Sign Executables with Code Sign Certificate

5 Min. Read

Featured Photo by Nate Grant from Unsplash

It is standard practice to download programs from the web. However, with the increasing numbers of software programs, there have been increased concerns of malware transferring through the downloadable software. That means that software developers must find a way to ensure that they protect their software from getting infected with malware and distributed to people across the web.

In this article, we will show you how to sign executables with a code sign certificate.

How does code signing work?

The code signing certificate is where developers and software publishers attach a unique digital signature to plugins, applets, and executable files before publishing and distributing them. Most operating systems, software applications, and mobile networks require a trusted digital signature to confirm the integrity of a code and authenticate its source.

How code signing certificate work?
Image Source – ClickSSL.net

What are digital signatures?

A digital signature is an authentication technique that allows a software developer to embed a code in their program to confirm their authenticity. There are several forms of signing algorithms like the Digital Signature Algorithm (DSA) from the National Institute of Standards and Technology (NIST).

When software developer signs their software, they prove to browsers and operating systems that the source of the code can be trusted. That shows that there has not been any proliferation of the software, and therefore the program is safe to use.

Sign executables

How do you sign an executable file? Signing a software program is not a complicated process. However, if you have an executable file you want to sign, here is how:

  • First, you need to download the Microsoft SignTool which is a command-line tool that digitally signs files, verifies the signatures in files, and timestamps files. SignTool is available as part of the Windows SDK.
  • On your Windows machine, start by opening the Start menu.
  • Click the Windows button in the navigation bar of the computer.
  • Type Cmd and choose the command prompt.

After the prompt opens, you can then run a command. The command you choose to use depends on whether you are working with a regular personal information exchange (PFX) file or a password-protected file.

Here is an example of how to sign an executable with a certificate PFX file:

Signtool.exe sign /tr http://timestamp.digicert.com /td sha256 /fd sha256 /f "C:\path\to\yourcert.pfx" /p pfxpassword "C:\path\to\execfile.exe

Can you timestamp an executable while signing it?

With a code signing timestamp, one can verify if the software was valid when downloaded. Also, it allows the user to access the software even though the certificate has expired. That said, after expiry, a user may struggle with updates.

The timestamp will also give a verifiable way of knowing the moment when a developer signed their software. If any alteration happens to the software, the users can recognize that the file is untrustworthy. It is possible to timestamp during the signing process. Although an option part, it is essential. That is because it makes it possible to know if a digital signature is valid long after the signing certificate expires. Some protocols to use for timestamping are RFC 3161 and Microsoft Authenticode.

What does signing in computer science entail?

This signing in computer science involves implementing a mathematical technique to confirm the integrity and authenticity of software, message, or document.

Code signing starts with public-key encryption. Encryption involves encoding a message to protect it from unauthorized access. You generally use a mathematical function to alter values in the original program. To decode the original program, one needs a key to get the values back to their original state, making them readable. For public-key encryption, the key that encodes and the one that decodes are different (Asymmetrical). The reason for referring to it as a public key is that one key is public while the other remains private to ensure the security of the message. With this kind of encryption, the private keys need to be safe and unavailable to unauthorized and malicious persons.

Another way to encode without using the key pairs is to use cryptography. Hash functions are one such method to provide encryption that one can not alter. Hash functions are best when you have a set value and do not need to reread the information.

Understanding code signing certificates

For a software developer to sign their work, they need to have a public/private key pair. To generate it, they can use locally available software tools.

The developer will then issue the public key to a trusted CA to verify the identity information and issue a certificate. This code signing certificate will have the CA’s private key and the public key and identity of the developer’s organization.

The public key will be present in the trust stores of most operating systems and browsers. When a user downloads a software program, they will use the public key to confirm the authenticity of the signing certificate in the software and ascertain if it comes from a trusted CA. The public key will decrypt the encrypted hash to verify that the software was safe from alteration and tampering during transmission.

Code signing certificates ensure that the software is not tampered with or compromised. They signify a high level of trustworthiness by ensuring that digital content remains as safe as it was when it came from the publisher.

These certificates are indispensable attributes for any software developer since they preserve intellectual property and reputation. You can find a cost-effective cheap code signing certificate to protect your digital goods.

Can you tell if a code is signed?

Yes, it is possible to know if a code is signed. Here is how to verify and view certificates:

  • Right-click on the executable file, select “Properties” and then click the “Digital Signatures” tab.
  • Then hit the “Details” button.
  • On the “Digital Signature Details” window, click “View Certificates“.
Digital Signature Details
Digital Signature Details

You should see the code signing certificate at the “Your Certificates” tab of the Certificate Manager window.

How do you tell if an Assembly is signed?

To test and verify your signature, you have two options:

Option 1)

  • Right-click on the assembly file.
  • Then head to the context menu and select “Properties“.
  • In the properties window, you should see a Digital signatures tab. The signature will be displayed in the Signature list section.

Option 2)

You could also use the SignTool to verify if the assembly is signed:

  • Go to: Start > Run
  • Type CMD > click OK
  • At the command prompt, enter the directory where the SignTool exists. By default, the tool is installed in the \Bin folder of the Microsoft Windows Software Development Kit (SDK) installation path (Example: C:\Program Files (x86)\Windows Kits\10\bin\10.0.22000.0\x64\signtool.exe).
  • Last, run the following command:
Signtool.exe verify /pa /v "C:\filename.exe"

Pros of code signing certificates

With a certificate, you can certify content integrity. It means that digital goods are safe from hacking, counterfeiting, and redistribution. A code signing certificate gives source authentication. Users know that the code is legitimately from the developer because they can identify the software author. Code signing certificates engender greater customer confidence. Users are sure that they are using trustworthy software. Most browsers will not allow action commands from unverified sources. Therefore, a code signing certificate will allow for seamless browser integration.

Conclusion

Digital signatures are the perfect assurance of integrity and trustworthiness. It gives the end-users confidence that their software and drivers are legitimate without third-party alterations and compromise. Any software developer that intends on distributing digital goods over the internet should therefore ensure security using a code signing certificate. Failure to which one risks corruption, modification, and impersonation of their digital goods.

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Thank you for reading my blog.

If you have any questions or feedback, please leave a comment.

-Charbel Nemnom-

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