How to Sign Applets Using RSA Certificates

Since Java Plugin 1.2.2, RSA signed applets have been supported to make deploying signed applets much easier. However, signing applets through RSA is still difficult for most novice applet developers, and prevents them from fully taking advantage of this feature of Java Plug-in. This document provides step-by-step instructions for signing applets using RSA certificates, so novice applet developers will be able to sign their applets in Java Plug-in without fully understanding all the complex security related terminology.

To sign an applet, several things are needed:

1. Signing tools.
2. An RSA keypair and a certificate chain for the public keys.
3. The applet itself and all its class files, bundled as JAR files.

Signing tools

Two types of signing tools are currently supported in Java Plug-in to sign RSA applets:

1. Jarsigner -- a tool that is shipped as part of the Java 2 Software Development Kit.
   
2. Netscape Signing Tool -- a tool that is provided by Netscape for signing applets in Navigator/Communicator. The latest version of the signing tool may be download from http://developer.netscape.com/software/signedobj/jarpack.html. Please notice that Netscape no longer makes older version of the signing tool available for download.

RSA certificates

RSA certificates may be purchased from a Certificate Authority (CA) that supports RSA, such as VeriSign and Thawte. Some CAs (such as VeriSign) implement different protocols for issuing certificates, depending on the particular signing tool you are using.

Jarsigner

At the time this document was written, we have demonstrated interoperability of Jarsigner with VeriSign and Thawte. To use jarsigner to sign applets using RSA certificates, obtain the Sun Java Signing certificate from VeriSign, or Java Code Signing certificate from Thawte, or a similar certificate from other CAs. During the process of certificate enrollment, you will be asked to provide the certificate signing request (CSR). To generate the CSR, follow these steps:

1. Use keytool to generate an RSA keypair (using the "-genkey -keyalg rsa" options). Make sure your distinguished name contains all the components mandated by VeriSign/Thawte. e.g.

   C:\>C:\jdk1.3\bin\keytool -genkey -keyalg rsa -alias MyCert Enter keystore password: ********* What is your first and last name? [Unknown]: XXXXXXX YYY What is the name of your organizational unit? [Unknown]: Java Software What is the name of your organization? [Unknown]: Sun Microsystems What is the name of your City or Locality? [Unknown]: Cupertino What is the name of your State or Province? [Unknown]: CA What is the two-letter country code for this unit? [Unknown]: US Is <CN=XXXXXXX YYY, OU=Java Software, O=Sun Microsystems, L=Cupertino, ST=CA, C=US> correct? [no]: yes Enter key password for <MyCert> (RETURN if same as keystore password): *********

   
   
2. Use "keytool -certreq" to generate a certification signing request. Copy the result and paste it into the VeriSign/Thawte webform. For example, 

   C:\>C:\jdk1.3\bin\keytool -certreq -alias MyCert Enter keystore password:  ********* -----BEGIN NEW CERTIFICATE REQUEST----- MIIBtjCCAR8CAQAwdjELMAkGA1UEBhMCVVMxCzAJBgNVBAgTAkNBMRIwE AYDVQQHEwlDdXBlcnRpbm8xGTAXBgNVBAoTEFN1biBNaWNyb3N5c3RlbX MxFjAUBgNVBAsTDUphdmEgU29mdHdhcmUxEzARBgNVBAMTClN0YW5sZXk gSG8wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBALTgU8PovA4y59eb oPjY65BwCSc/zPqtOZKJlaW4WP+UhmebE+T2Mho7P5zXjGf7elo3tV5uI 3vzgGfnhgpf73EoMow8EJhly4w/YsXKqeJEqqvNogzAD+qUv7Ld6dLOv0 CO5qvpmBAO6mfaI1XAgx/4xU/6009jVQe0TgIoocB5AgMBAAGgADANBgk qhkiG9w0BAQQFAAOBgQAWmLrkifKiUYtd4ykhBtPWSwW/IKkgyfIuNMML dF1DH8neSnXf3ZLI32f2yXvs7u3/xn6chnTXh4HYCJoGYOAbB3WNbAoQR i6u6TLLOvgv9pMNUo6v1qB0xly1faizjimVYBwLhOenkA3Bw7S8UIVfdv 84cO9dFUGcr/Pfrl3GtQ== -----END NEW CERTIFICATE REQUEST-----

   
   
3. The CA (e.g. VeriSign/Thawte) will send you a certificate reply (chain) by email. Copy the chain and store it in a file. Use "keytool -import" to import the chain into your keystore. e.g.

   C:\>C:\jdk1.3\bin\keytool -import -alias MyCert -file 
   		VSSStanleyNew.cer
   

4. Your RSA certificate and its supporting chain have been validated and imported into your keystore. You are now ready to use the jarsigner to sign your JAR file.

Note that you must use the same alias name for all the above steps (or no alias name, in which case the alias name defaults to "mykey").

