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What is an X.509 Certificate and How Does It Work?


Data security, user privacy, and information integrity are vital properties of today’s internet protocols and applications. The application of the internet in commercial activities such as online shopping, banking transactions, and eCommerce has significantly increased the value of critical data. Consequentially, networking protocols and applications have been developed for the purposes of safeguarding essential data through encryption, entity authenticity, and, most importantly, data integrity.

However, application developers and protocol designers have always found it difficult to attain these objectives, so they rely on more established security protocols such as TLS and SSL protocol suites. The reason is that these protocols are built on thoroughgoing and excellently-analyzed cryptographic algorithms. Public key infrastructure (PKI) made with the X.509 standard is responsible for authentication.

This article provides fine details about X.509 certificates and discusses why they are more condescending than conventional authentication.

The X.509 Digital Certificate, What is it?

The International Telecommunications Union (ITU) standards define the format of public key infrastructure certificates. The X.509 certificate is one of the digital certificates based on ITU standards. The certificate employs the PKI infrastructure to verify that a particular public key belongs to a given computer, service, or user. The certificate was first introduced in 1988 alongside the X.500 standards that are widely applicable in electronic delivery services. Since then, the certificate has been widely adapted for use on web-based protocols.

So, in one sentence, what is an X.509 certificate? An X.509 certificate refers to a special kind of digital certificate that employs international X.509 standards to verify the ownership of public keys.

How the X.509 Certificate Works

The X.509 certificate is a popular format for digital certificates. It is based on asymmetric cryptography. This type of cryptography applies a pair of distinct yet mathematically-related keys- the public key and the private key. Sensitive data will be encrypted using the public key. Its corresponding private key will be used to decrypt encrypted data.

The public key is open for public use (hence its name). Anyone can access it and use it to encrypt information. However, upon encryption, the data can only be decrypted by using the corresponding private key. As you can imagine, the private key must be concealed at all costs to protect it from landing in unsafe hands. Only the authorized machines and servers will be able to access the private key.

Cryptographic mechanisms can be easily analyzed depending on the security level they offer. It is also easy to check the correctness of the implemented algorithms. However, the X.509 certificate infrastructure relies not only on cryptography but also on entities or authorities, and these organizations are referred to as certificate authorities.

Certificate authorities will help in the certificate of public keys and identities of other certificates in the X.509 certificate.

Elements of the X.509 Certificate

Each X.509 certificate is characterized by several attributes and features that give some details about the certificate owner, the issuer, and the associated cryptographic parameters.

To review the attributes and fields of a typical X.509 certificate, we will inspect the composition of an SSL certificate as shown in the Google Chrome browser. You can check this by clicking on the padlock icon on the left side of any HTTPS website.

In addition to the signature, all X.509 certificates have the following attributes;

  • Version – This identifies the version of the X.509 standard that is applicable to the certificate. The version can directly impact the information specified in the certificate. Thus far, there are only three versions. The X.509 version 1 was the most original version available since 1988. It is considered to be the most generic version. Later came the X.509 version 2, which introduced the concept of subject and identifier that would address the possibility of reuse of subject and issuer names. The X.509 version 3 is the most recent version, released in 1996. It is majorly known for its extension notion, whereby anyone can define an extension and include it in the certificate.
  • Serial Number – The certificate authority that issued the certificate must give a unique serial number to every certificate to distinguish it from other certificates. The serial number is essential in many ways. For instance, whenever the certificate is revoked, it is the serial number that is placed on the certificate revocation list.
  • Signature Algorithm Identifier – This identifies the cryptographic algorithm used by the certificate authority to sign the certificate.
  • Issuer – This indicates the name of the certificate authority that signed the certificate. Using the certificate implies that you trust its issuer (the certificate authority). The issuer can sign its own certificates in a few cases, such as the root or top-level certificates.
  • Validity Period – Digital certificates are usually valid for a specific period. The validity period describes the start date and time and the end date and time with which the X.509 certificate will remain valid. As long as the certificates remain valid, entities can rely on them, as long as the associated private key is not compromised.
  • Subject Name – This is the field that describes the name of the entity to which the certificate is issued. The name must adhere to the X.500 standards, which is why it should be unique across the web.
  • Subject Public Key Information This field identifies the public key associated with the identity and the algorithm identifier specifying the public key cryptography system the key belongs to as well as the associated key parameters. Here is a pictorial representation of the X.509 certificate pulled from the Amazon site.

Applications of X.509 Certificates

The following are some of the popular applications for the X.509 certificate;

SSL/TLS And HTTPS Encrypted Safe Browsing

This is the most common use of this certificate. Public key infrastructure has been known to be the basis of all SSL and TLS protocols, which are fundamentally the HTTPS secured browser connections.

Without an SSL certificate, cyber attackers will find easy loopholes in users’ sensitive data and IP addresses and exploit them using a series of attacks such as Man-in-the-middle attacks. But with SSL certificates, all communications between two communicating ends over the internet will remain encrypted and safe from hackers.

Code Signing Certificates

Code Signing Certificates are significant in application and software scripts because they allow developers to digitally sign them and add a security layer. The end users can be sure that the software of the application has not been tampered with in any way since it was signed.

To help verify the code, the digital certificates will include the developer’s signature, the company’s name, and the timestamp.

Encrypted Email Standards Such As S/MIME And PEM

S/MIME certificates are vital because they help in the validation of email senders and in the encryption of email contents. By encrypting and decrypting email communications, as well as identity validation, S/MIME certificates provide assurance to the users regarding the validity and authenticity of emails.

Thus, they help safeguard email communications against increasingly sophisticated social engineering attacks such as phishing and spear-phishing.

SSH Keys

Being a part of the x.509 certificates, SSH keys offers secure access to credentials in the SSH protocol. Here, the SSH protocol is used in cloud computing, file transfer, and tools related to configuration management. Most entities will require the SSH keys to help in the authentication of identity and protection of associated services from threats such as malicious attacks.

Apart from enhancing application security, SSH keys are vital in automating connected services, single sign-on, and identity management.

Digital Identity Automation

X.509 certificates are also known to offer effectual authentication of digital identities. As the information held in digital resources continues to expand beyond conventional networks, mobile devices, cloud storage systems, and IoT, the need to secure identities becomes more important. Note that digital identities are not only restricted to conventional devices. They can also be applied in the authentication of users, data, or web applications.

The X.509 applies this standard by replacing passwords that are more prone to dictionary and brute-force attacks.

FAQs About X.509 Certificates

Here are some of the most frequently asked questions about these certificates;

How Do I Get The X.509 Certificate?

You can purchase digital certificates from trusted certificate authorities or resellers. Create the CSR and submit it to the SSL provider, complete the configuration process and validate yourself via email, file-based verification method, submit the business-related documents if required, and finally get your SSL certificate.

Is There Any Difference Between SSL Certificate and X.509 Certificate?

SSL is the most prevalent use of X.509 certificate. However, although most people use the terms interchangeably, you should note that the two terms do not refer to the same thing. SSL/TLS certificate is an X.509 certificate characterized by extended key usage.

How are X.509 Certificates Validated?

The certificate verification process requires each certificate to be signed by the same issuer certificate authority named in its certificate. The client should be able to follow a hierarchical path that repeatedly links back to the root certificate authority listed in the client’s trust store.


X.509 certificates is a common term you will hear along the corridors of internet application and web security. However, you might not know what it is, or you might not be ready to bet your money on its definition and how it works.

This article has explained what an X.509 certificate is, how it works, and its attributes, and also answered some of the frequently asked questions about this certificate.

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