How do I sign a Java applet for use in a browser?

Question

I\'m trying to deploy a Java applet on my website. I also need to sign it, because I need to access the clipboard. I\'ve followed all the signing tutorials I could find bu

Answer 1

Edit: This answer is historical. JDK9 will apparently deprecate applets. At the time of writing (1 Jan 2017), you should sign applets but give them no additional privileges, then transition to a more current technology.

I suggest that you don't sign the code. If you're playing about with other people's security, then you really should know what you are doing.

JTextComponent should allow copy and paste of text, if that is sufficient.

jarsigner -verify will check that your jar is signed. You can also have a quick look at the manifest file and files within META-INF/.

The pop up dialog to trust certificates may be disabled. In Sun's implementation: open the Java Control Panel; go to the Advanced tab; expand the Security node; the top two tickboxes should be "Allow user to grant permissions to signed context" and "Allow user to grant permissions to content from an untrusted authority".

Answer 2

Perhaps it's because you're opening some .class files outside the jar file?

That way it may not display the warning. I tried doing it that way but it still showed me the certificate warning and for a simple case it actually prevented me from accessing a class from the JAR with the separated class.

Maybe your specific setup or file organization causes that behavior. If you can layout that in more detail we could help better (or rather, try putting all those .class files in yet another signed Jar and add it to the archive"..., anotherJar.jar").

Answer 3

First, I'd suggest getting a valid code signing certificate. You can get a free cert from Thawte. Although generally these certs are used for S/MIME, they are also valid for code signing.

The second option is to import your self signed cert into the cacert file of the JRE which your browser is invoking.

The next thing to check is to make sure your browser is running your latest jar. One way to do this is to always increment your version number. The other option is for you to clear your Java applet cache. I usually clear my browser's cache as well, but this shouldn't be needed.

Answer 4

You mentioned:

When I open that html file, I never get the security confirmation dialog box...

Are you opening the file from your local file system, or via a URL to a web server hosting the HTML file and applet jar(s)? That could be why you get no warning.

Answer 5

3 easy steps

1. keytool -genkey -keystore myKeyStore -alias me

2. keytool -selfcert -keystore myKeyStore -alias me

3. jarsigner -keystore myKeyStore jarfile.jar me

Answer 6

Here is a way to sign your jars and then check to see that all the class files are signed with your keystore.

#!/bin/bash
KEYSTORE=/home/user/NetBeansProjects/sign/keystore
FILES=`find /home/user/NetBeansProjects/Project/dist/ -name "*.jar"`
for f in $FILES; 
   do echo password |  /usr/bin/jarsigner -keystore $KEYSTORE -verbose $f myself;
   echo "Signed $f"; 
  /usr/bin/jarsigner -verify -verbose -certs $f | grep X.509 | sort -u;
done