Microsoft Authenticode Code Signing in Linux with Jsign

Jsign is an open-source, platform-independent Java tool for Microsoft Authenticode code signing. Jsign is easy to integrate with build systems like Maven, Gradle, and Ant, or can be used directly from the command line.

In this how-to we’ll cover using Jsign from the Linux command line for OV/IV code signing and EV code signing. Because Jsign is Java based, you can also use it on Windows and MacOS systems.

Install Jsign

First, you’ll have to download and install Jsign. The Jsign website includes links to Debian and RPM packages for easy installation on most popular Linux systems, as well as a .jar file.

OV/IV Code Signing

For standard OV/IV code signing you can use a certificate stored in a Java keystore or PKCS#12 (PFX) file. SSL.com delivers code signing certificates in PKCS#12 format, so we’ll use that for our example. In all code examples below, replace the values shown in ALL-CAPS with your actual values.

1. First, use the keytool command to get the alias value to use when signing:

   keytool -list -v -keystore PKCS12-FILE.p12 -storetype PKCS12 -storepass PKCS12-PASSWORD

2. Check the output of your keytool command for a line beginning with Alias name:.

   Keystore type: PKCS12
   Keystore provider: SUN
   
   Your keystore contains 1 entry
   
   Alias name: 1
   Creation date: Jan 18, 2021
   Entry type: PrivateKeyEntry
   Certificate chain length: 4
   
   ...

   In the above example, Alias name is 1.

3. Use a command like the following to sign and timestamp a file:
   • jsign command installed system-wide:

     jsign --keystore KEYSTORE.p12 --alias ALIAS-NAME --storetype PKCS12 --storepass PKCS12-PASSWORD --tsaurl http://ts.ssl.com --tsmode RFC3161 FILE-TO-SIGN

   • With Jsigner .jar file:

     java -jar jsign-3.1.jar --keystore KEYSTORE.p12 --alias ALIAS-NAME --storetype PKCS12 --storepass PKCS12-PASSWORD --tsaurl http://ts.ssl.com --tsmode RFC3161 FILE-TO-SIGN

4. If your command is successful, you should see output like the following:

   Adding Authenticode signature to example.exe

EV Code Signing

You can also use Jsign with an EV code signing certificate. The example here uses an SSL.com EV code signing certificate installed on a YubiKey FIPS token.

1. First, make sure that OpenSC is installed on your system so it can communicate with your token via the PKCS#11 API. On Debian-based distros like Ubuntu you can install OpenSC with apt:

   sudo apt install opensc

2. Next, create a configuration file. The name of the file is arbitrary, but for the example commands below we’ll use eToken.cfg. Note that the path to opensc-pkcs11.so may vary in your OpenSC installation, so check before creating the config file.

   name = OpenSC-PKCS11
   description = SunPKCS11 via OpenSC
   library = /usr/lib/x86_64-linux-gnu/opensc-pkcs11.so
   slotListIndex = 0

3. Use the keytool command to get the alias value to use when signing:

   keytool -list -v -keystore NONE -storetype PKCS11 -storepass TOKEN-PIN -providerClass sun.security.pkcs11.SunPKCS11 -providerArg eToken.cfg

4. Check the output of your keytool command for a line beginning with Alias name:. If your token contains multiple certificates, check the validity dates and issuer in the output against your certificate. Note that EV code signing certificates issued on YubiKey from SSL.com should have an alias name of Certificate for PIV Authentication.

   Alias name: Certificate for PIV Authentication
   Entry type: PrivateKeyEntry
   Certificate chain length: 1
   Certificate[1]:
   Owner: OID.1.3.6.1.4.1.311.60.2.1.3=US, OID.1.3.6.1.4.1.311.60.2.1.2=Nevada, OID.2.5.4.15=Private Organization, CN=SSL Corp, SERIALNUMBER=NV20081614243, O=SSL Corp, L=Houston, ST=TX, C=US
   Issuer: CN=SSL.com EV Code Signing Intermediate CA RSA R2, O=SSL Corp, L=Houston, ST=Texas, C=US
   Serial number: 7299f93a57bac3c6570f781580e63172
   Valid from: Fri Apr 17 12:46:04 EDT 2020 until: Sat Apr 17 12:46:04 EDT 2021

5. Use a command like the following to sign and timestamp a file:
   • jsign command installed system-wide:

     jsign --keystore eToken.cfg --alias "Certificate for PIV Authentication" --storetype PKCS11 --storepass TOKEN-PIN --tsaurl http://ts.ssl.com --tsmode RFC3161 FILE-TO-SIGN

   • With Jsigner .jar file:

     java -jar jsign-3.1.jar --keystore eToken.cfg --alias "Certificate for PIV Authentication" --storetype PKCS11 --storepass TOKEN-PIN --tsaurl http://ts.ssl.com --tsmode RFC3161 FILE-TO-SIGN

6. If your command is successful, you should see output like the following:

   Adding Authenticode signature to example.exe

Verify Digital Signature

1. You can verify that your digital signature is valid by viewing the signature details in Windows.
   
2. You can also use SignTool in Windows to verify the digital signature.

   signtool.exe verify /pa 'C:\Users\Aaron Russell\Desktop\example.exe'
   File: C:\Users\Aaron Russell\Desktop\example.exe
   Index  Algorithm  Timestamp
   ========================================
   0      sha256     RFC3161
   
   Successfully verified: C:\Users\Aaron Russell\Desktop\example.exe