Inspecting application certificates and signatures

Application certificates are what developers use to declare their trust in the applications they publish to the application market. This is done by declaring their identities and associating them to their application(s) cryptographically. Application signatures make sure that no application can impersonate another by providing a simple and effective mechanism to determine and enforce the integrity of Android applications. It is a requirement that all applications be signed with certificates before they are installed.

Android application signing is a repurposing of JAR signing. It works by applying a cryptographic hash function to an application's contents. We will soon see exactly which of the contents in the APK files are hashed. The hashes are then distributed with a certificate that declares the developer's identity, associating it to the developer's public key and effectively, his/her private key, since they are related...