Digital certificates are essential for secure digital communication, particularly for encryption, authentication, and integrity. These certificates are based on Public Key Infrastructure (PKI) and are issued by Certificate Authorities (CAs). Here’s an overview of the main types of certificates and their purposes:

SSL/TLS Certificates #

Used to secure communication between web servers and browsers (HTTPS). Types:

Domain Validation (DV) #

• Validates domain ownership only.
• Fast and inexpensive.

Example: personal websites or blogs.

Organization Validation (OV) #

• Validates domain ownership and organization identity.
• Better trust level, used for small to medium businesses.

Extended Validation (EV) #

• Most rigorous verification of identity and legal existence.
• Shows company name in the address bar (in some browsers).

Example: banking and e-commerce sites.

Wildcard Certificates #

• Secure a domain and all its subdomains (e.g., *.example.com).

Multi-Domain (SAN/UCC) Certificates #

• Secure multiple fully qualified domain names with one certificate.

Code Signing Certificates #

Used by developers to digitally sign software, ensuring the code hasn’t been altered or tampered with after signing.

• Standard Code Signing – Verifies the publisher and ensures code integrity.
• EV Code Signing – Adds stricter verification, and helps avoid Windows SmartScreen warnings.

Email Certificates (S/MIME) #

Used to digitally sign and encrypt email messages.

• Ensures authenticity of sender.
• Prevents eavesdropping and spoofing.

Example: corporate email communications, legal or medical data.

Client Certificates #

Used to authenticate clients (users or devices) to servers.

• Works like a user password, but with stronger cryptography.
• Common in VPNs, secure APIs, mTLS, and enterprise networks.

Root and Intermediate Certificates #

Part of the certificate trust chain:

• Root Certificate – Top-level certificate trusted by systems (pre-installed in OS/browsers).
• Intermediate Certificate – Issued by root, used by CAs to issue end-entity certificates.

This chain of trust allows browsers to verify a website’s certificate by following the path back to a trusted root.

Self-Signed Certificates #

Created and signed by the same entity.

• Used in internal systems or development environments.
• Not trusted by default (cause warnings in browsers).

Comparison Table of Digital Certificate Types #

Certificate Type	Purpose	Identity Validation	Common Use Case	Trusted by Browsers
DV SSL	Secure websites (basic HTTPS)	Domain only	Blogs, personal sites	Yes
OV SSL	Secure websites (verified org)	Domain + Org	Business websites	Yes
EV SSL	High-trust secure websites	Domain + Legal Org	Banks, e-commerce	Yes
Wildcard SSL	Secure all subdomains	Varies	Large websites with many subdomains	Yes
SAN / UCC	Secure multiple domains	Varies	Multi-site hosting, Exchange servers	Yes
Code Signing	Sign software/code	Org or Individual	Software publishers	Not browser-based
EV Code Signing	Sign code with SmartScreen support	Extended Org check	Enterprise software vendors	Not browser-based
S/MIME Email	Secure email (sign/encrypt)	Email + Identity	Corporate and legal email	With config
Client Auth	Authenticate users/devices	Client identity	VPN, APIs, internal apps	Not browser-based
Root Certificate	Trust anchor for CA hierarchy	N/A (pre-installed)	Trusted CAs (e.g., DigiCert, Let’s Encrypt)	Yes
Intermediate Cert	Link root and end-entity certs	Issued by root CA	CA-managed issuance	Yes
Self-Signed Cert	Local/development use	None (self-issued)	Dev, internal testing	No

Trust Chain Diagram #

+----------------------------+
|     Trusted Root CA       |
| (Pre-installed in systems)|
+------------+--------------+
             |
             v
+----------------------------+
|  Intermediate CA (1..n)   |
| (Issued by Root CA)       |
+------------+--------------+
             |
             v
+----------------------------+
|  End-Entity Certificate    |
| (Website, client, email)   |
|  - DV, OV, EV, etc.        |
+----------------------------+

Browsers/clients validate the chain from leaf → intermediate → root.

For example, when visiting https://relianoid.com:

• The browser receives the end-entity cert.
• It checks that it’s signed by a known intermediate.
• Then it ensures that intermediate is trusted via a root CA.