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In Security Last updated: January 31, 2023
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When devices are communicating with each other over the internet, a key challenge they face is ensuring information being shared is coming from a legitimate source.

For instance, in the case of a man-in-the-middle cyber attack, a malicious third party intercepts communications between two parties eavesdropping on their communication and controlling the flow of information between them.

In such an attack, the two communicating parties may think they are communicating directly with each. In contrast, there is a third intermediary who relays their messages and directs their interaction.


X.509 Certificates were introduced to solve this problem by authenticating devices and users over the internet and providing secure communication.

An X.509 certificate is a digital certificate used to verify the identity of users, devices, or domains communicating over a network.

A digital certificate is an electronic file used to identify entities communicating over the networks such as the Internet.

X.509 certificates contain a public key, information on the certificate’s user, and a digital signature used to verify that it belongs to the entity with it. In the case of X.509 certificates, digital signatures are electronic signatures that are created using the private key contained in the X.509 certificates.

X.509 certificates are made according to the International Telecommunications Union(ITU) standard, which provides guidelines on the format of Public Key Infrastructure(PKI)  to ensure maximum security.

X.509 certificates are very useful in securing communication and preventing malicious actors from hijacking communication and impersonating other users.

Components of an X.509 Certificate


According to RFC 5280, a publication by the Internet Engineering Task Force(IETF), which is responsible for coming up with standards that comprise the internet protocol suite, the structure of an  X.509 v3 certificate is made up of the following components:

  • Version – this field describes the version of the X.509 certificate being used
  • Serial Number – a positive integer assigned by the certified authority(CA) to each certificate
  • Signature – contains an identifier for the algorithm that was used by the CA to sign the particular X.509 certificate
  • Issuer – identifies the certified authority that signed and issued the X.509 certificate
  • Validity – identifies the time period when the certificate will be valid
  • Subject – identifies the entity that is associated with the public key that is stored in the certificate’s public key field
  • Subject Public Key Info – contains the public key and the identity of the algorithm with which the key is used. 
  • Unique Identifiers – these are unique identifiers for subjects and issuers in case their subject names or issuer names are re-used over time.
  • Extensions – This field provides methods for associating additional attributes with users or public keys and also managing relationships between certified authorities.

The above components constitute the X.509 v3 certificate.

Reasons to use an X.509 Certificate


There are several reasons to use X.509 certificates. Some of these reasons are: 

#1. Authentication

X.509 certificates are associated with specific devices and users and cannot be transferred between users or devices. This, therefore, provides an accurate and reliable way of verifying the true identity of entities accessing and utilizing resources in networks. This way, you keep off malicious impersonators and entities and build trust between each other.

#2. Scalability

the public key infrastructure that manages X.509 certificates is highly scalable and can secure billions of transactions without getting overwhelmed.

#3. Ease of Use

X.509 certificates are easy to use and manage. Additionally, they eliminate the need for users to create, remember and use passwords to access resources. This reduces the involvement of users in verification, making the process stress free for users. Certificates are also supported by many existing network infrastructures.

#4. Security

The combination of features provided by X.509 certificates, in addition to its performing encryption of data, secure communication between different entities.

This prevents cyber attacks such as man-in-the-middle attacks, the spread of malware, and using compromised user credentials. The fact that X.509 certificates are standardized and regularly improved makes them even more secure.

Users stand to benefit a lot by using X.509 certificates to secure communications and verify the authenticity of the devices and users they are communicating with.

How X.509 Certificates work


A key thing about X.509 certificates is the ability to authenticate the identity of the certificate holder.

As a result, X.509 certificates are typically gotten from Certificate Authority(CA) which verifies the identity of the entity requesting the certificate and issues a digital certificate with a public key associated with the entity and other information that can be used to identify the entity. An  X.509 certificate then binds an entity to its associated public key.

For instance, when accessing a website, a web browser requests the web page from a server. The server, however, does not serve the web page directly. It first shares its X.509 certificate with the client web browser.

Once received, the web browser verifies the authenticity and validity of the certificate and confirms that it was issued by a trusted CA. If that’s the case, the browser uses the public key in X.509 certificate to encrypt data and establish a secure connection with the server.

The server then decrypts the encrypted information sent from the browser using its private key and sends back the information requested by the browsers.

This information is encrypted before being, and the browser decrypts it using the shared symmetric key before displaying it to the users. All the information needed to encrypt and decrypt this information exchange is contained in the X.509 certificate.

Uses of X.509 certificate


X.509 certificate is used in the following areas:

#1. Email Certificates

Email certificates are a type of X.509 certificates that are used to authenticate and secure email transmission. Email certificates come as digital files, which are then installed on email applications.

