PKI Certificate Types Explained (TLS/SSL, Code Signing, Email, Client)

PKI Certificate Types Explained (TLS/SSL, Code Signing, Email, Client). With growing technological adoption and connectivity, cyber security has become the main concern for modern business leaders. Public Key Infrastructure (PKI) was first privately introduced in the 1970s and was eventually made public in 1995.

Over the years, many refinements and improvements have been to PKI as both a concept and implementation. Today, it provides a foundation for modern cloud security tools and architectures such as Zero-Trust. Nevertheless, there are various ways to implement and use PKI for your business’s cybersecurity. Each area or approach has a certificate associated with it. For instance, PKI certificates exist to help you secure your email messages and document exchanges. The following guide will explain the various PKI certificate types.

Shall we start with PKI Certificate Types Explained (TLS/SSL, Code Signing, Email, Client).

Source: PXHere

What is PKI?

All in all, PKI is a hybrid centralized and decentralized authentication system that facilitates safe and secure asymmetric encryption. It does this by using an independent and impartial certification authority that’s in charge of confirming the identity of people, devices, or applications that possess private keys.

This prevents bad actors from intercepting public keys. Hence, the PKI allows you to ascertain that you’re receiving encrypted files, messages, or data from the correct source. This is done through digital certificates which are also referred to as PKI or X.509 certificates. Each certificate must have a specific set of attributes to be valid. These qualities include:

  • Contains an expiration date.
  • Tamper Proof.
  • Offers information about a specific entity (the sender).
  • Presentable for validation.
  • Contains unique information that allows the certificate to be validated.
  • Issued from a trusted certification authority.
  • Issuer traceable.

PKI Certificate Types

There are different types of PKI certificates. The most prominent types are:

The rest of this guide will be dedicated to explaining these PKI certificate types.

TLS/SSL PKI Certificates

Secure Socket Layer (SSL) and Transport Layer Security (TLS) are the first PKI certificate types you’ll explore in this guide. They are arguably the most used or exchanged PKI certificate types in the world. Many people are unaware of their existence and how they facilitate safe and secure web browsing experiences.

TLS replaced SSL when it was discovered that it had a few vulnerabilities. Today, TLS is used to encrypt and secure private information transmitted over the internet. Websites that use TLS certificates are more trusted than those without.

HTTPS uses TLS to encrypt communication protocol. TLS is used to ensure that user site activity and browsing are kept private. It also secures and encrypts usernames, passwords, and information submitted from forms which may include documents, images, and other files. 

A simple TLS flow is as follows:

Checkout pages for web stores and eCommerce sites are also typically protected using TLS. While your web browser already verifies the validity of website TLS certificates. 

You can also view and ascertain their validity by:

  • Use Google Chrome (since it’s the most popular browser in the world) to navigate to a secure site.
  • Click on the padlock to the left of the address bar.
  • Click on Connection is secure from the context menu.
  • Click on Certificate is valid.

You should be able to view the contents of the TLS certificate. You can view who it’s issued by and to whom, the period of validity, etc. If a website’s certificate is invalid, your web browser will display an error page informing you that the website or resource you’re trying to access is not secured. 

Alternatively, you may see the following message when trying to view the certificate:

Code or Software Signing Certificates

Websites are not the only software components protected by PKI certification. Local programs, applications, drivers, and other software are also protected by digital certificates. These are generally known as code-signing certificates.

They ensure that the software you install on your computer is safe and from a verified source. Furthermore, it ascertains that it has not been tampered with. The Windows operating system uses the Windows Defender antivirus and the User Account Control (UAC) feature to prevent you from installing dubious and uncertified software. Developers can use the Windows App Certification Kit to certify their Windows applications.

Document Signing PKI Certificate

If you’ve worked with PDFs, you may be familiar with certificate-based signatures. Companies and/or individuals must register for unique digital IDs before they can apply a certificate-based signature to a document. These are what is known as document signing (PKI) certificates.

Your digital ID features a public key that is used to encrypt the document when it is signed using a certificate based signature. During the certification process, you’ll be required to specify who may view the document (the recipient group). Then, you also specify the access level of each recipient or recipient group.

