Worked on the openssl/openssl repository to address a regression in the x509 -checkend functionality, focusing on stabilizing certificate expiry checks and extending support for multi-certificate scenarios. Applied C programming and Perl scripting to implement the fix, update documentation, and expand unit tests, ensuring robust test coverage and clear usage guidance. Collaborated closely with peers through code reviews and merging processes, emphasizing code quality and maintainability. This work reduced operational risk by improving the reliability of automated certificate checks, with all changes thoroughly documented and tested. The approach demonstrated attention to detail in both technical implementation and collaborative development practices.