CA Self-Signed Certificates: A Guide

TL;DR

A Certification Authority (CA) can self-sign a certificate, but it’s generally not recommended for production environments. It’s useful for testing and internal systems where trust is pre-established. Browsers won’t automatically trust these certificates.

Understanding the Issue

A CA normally signs certificates for other entities (like websites). This signature verifies that the certificate is legitimate. When a CA self-signs, it’s essentially vouching for its own identity. The problem is that most devices and browsers don’t inherently trust any CA; they rely on a list of trusted root CAs.

Steps to Create a Self-Signed Certificate

1. Generate a Private Key: This key must be kept secure!

openssl genrsa -out ca.key 2048

2. Create a Certificate Signing Request (CSR): The CSR contains information about the CA.

openssl req -new -key ca.key -out ca.csr

You’ll be prompted for details like country, organisation name etc. Fill these in accurately.

3. Self-Sign the Certificate: Use the private key to sign the CSR, creating the self-signed certificate.

openssl x509 -req -days 365 -in ca.csr -signkey ca.key -out ca.crt

The -days 365 option sets the validity period to one year. Adjust as needed.

4. Verify the Certificate: Check that the certificate was created correctly.

openssl x509 -in ca.crt -text -noout

This will display the certificate details, including the issuer (which should be the same as the subject in this case).

Why Self-Signed Certificates Aren’t Ideal for Public Use

• Trust Issues: Browsers and operating systems won’t automatically trust a self-signed certificate. Users will see security warnings.
• Man-in-the-Middle Risks: Without external validation, it’s easier for attackers to create fake certificates.
• Not Suitable for Public Websites: Publicly trusted CAs are required for secure e-commerce and other sensitive applications.

When Self-Signed Certificates Are Useful

• Internal Testing: For testing purposes within a controlled environment.
• Development Environments: When you need HTTPS locally without the hassle of obtaining a public certificate.
• Private PKI: In some organisations, a private Public Key Infrastructure (PKI) uses self-signed root certificates for internal services. The CA certificate is distributed to all clients beforehand.

Adding a Self-Signed Certificate to a Trusted Store (For Testing Only!)

Warning: This weakens security and should only be done in testing environments.

• Chrome/Edge: Go to Settings > Privacy and Security > Manage Certificates. Import the ca.crt file into the Trusted Root Certification Authorities store.
• Firefox: Go to Options > Privacy & Security > View Certificates. Import the ca.crt file, and trust it for identifying websites.