Certificate transparency for web and mobile apps

What this post added

Introduces Certificate Transparency (CT) as a security measure against mis-issued certificates. Explains the underlying Merkle Tree data structure used in CT logs. Provides guidance for web app developers on verifying CT compliance using browser developer tools. For mobile app developers, it details client-side CT checks, including specific instructions for iOS (Info.plist modification for older versions) and Android (using the `certificate-transparency-android` library with OkHttpClient). It also emphasizes the server-side requirement of a valid Server Certificate Timestamp (SCT).