What Is an X.509 Certificate & How Does It Work?

In June 2021, CD Projekt Red, the developers of games like Cyberpunk 2077, suffered a ransomware attack on their database. However, the developer refused to negotiate, and sensitive data was published on the public platform. Such malicious attacks can influence your business, so having an X.509 Certificate for your website becomes essential.

An X.509 certificate is a digital certificate accepted by the International Telecommum Union(ITU) X.509 Standard. It defines the public key infrastructure certificate format. The structural strength of this certificate is a pair of public and private keys. These security keys help encrypt and decrypt data.

Organizations can use X.509 certificates to encrypt data and enforce HTTPS protocol to enable secure browsing. Understanding this certificate, why you need it, and how it works are some crucial questions we will answer through this article.

What is an x509 certificate?

X.509 certificates are vital to ensuring application and website security. It is a digital certificate that helps secure communication between a browser and a user’s device. You can use it for,

  • Encrypted web browsing,
  • Email encryptions using the S/MIME protocol,
  • Code signing certificate of applications,
  • Document signing,
  • Client authentication.

Digital certificates allow individuals, companies, and devices to ensure higher security for data exchange. This is especially important when your organization stores, processes, and shares massive user data.

For example, if you are a financial app or e-commerce business, you must comply with the Payment Card Industry Data Security Standard (PCI DSS). An X.509 certificate helps secure users’ sensitive information and comply with security standards. Not just security standards and regulatory compliance, such digital certificates are crucial to maintaining user trust.

Now that you know what X.509 certificate is, let us understand how it works!

How Do X.509 Certificate Work?

X.509 certificates are based on Abstract Syntax Notation One (ASN.1), which is a standardized notation. ASN.1 describes the data structure exchanged through messages between two systems.

X.509 uses ASN to encrypt and decrypt data transmitted from one system to other. It uses a public key infrastructure (PKI) system for encryption. PKI is a set of roles, policies, software, and hardware required to manage digital certificates.

X.509 certificates use PKI to establish public key encryptions, ensure the security of messages sent from systems, and verify the sender’s authenticity.

However, how does X.509 manage to verify the sender’s authenticity?

Think of a locker in the bank that has two keys. Without these keys, you can never open the locker. A message is a locker closed by a public key, and only receivers with private keys can open it.

However, there is one key difference between the locker in your bank and encrypted data.

The public key used to encrypt the data is -published by software publishers for users. Therefore, you need advanced cryptographic encryption to avoid any cyberattacks.

So, most public keys are encrypted through a complex cryptographic algorithm. Similarly, a private key with a random string of alphanumeric values is generated to match the public key and decrypt data.

One of the most common algorithms used for encryptions is,

  • Advanced Encryption Standard (AES) is a symmetric block of cipher established as a FIPS-approved cryptographic algorithm. It uses 128-bit blocks with keys sized 128,192 and 256 bits for encryption. The decryption process using the AES algorithm is similar to the encryption process.
  • Rivest-Shamir-Adleman (RSA) is an algorithm based on asymmetric encryption. It has two security keys, one for encryption and the other for decryption. RSA is a standard encryption algorithm used for internet-facing applications and websites.
  • Triple DES is upgraded version from the classic Data Encryption Standard (DES) algorithm. It uses symmetric encryption where both security keys used for encryption and decryption are the same.

Here are the steps involved in X.509 certificate signing,

  • An unsigned certificate with a public key is first hashed using a hashing algorithm
  • The hashed file is sent to a certificate authority(CA) for encryption through a certificate signing request(CSR)
  • The hashed file is encrypted by certificate authority after submission CSR using its private key
  • The encrypted file helps protect data and verify the identity of a publisher using CA’s public key

Now that you know how it works, here is why you need to consider buying and installing one for your applications

Reason to use the X.509 certificate

There are multiple reasons for choosing an X.509 certificate as a business. From broader use cases to increased level of trust, such digital certificates help ensure higher security for applications.

Broader use case

You can use X.509 certificates for multiple use cases, including browser security, secure server communications, online document signing, SSH keys, and data protection. One of the most critical aspects of using such a digital certificate is how it allows businesses to improve brand reputation with enhanced security.

Publisher validations

Software publishers introduce new products in the market, and users download them. However, due to cybersecurity issues, software source code can be tampered with. This is where X.509 certificates ensure that the source code is intact and software is secure for users to install on their devices. Browsers have a list of valid certificates that match yours before they allow users to download it.

If your certificate is not on the browser’s list, it will show a warning sign leading to a lack of trust among users for your software or website.

Data protection and compliance

One of the key reasons to use X.509 certificates for your websites is data protection. There are several data regulations and standards that you need to comply with, and this digital certificate helps you improve compliance.

