SSL has become a key tool in securing IT infrastructures. Because SSL certificates are valid only for the time they specify, monitoring the certificates becomes an important part of app management. A Symantec white paper entitled SSL for Apps: Best Practices for Developers (pdf) outlines the steps required to secure your apps using SSL/TLS.
When establishing an SSL connection, the server returns one or more certificates to create a "chain of trust." The certificates may not be received in a predictable order. Also, the server may return more than necessary or require that the client look for necessary certificates elsewhere. In the latter case, a certificate with a caIssuers entry in its authorityInfoAccess extension will list a protocol and extension for the issuing certificate.
Once you've determined the end-entity SSL certificate, you verify that the chain from the end-entity certificate to the trusted root certificate or intermediate certificate is valid.
To help developers ensure their apps are protected against man-in-the-middle attacks resulting from corrupted SSL certificates, Google recently released a tool called nogotofail. As PC World's Lucian Constantin explains in a November 4, 2014, article, apps become vulnerable to such attacks because of bad client configurations or unpatched libraries that may override secure default settings.
Nogotofail simulates man-in-the-middle attacks using deep packet inspection to track all SSL/TLS traffic rather than monitoring only the two ports usually associated with secure connections, such as port 443. The tool can be deployed as a router, VPN server, or network proxy.