The steps Chris would take, after creating the HighScore and HighScorePermission classes, are:
javac HighScore*.java -d .
jar cvf hs.jar com/scoredev/scores/HighScore*.class
keytool -genkey -keystore chris.keystore -alias signJars
Specify whatever you want for the passwords and distinguished name information.
jarsigner -keystore chris.keystore hs.jar signJars
keytool -export -keystore chris.keystore
-alias signJars -file Chris.cer
That is, supply them
hs.jar,Chris.cer, andHighScore and HighScorePermission classes must be granted in a policy file in order to work. For this, Chris could supply the exact grant entry needed.