal:Informatica
Volume 31, Issue 2 (2020), pp. 277–298
Abstract
The vulnerable part of communications between user and server is the poor authentication level at the user’s side. For example, in e-banking systems for user authentication are used passwords that can be lost or swindled by a person maliciously impersonating bank.
To increase the security of e-banking system users should be supplied by the elements of public key infrastructure (PKI) but not necessary to the extent of standard requirements which are too complicated for ordinary users.
In this paper, we propose two versions of authenticated key agreement protocol (AKAP) which can be simply realized on the user’s side. AKAP is a collection of cryptographic functions having provable security properties.
It is proved that AKAP1 is secure against active adversary under discrete logarithm assumption when formulated certain conditions hold. AKAP2 provides user’s anonymity against eavesdropping adversary. The partial security of AKAP2 is investigated which relies on the security of asymmetric encryption function.