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

摘要： X.509证书是安全套接层（Secure Sockets Layer，SSL）/ 传输层安全（Transport Layer Security，TLS）协议族中实现身份认证和信任建立的关键基础，其解析与验证行为的正确性直接影响协议的安全性。然而，不同TLS实现之间在证书处理流程上存在差异，容易导致语义偏差、安全绕过，甚至漏洞利用问题。现有差分测试方法多聚焦于解析或验证的单阶段测试，且普遍忽略字段之间的语义关联，存在缺陷成因分析不够全面、字段覆盖范围有限等不足。为此，本文提出一种基于模板驱动的证书解析与验证差分测试方法。该方法结合X.509证书的RFC标准构建通用证书模板类，对字段结构、取值约束和变异操作进行程序化建模，通过差异向量反馈机制捕获实现差异，结合字段关联关系制定联合变异策略，构建完整的迭代测试框架。在四种主流TLS实现上开展实验评估，构造近250份测试证书样本，成功触发133个解析与验证阶段的差异行为，最终分析得到9个合规性实现缺陷。

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