Netscape Signing Tool

At the time this document was written, most CAs (e.g. VeriSign/Thawte) are known to support Netscape Signing Tool. To use the Netscape Signing Tool to sign applets using RSA certificate, obtain the Netscape Object Signing certificate from Verisign, or Netscape Object Signing certificate from Thawte, or a similar certificate from other CAs. During the process of enrollment, you will be asked about your personal/company information because the CA will need to verify your information before the certificate is issued. This process may take from several hours to several days.

Once the RSA certificate is issued, it usually consists of three files:

• cert7.db
• key3.db
• secmod.db

Depending on the CA, the certificate may be issued and stored in a floppy diskette or be stored directly in the security modules of Netscape Navigator/Communicator. Once it is done, you are ready to use the Netscape Signing Tool to sign your JAR file.

Java Applets

To sign applets with RSA certificates with Jarsigner, the applets must be bundled as JAR files. Jar tool is provided as part of the Java 2 Software Development Kit. For example,

C:>C:\jdk1.3\bin\jar cvf C:\TestApplet.jar .
added manifest
adding: TestApplet.class (in = 94208) (out= 20103)(deflated 78%)
adding: TestHelper.class (in = 16384) (out= 779)(deflated 95%)

This example creates a JAR file C:\TestApplet.jar, and it contains all the files under the current directory and its sub-directories.

After the JAR file is created, you should verify its content using Jar tool again. e.g.

C:>C:\jdk1.3\bin\jar tvf TestApplet.jar 
     0 Mon Mar 06 18:02:54 PST 2000 META-INF/
    68 Mon Mar 06 18:02:54 PST 2000 META-INF/MANIFEST.MF
 94208 Wed Mar 10 11:48:52 PST 2000 TestApplet.class
 16384 Wed Mar 10 11:48:52 PST 2000 TestHelper.class

This ensures that the class files are stored with the proper path within the JAR file.

To sign applets with RSA certificates with Netscape Signing Tool, the applets must be placed in a directory, and the Netscape Signing Tool will bundle it as JAR file after the process of signing.

Signing applets

Once we have the RSA certificates, the signing tool and the applet's JAR files, we are ready to sign the applets.

Signing applets using jarsigner

To sign applets using jarsigner, follow these steps:

1. Use jarsigner to sign the JAR file, using the RSA credentials in your keystore that were generated in the previous steps. Make sure the same alias name is specified. e.g.

   C:\>C:\jdk1.3\bin\jarsigner C:\TestApplet.jar MyCert
   Enter Passphrase for keystore: ********
   

2. Use "jarsigner -verify -verbose -certs" to verify the jar files

   C:>C:\jdk1.3\bin\jarsigner -verify -verbose -certs d:\TestApplet.jar 245 Wed Mar 10 11:48:52 PST 2000 META-INF/manifest.mf 187 Wed Mar 10 11:48:52 PST 2000 META-INF/MYCERT.SF 968 Wed Mar 10 11:48:52 PST 2000 META-INF/MYCERT.RSA smk 943 Wed Mar 10 11:48:52 PST 2000 TestApplet.class smk 163 Wed Mar 10 11:48:52 PST 2000 TestHelper.class X.509, CN=XXXXXXX YYY, OU=Java Software, O=Sun Microsystems, L=Cupertino, ST=CA, C=US (mycert) X.509, CN=Sun Microsystems, OU=Java Plug-in QA, O=Sun Microsystems, L=Cupertino, ST=CA, C=US X.509, EmailAddress=server-certs@thawte.com, CN=Thawte Server CA, OU=Certification Services Division, O=Thawte Consulting cc, L=Cape Town, ST=Western Cape, C=ZA s = signature was verified m = entry is listed in manifest k = at least one certificate was found in keystore i = at least one certificate was found in identity scope jar verified.

   
   
3. Your applet has been signed properly. You are now ready to deploy your RSA signed applet.

Signing applets using Netscape Signing Tool

To sign applets using signtool, follow these steps:

1. Use "signtool -L" to determine the certificate nickname that should be used in signing. e.g.

   C:\signtool13WINNT40\signtool -L -d a:\cert using certificate directory: a:\cert S Certificates - ------------ AT&T Certificate Services Thawte Personal Premium CA GTE CyberTrust Secure Server CA Verisign/RSA Commercial CA AT&T Directory Services BelSign Secure Server CA BelSign Class 1 CA GTIS/PWGSC, Canada Gov. Web CA Thawte Personal Freemail CA Thawte Server CA GTIS/PWGSC, Canada Gov. Secure CA MCI Mall CA VeriSign Class 3 Primary CA VeriSign Class 4 Primary CA KEYWITNESS, Canada CA BelSign Class 2 CA BelSign Object Publishing CA * Sun Microsystems, Inc. VeriSign Class 3 CA - Commercial Content/Software Publisher - VeriSign, Inc. Verisign/RSA Secure Server CA VeriSign Class 1 Primary CA BBN Certificate Services CA Root 1 Thawte Personal Basic CA * Sun Microsystems, Inc.'s VeriSign, Inc. ID CertiSign BR VeriSign Class 2 Primary CA Canada Post Corporation CA Integrion CA IBM World Registry CA BelSign Class 3 CA Uptime Group Plc. Class 1 CA Uptime Group Plc. Class 2 CA Thawte Premium Server CA Uptime Group Plc. Class 3 CA GTE CyberTrust Root CA Uptime Group Plc. Class 4 CA - ------------ Certificates that can be used to sign objects have *'s to their left.

