To retrieve your Google Play Public Key, simply navigate to the following URL (or click on the image) and login using your developer details:
Once logged in, click the app for which you require the Public Key, and then select Services & API's from the left hand menu:
Here you can find the Public Key for your application:
Should you need to implement this into YUDU Publisher (usually this process is done during the application build process), copy your Public Key, navigate to your Group node on YUDU Publisher (the node containing your publications) and click edit next to the name of the Group node in the top left:
From here to the right of the screen, enter your Public Key and hit Submit at the bottom of the screen to confirm your changes.