These email certificates, which use the public key infrastructure(PKI) allow users to digitally sign their email and also encrypt the contents of the emails being sent over the internet.

When sending an email, the sender’s email client uses the receiver’s public key to encrypt the content of the email. This is, in turn, decrypted by the receiver using their own private key.

This is beneficial in preventing a man-in-the-middle attack as the contents of emails are encrypted in transit and thus cannot be deciphered by unauthorized personnel.

To add digital signatures, email clients use the sender’s private keys to sign outgoing emails digitally. The receiver, on the other hand, uses the public key to verify that the email came from the authorized sender. This also helps prevent man-in-the-middle attacks.

#2. Code Signing

For developers and companies that produce code, applications, scripts, and programs, the X.509 certificate is used to put a digital signature on their products, which can be code or a compiled application.

Based on the X.509 certificate, this digital signature verifies that the code shared is from the authorized entity and that no modifications have been made to the code or application by unauthorized entities.

This is particularly useful in preventing the alteration of code and applications from including malware and other malicious code that can be exploited to cause harm to users.

Code signing prevents tampering with application code, especially when it is shared and downloaded on third-party download sites. Code signing certificates can be gotten from a trusted certificate authority such as SSL.

#3. Document Signing


When sharing documents online, it is very easy for documents to be altered without detection, even by people with very little technical skills. All that is needed is the right document editor and photo manipulation application to do the job.

Therefore, it is particularly important to have a way of verifying that documents have not been altered, especially if they contain sensitive information. Unfortunately, traditional hand-written signatures can’t do this.

This is where document signing using X.509 certificates comes in handy. Digital signing certificates that use X.509 certificates allow users to add digital signatures to different document file formats. To do this, a document is signed digitally using a private key and then distributed along with its public key and digital certificate.

This provides a way of ensuring that documents shared online are not tampered with and protecting sensitive information. It also provides a way to verify the true sender of documents.

#4. Government-issued electronic ID


Another application of the X.509 Certificate is to provide security to validate the identity of people online. To do this, X.509 certificates are used together with government-issued electronic ID for the purpose of verifying the true identity of people online.

When someone gets a government-issued electronic ID, the government agency issuing the electronic ID will verify the individual’s identity using traditional methods such as passports or a driver’s license.

Once their identity has been verified, an X.509 certificate associated with an individual electronic ID is also issued. This certificate contains the individual’s public key and personal information.

People can then use their government-issued electronic ID together with their associated X.509 certificate to authenticate themselves online, particularly when accessing government services over the internet.

How to get an X.509 certificate


There are several ways of obtaining an x.509 certificate. Some of the main ways to obtain an X.509 certificate include:

#1. Generating a self-signed certificate

Getting a self-signed certificate involves generating your own X.509 certificate on your machine. This is done using tools such as OpenSSL installed and used to generate self-signed certificates. However, self-signed certificates are not ideal for production use because of being self-signed with no reliable third party to verify a user’s identity

#2. Obtain a free X.509 certificate

There are public certificate authorities that issue users with free X.509 certificates. An example of such a non-profit organization is Let’s Encrypt, backed by companies like Cisco, Chrome, Meta, and Mozilla, among many others. Let’s Encrypt, a certificate authority that issues X.509 certificates for free, has so far issued certificates to over 300 million websites.

#3. Purchase an X.509 certificate

There are also commercial certificate authorities that sell X.509 certificates. Some of these companies include DigiCert, Comodo, and GlobalSign. These companies offer different types of certificates at a fee.

#4. Certificate signing request (CSR)

a Certificate Signing Request(CSR)  is a file that contains all the information about an organization, website, or domain. This file is then sent to a Certificate Authority for signing. Once the certificate authority signs the CSR, it can be used to create an X.509 certificate for the entity that sent the CSR.

There are different ways of obtaining X.509 certificates. To determine the best method to obtain an X.509 certificate, consider where it is going to be used and what application is going to use the X.509 certificate.

Final Words

In a world where data breaches are common and cyber attacks such as man-in-the-middle attacks are prevalent, it is important to secure your data through digital certificates such as X.509 certificates.

This not only ensures that sensitive information does not fall into the wrong hands but also establishes trust among communicating parties allowing them to work with the assurance that they are dealing with authorized parties and not malicious actors or intermediaries.

It is easy to build trust with those you’re communicating with if you have a digital certificate that proves your true identity. This is important in any transaction that happens over the internet.

  • Collins Kariuki
    Collins Kariuki is a software developer and technical writer for Geekflare. He has over four years experience in software development, a background in Computer Science and has also written for Argot, Daily Nation and the Business Daily Newspaper.
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