   
   
2. Create an empty directory. e.g.

   mkdir signdir

3. Put all the applet class files into it.
   
4. Use "signtool -Z" to sign the applet. e.g.

   C:\signtool13>signtool -k"Sun Microsystems, Inc.'s VeriSign, Inc. ID" -d a:\cert -Z c:\TestApplet.jar c:\signdir using certificate directory: a:\cert Generating c:\signdir/META-INF/manifest.mf file.. --> TestApplet.class adding c:\signdir/TestApplet.class to c:\TestApplet.jar... (deflated 57%) --> TestHelper.class adding c:\signdir/TestHelper.class to c:\TestApplet.jar... (deflated 43%) Generating zigbert.sf file.. adding c:\signdir/META-INF/manifest.mf to c:\TestApplet.jar... (deflated 44%) adding c:\signdir/META-INF/zigbert.sf to c:\TestApplet.jar... (deflated 46%) adding c:\signdir/META-INF/zigbert.rsa to c:\TestApplet.jar... (deflated 40%) tree "c:\signdir" signed successfully

   
   
5. Use "signtool -w" to verify the archive. e.g.

   C:\signtool13>signtool -w c:\TestApplet.jar -d a:\cert using certificate directory: a:\cert Signer information: nickname: Sun Microsystems, Inc.'s VeriSign, Inc. ID subject name: C=US, ST=CA, L=Palo Alto, OU=Java Software, CN=Sun Microsystems, OU=Digital ID Class 3 - Netscape Object Signing, OU="www.verisign.com/repository/RPA Incorp. by Ref.,LIAB.LTD(c)99", OU=VeriSign Trust Network, O="VeriSign, Inc." issuer name: CN=VeriSign Class 3 CA - Commercial Content/Software Publisher, OU="www.verisign.com/repository/RPA Incorp. by Ref.,LIAB.LTD(c)98", OU=VeriSign Trust Network, O="VeriSign, Inc."

   
   
6. Your applet has been signed properly. You are now ready to deploy your RSA signd applet.

Deploying RSA signed applets

To deploy RSA signed applets:

1. Reference the JAR from the HTML page using ARCHIVE=xyz.jar in the EMBED/OBJECT tag.
2. Put the JAR file and the HTML page on the web server.

When users of Java Plug-in encounter an RSA signed applet, the Plug-in will verify that the applet is correctly signed, and that the RSA certificate chain and the root CA are valid. If these are all valid, the Plug-in will pop up a security dialog that tells the user who signed the applet and provides four options:

1. Grant always: If selected, the applet will be granted "AllPermission". Any signed applet that is signed using the same certificate will be trusted automatically in the future, and no security dialog will pop up again when this certificate is encountered again. This decision can be changed from the Java Plug-in Control Panel.
   
2. Grant this session: If selected, the applet will be granted "AllPermission". Any signed applet that is signed using the same certificate will be trusted automatically within the same browser session.
   
3. Deny: If selected, the applet will be granted the applicable permissions from the security policy of the Java runtime. By default, the permissions granted would be those for untrusted applets.
   
4. More Info: If selected, users can examine the attributes of each certificate in the certificate chain in the JAR file.

Once the user selects an option from the security dialog, the applet will be run in the corresponding security context. Please notice that all these decisions are determined on the fly, and no preconfiguration is required.

Common Problems

• If the JAR file is not signed properly, if the RSA certificate has expired, or if the RSA certificate is a self-generated self-signed certificate, Java Plug-in may fail silently and will not pop up the security dialog. The applet will be treated as unsigned.
  
• The Netscape Signing Tool is very particular about JAR file format. In Netscape Signing Tool, it expects the MANIFEST file to be at the end of the JAR file, whereas Jarsigner puts it at the beginning. The standard does not mandate where the MANIFEST should be in the JAR file. Therefore, if you create a JAR file using Jar tool, the Netscape Signing Tool may complain about "Invalid Jar File Format". On the other hand, Jarsigner is not picky; it can verify JAR files regardless of whether their MANIFEST is at the beginning or at the end. To workaround this problem when using Netscape Signing Tool, you should generate the JAR file and sign it through the tool itself.
  
• Java Plug-in 1.2.2 supports signed applets signed using Netscape Signing Tool 1.2. However, Java Plug-in 1.2.2 fails to authenticate any signed JAR files generated by Netscape Signing Tool 1.3, due to changes in the signature block file of those JAR files. Note that interoperability with Netscape Signing Tool 1.3 has been restored in Java Plug-in 1.3, which also interoperates with Netscape Signing Tool 1.2.