Application Signing

All Android applications (.apk files) must be signed with a certificate whose private key is held by their developer. This certificate identifies the author of the application. The certificate does not need to be signed by a certificate authority: it is perfectly allowable, and typical, for Android applications to use self-signed certificates. The certificate is used only to establish trust relationships between applications, not for wholesale control over whether an application can be installed. The most significant ways that signatures impact security is by determining who can access signature-based permissions and who can share user IDs.