For instance, you limit one recipient group to read only while granting another access to edit the document. The latest versions of Adobe Acrobat allow you to use two different methods (certificate authorities) to store your self-signed digital ID and ultimately your certificates. You can use the Public Key Cryptography Standard 12 (PKCS #12) or The Windows Certificate Store (only available on Windows).

Most PDF viewers have features that help you view and manage digital signatures and certificates. However, this function isn’t only limited to PDF documents. For instance, you can use Office 365 to manage and view digital signature and certificate details for Excel, Word, and PowerPoint. Digital Signing certificates are arguably one of the most important certificates for current and future business. They help to protect documents containing important information such as contracts, wills, manuscripts, etc.

Email Signing Certificate

A secure email certificate (S/MIME) secures the communications or connections between two email clients. Your message is encrypted using a public key before it is sent to its destination.

The recipient’s email client then uses a private key to decrypt the message. This ensures that only the specified recipient is allowed to view the email. The recipient client also checks if the digital signature has been tampered with before it opens the email message. If it has been intercepted and somehow altered during transit, the recipient will be notified.

Client or User Identity Certificate

Client certificates involve a mixture of the concepts discussed in the email signing certificate and document signing certificate sections. These PKI certificate types are essentially digital IDs used to identify (client) machines or users.

They ensure that communications or transmissions are sent to the right computers and/or users. These communications may either relate to file transfers (FTP client authentication) or mail messages. The client certificate authenticates both the sender and recipient.

Client and user identity certificates are also be used in multi factor authentication where user credentials and certificate authentication are implemented. This may be ideal for payment gates/online store checkouts, protected servers that only certain clients can access, etc.

Verified Mark Certificate (VMC)

Source: PXHere

Most PKI certificate types are esoteric – at least to the common user. You never really see the mechanisms that govern them in action. Verified Mark Certificates (VMCs) are different. They are primarily used for email messages and brand authentication.

With phishing being one of the most prevalent types of cyberattacks, email messaging requires a multi-pronged approach for authentication and protection. VMCs are specifically designed to be used for email marketing or business to client correspondence. However, it will soon be used in more applications. It’s still a relatively new technology.

A VMC ensures that your company and its brand comply with Domain-based Message Authentication, Reporting, and Conformance (DMARC) email standards. Furthermore, it ensures that all your messages are valid and sent from your domain.

VMC allows you to display your logo instead of your initials/name in the email client. Not only can this be used to prove the validity of your messages but it allows you to further your branding too.

The VMC is issued by an official certificate authority that verifies the brand logo ownership. This protects your logo from being used by bad agents for nefarious purposes such as spamming and phishing. Logos must be registered trademarks before they are certified with VMC. These logos are more difficult to falsify and/or spoof.

Thank you for reading PKI Certificate Types Explained (TLS/SSL, Code Signing, Email, Client). We will conclude this article now. 

PKI Certificate Types Explained (TLS/SSL, Code Signing, Email, Client) Conclusion

Different PKI Certificate Types Explained (TLS/SSL, Code Signing, Document, Client, Verified Mark, Email) . The latest versions of Windows feature a built-in Code Signing utility called SignTool. It’s a CLI tool that allows you to digitally sign files and verify the digital signatures of files. If you’re interested in seeing how PKI certificates work from a practical standpoint, you can start here.

Nevertheless, the above guide discusses the most prominent PKI certificate types and how they can be employed, managed, and used. Hopefully, this guide helps you improve your company’s cybersecurity posture. If you have any questions or corrections, please leave a comment down below. As always, thank you for reading.    

If you fancy reading more content about PKI, please navigate to our blog over here

Avatar for Mduduzi Sibisi
Mduduzi Sibisi

Mdu is an Oracle-certified software developer and IT specialist, primarily focused on Object-Oriented programming for Microsoft and Linux-based operating systems. He has over a decade of experience and endeavors to share what he's learned from his time in the industry. He moonlights as a tech writer and has produced content for a plethora of established websites and publications - including this one. He's always open to learning and growing.

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