An app signing certificate identifies the key used to sign an Android app. Android uses that identity to verify that an update comes from the same developer as the installed app. In normal updates, the new package must be signed with the matching key; a different certificate generally cannot replace the existing app directly.
This protects app integrity by making unauthorized replacements harder. Attackers may try to work around the check by persuading a user to uninstall a trusted app before installing a modified copy signed with another key. That is different from a routine update and may disrupt the app’s built-in security checks. Install or update banking apps through their official store listing or trusted channel, and treat unexpected requests to remove or reinstall them with caution.