关键词: 差分测试, X.509证书, TLS实现, 解析与验证, 缺陷检测

Abstract: X.509 certificates constitute the fundamental basis for identity authentication and trust establishment within the Secure Sockets Layer(SSL)/Transport Layer Security(TLS) protocol. The accuracy of their parsing and verification behaviors directly determines the security of the protocol. However, discrepancies exist in certificate processing procedures across different TLS implementations, which can readily lead to semantic deviations, security bypasses, and even vulnerability exploitation. Existing differential testing methodologies predominantly focus on single-stage assessments of either parsing or verification, frequently overlooking the semantic associations between certificate fields. This oversight results in incomplete analysis of defect root causes and yields limited inter-field coverage. Consequently, this paper proposes a template-driven differential testing method for certificate parsing and verification. This approach integrates the RFC standard for X.509 certificates to construct a general certificate template class, programmatically models field structures, value constraints, and mutation operations, captures implementation differences via a differential vector feedback mechanism, and formulates joint mutation strategies based on field associations. These elements collectively establish a comprehensive iterative testing framework. Experimental evaluations conducted on four mainstream TLS implementations involved the construction of nearly 250 test certificate samples. These successfully triggered 133 differential behaviors during parsing and verification stages, ultimately identifying 9 compliance implementation defects.

Key words: differential testing, X.509 certificate, TLS implementation, parsing and validation, flaw detection