The most detailed view of the apk signature information

First you need a java environment, or you have installed Android Studio.
Just download an apk with your mobile phone, here I use the apk of QQ, and then send the apk to the computer.
Next, change the .apk suffix to .zip, as shown in the figure below.

Then it is super simple to decompress, and then you can see as shown in the figure below. The most important thing here is the META-INF folder. Open

this folder , we can see that there is a .RSA file

win+R, enter cmd

to enter the META-INF folder just now, enter the command line
keytool -printcert -file xxx.RSA (I am ANDROIDR.RSA here), you can see To the following signature information.

Check whether the apk is signed successfully, and
the following information appears through the command jarsigner -verify xx.apk (jarsigner -verify QQ.apk), indicating that it has been signed.