For example, European Union (EU) has a specific set of standards called the General Data Protection Regulation (GDPR). So if your business is operational in the EU, GDPR compliance becomes vital. X.509 certificates help you ensure compliance across data regulation standards.

Now that we know why you need an X.509 certificate. Let us understand its components and structural elements.

Components of the X.509 certificates

X.509 certificates have several key components that help secure the information for your applications.

Information fields

An X.509 certificate has the following information fields,

  • Version– What version of X.509 certificate is it?
  • Serial number– A unique serial number that the CA issues to differentiate the certificate from others.
  • Algorithm– Which algorithm does the certificate used?
  • Issuer’s name– What is the name of the CA?
  • Certificate validity– For how much time will the certificate be valid.
  • Name of the subject– name of the SSL requestor
  • Public key information of the requestor– Which public key is associated with the requestor?

Apart from the information field, there are multiple extensions you can use to secure information.

X.509 certificate extensions

Two common X.509 certificate extensions you can use for signing your websites and apps are

  • Subject Alternative Name (SAN) Extension– It allows businesses to use certificates for signing multiple domains. Such domains can include DNS names; email IDs, and subdomains. Many CAs use SAN-based multiple-domain certificates for businesses.
  • Key Usage– It is an extension that restricts the use of security keys for specific purposes only. For example, you can limit the usage of security key for signing only and not for decryption.

Certificate Revocation Lists (CRLs)

Every browser has a revocation list with all the valid digital certificates listed. It is essential for browser security, and you must ensure that your certificate is in the CRL. If not, it can cause a lack of trust among users, as they will see a warning sign from the browser.

Now that we know the X.509 certificate’s components. How they work, let us understand its uses.

Uses of X.509 certificate

Cybersecurity requires enforcement of different protocols, and the X.509 certificate helps enforce them.

Server security

When a user requests data from the browser, it fetches the data from the server. The communication between the user’s device, browser, and web server needs to be secure. X.509 certificates enforce HTTPS protocol to secure communication between the user’s device and browser.

Digital signatures

PKI base of the X.509 certificates helps application developers and software publishers to code sign their apps. They can digitally sign applications and ensure that the source code remains intact.

Document signing

E-signature software firms and digital document repository services can leverage X.509 certificates to sign documents. It ensures that sensitive information in the digital document is secure through a Code Signing certificate.

Email security

You can use X.509 certificates to enforce S/MIME protocol and secure email messages. It helps encrypt the email contents and protects the data against social engineering practices used for cyber-attacks.

SSH Protocols

X.509 certificate help in Secure Shell (SSH) key generation for apps that provides secure data access. Further, it enables businesses to implement SSH protocol to secure communications, cloud services, network environments, and configuration management tools.

How Do I Get an X.509 Certificate?

You can get an X.509 certificate from CAs that offer digital certificate services. The first step is to submit a CSR with all your details. What kind of details you need to provide depends on the type of certificate.

For example, Domain Validation (DV) certificates require information about the ownership of a domain. Once you submit the CSR, CAs validate the identity of the requestor and, after validation, issue the certificate. If you choose business validation or extended validation then, the certificate authority will check additional business related documents and it will take 4-5 days in issuance of a certificate.

How does the chain of trust form?

Every X.509 certificate has a chain of trust or a hierarchy of CAs. There is a root certificate where the CA information is stored. Further, the hierarchy has intermediate certificates with the chain of trust leading to end-user certificates.

Therefore, whenever a user tries to access your website, the browser will validate the publisher’s identity along the chain of trust. It is essential to understand that there can be many intermediate certificates between the end user certificate and the root certificate in the chain of trust.

Recommended Reading: Root Certificates vs Intermediate Certificates

How does revocation work for X.509?

Certificate revocation is a process to invalidate X.509 certificates about expiring. Revoking the certificate is key to ensuring that your users are not exposed to cyberattacks. If your certificate is expired, it can lead to cyberattacks.

Therefore, you need to revoke a certificate before it expires and renew it to ensure continuous protection. CRL has all the certificate information stored along with revocation details. Browsers download and refer to CRL to ensure that the certificate installed on the website is valid.

Another way to check for certificate revocation is Online Certificate Status Protocol (OCSP), where the browser sends a validation request directly to CA. Therefore, as a website owner or software publisher, it is crucial to revoke the certificate before expiration.

Conclusion for X.509 Certificate

Cybersecurity challenges are increasing, and businesses must stay updated with application security. Using X.509 certificates, you can ensure application security and that users’ credentials are not exposed to cyberattacks.

You need to understand the structure of such certificates. How they work, and how to use them for your business. We have discussed the components of such certificates and the use cases, but how to use them for your business will depend on specific needs.


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