It is the keystore of java, which is used for communication encryption, such as digital signature. The Keystore is used to store key pairs, such as public key and private key. Generally speaking, this thing establishes the connection between the developer and the app, and you are its creator, so you have absolute control over this apk. We can usually do this with this key:

1. You can get some different permissions by using a special key signature.

2. If 2. APK is signed by one key, and files signed by another key will not be able to install or overwrite the old version when published, which can prevent the application you installed from being overwritten or replaced by malicious third parties.