Understanding Self-Signed Certificates and Certificates Signed by a Certificate Authority (CA)

In the world of cybersecurity and encryption, certificates play a pivotal role in securing communications between systems. While there are multiple ways to generate and use certificates, understanding the difference between self-signed certificates and those signed by a Certificate Authority (CA) is essential for choosing the right approach for your needs.

This blog will walk you through the processes of generating both types of certificates, comparing their differences, and clarifying when to use each method.

What is a Self-Signed Certificate?

A self-signed certificate is a certificate where the issuer (the entity that signs the certificate) is the same as the subject (the entity the certificate is issued for). Essentially, you act as your own Certificate Authority.

Steps to Create a Self-Signed Certificate

1. Generate a Private Key

The private key is the foundation of the certificate. It is used to encrypt and decrypt data securely.

openssl genrsa -out private.key 2048        

• This command generates a 2048-bit private key and saves it as private.key.

2. Generate the Certificate

Using the private key, you create a certificate that is self-signed.

openssl req -x509 -new -key private.key -days 365 -out cert.crt -subj "/C=BD/ST=Dhaka/L=Dhaka/O=YourOrg/CN=example.com"        

• -x509: Indicates that this is a self-signed certificate.
• -days 365: Specifies the certificate’s validity (1 year in this case).
• -subj: Provides details such as country (C), state (ST), locality (L), organization (O), and common name (CN).

3. Verify the Certificate

You can inspect the certificate to ensure it has been generated correctly.

openssl x509 -in cert.crt -text -noout        

• This command displays the certificate’s details in a readable format.

What is a Certificate Signed by a Certificate Authority (CA)?

A Certificate Authority (CA) acts as a trusted third party that issues certificates to verify the identity of servers, systems, or users. In this setup, the CA signs server certificates, and clients trust certificates signed by the CA.

Steps to Create a Certificate Authority and Sign Certificates

Step 1: Generate the CA Private Key

The CA’s private key is used to sign other certificates.

openssl genrsa -out ca.key 2048        

• This command generates a private key for the CA.

Step 2: Generate the CA Certificate

Using the private key, create a self-signed certificate for the CA itself.

openssl req -x509 -new -key ca.key -days 1024 -out ca.crt -subj "/C=BD/ST=Dhaka/L=Dhaka/O=YourOrg/CN=YourCA"        

• This creates the CA’s certificate (ca.crt), which will be used to sign other certificates.

Step 3: Generate the Server Private Key

Create a private key for the server.

openssl genrsa -out server.key 2048        

Step 4: Generate a Certificate Signing Request (CSR)

A CSR contains the server’s details and public key. It is sent to the CA for signing.

openssl req -new -key server.key -out server.csr -subj "/C=BD/ST=Dhaka/L=Dhaka/O=YourOrg/CN=example.com"        

• The CSR (server.csr) is generated using the server’s private key.

Step 5: Sign the Server Certificate with the CA

Use the CA’s certificate and private key to sign the server’s CSR.

openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out server.crt -days 500 -sha256        

• This command produces the server’s signed certificate (server.crt).

Step 6: Verify the Server Certificate

Check the signed certificate to confirm its details.

openssl x509 -in server.crt -text -noout        

• This command verifies the server’s certificate.

Comparison: Self-Signed vs. CA-Signed Certificates

When to Use Each Method

Use a Self-Signed Certificate When:

• You need a certificate quickly for internal testing.
• You are securing a single application or server.
• Trust is managed manually, and clients don’t need automatic validation (e.g., local development).

Use a CA-Signed Certificate When:

• You have multiple servers or applications to secure.
• You want a scalable setup with a centralized trust model.
• You are replicating real-world Public Key Infrastructure (PKI) setups for testing.

Conclusion

Both self-signed certificates and CA-signed certificates have their unique purposes. While self-signed certificates are suitable for simple and short-term needs, a CA-signed approach is essential for scalable, secure setups where trust between systems is critical.

Understanding these methods allows you to make informed decisions and implement SSL/TLS encryption effectively in your environments. If you’re working on a complex setup and need guidance, don’t hesitate to explore advanced certificate management techniques or seek professional advice.

Happy encrypting!

Thank you for reading. Here on LinkedIn, I explore how technology shapes the future—covering topics like leadership strategies, career development, and transformative trends such as Cloud Computing, Analytics, Generative AI (GenAI), Machine Learning (ML), and Emerging Tech. If you're as passionate about innovation and progress as I am, hit 'Follow' to stay inspired, and let’s connect on Twitter or Facebook for more ideas and conversations.

Kh. M. Moniruzzaman is an experienced IT and telecom professional, specializing in strategic planning and growth, technology-driven innovation, scalable solution design, and fostering collaboration. Skilled in leveraging advanced technologies such as Generative AI, Kubernetes, serverless computing, and emerging tech, he is dedicated to driving digital transformation, empowering organizations to excel in an ever-evolving technological landscape.

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