Cryptanalysis of the RSA-CEGD protocol

TL;DR

This paper critically analyzes the RSA-CEGD protocol for e-goods delivery, revealing a significant fairness flaw through a severe attack and highlighting additional vulnerabilities.

Contribution

It provides the first cryptanalysis showing that RSA-CEGD fails to ensure fairness, exposing critical security weaknesses in the protocol.

Findings

RSA-CEGD protocol is not fair due to a specific attack

The protocol has vulnerabilities beyond fairness issues

The analysis questions the security assumptions of RSA-CEGD

Abstract

Recently, Nenadi\'c et al. (2004) proposed the RSA-CEGD protocol for certified delivery of e-goods. This is a relatively complex scheme based on verifiable and recoverable encrypted signatures (VRES) to guarantee properties such as strong fairness and non-repudiation, among others. In this paper, we demonstrate how this protocol cannot achieve fairness by presenting a severe attack and also pointing out some other weaknesses.