Security analysis of two lightweight certificateless signature schemes

TL;DR

This paper critically examines two lightweight certificateless signature schemes designed for IoT and HWSN, revealing vulnerabilities that allow for easy forgery despite claims of unforgeability.

Contribution

It provides the first security analysis showing that both schemes can be forged, challenging their claimed security properties.

Findings

Karati et al.'s scheme is vulnerable to Type 1 adversaries forging signatures.

Kumar et al.'s scheme is vulnerable to both Type 1 and Type 2 adversaries.

Both schemes can be compromised to forge signatures on arbitrary messages.

Abstract

Certificateless cryptography can be considered as an intermediate solution to overcome the issues in traditional public key infrastructure (PKI) and identity-based public key cryptography (ID-PKC). There exist a vast number of certificateless signature (CLS) schemes in the literature; however, most of them are not efficient enough to be utilized in limited resources environments such as Internet of things (IoT) or Healthcare Wireless Sensor Networks (HWSN). Recently, two lightweight CLS schemes have been proposed by Karati et al. and Kumar et al. to be employed in IoT and HWSNs, respectively. While both schemes are claimed to be existentially unforgeable, in this paper, we show that both these signatures can easily be forged. More specifically, it is shown that 1) in Karati et al.'s scheme, a type 1 adversary, considered in certificateless cryptography, can generate a valid partial private key corresponding to any user of its choice and as a consequence, it can forge any users' signature on any message of its choice, and 2) in Kumar et al.'s scheme, both types of adversaries which are considered in certificateless cryptography are able to forge any signer's signature on an arbitrary message.