Create a self-signed SSL certificate with OpenSSL

• In this post we will explore how to create a self-signed SSL certificate files using OpenSSL

• OpenSSL is a toolkit for cryptography

What is a self-signed certificate

• A self-signed certificate is a digital certificate that is signed by its own creator, rather than a trusted third-party Certificate Authority (CA). They are often used in development and testing environments where CA is not necessary

• The following files will be generated for a self-signed certificate

  • cert.pem - Certificate file. This contains the public key, certificate information like subject, department, Organizational unit, country etc.

  • key.pem - encrypted private key file. This contains the private key

  • certificate.pfx - contains both certificate and private key information in a single file

Install OpenSSL

• OpenSSL can be downloaded for windows at https://slproweb.com/products/Win32OpenSSL.html

• OpenSSL also comes in-built with git bash

• OpenSSL can be installed in debian linux operating systems using the following commands

sudo apt update

sudo apt install openssl  libssl-dev

Certificate and private key files generation

Command for Interactive mode

• Upon running the following command, the files cert.pem and key.pem are generated after answering the questions by openssl.

openssl req -x509 -newkey rsa:4096 -keyout  key.pem -out cert.pem -sha256 -days 365

Command for Non-interactive and 10 years expiration

openssl req -x509 -newkey rsa:4096 -keyout  key.pem -out cert.pem -sha256 -days 3650 -nodes -subj "/C=XX/ST=StateName/L=CityName/O=CompanyName/OU=CompanySectionName/CN=CommonNameOrHostname"

Create pfx file from certificate and key files

• The following command creates the pfx file (certificate.pfx) from key.pem and cert.pem files

openssl pkcs12 -export -out certificate.pfx -inkey  key.pem -in cert.pem

Check PFX contents:

• Run the following command to check if the pfx file is valid and the contents of pfx file

openssl pkcs12 -info -in certificate.pfx

References

• OpenSSL download for windows - https://slproweb.com/products/Win32OpenSSL.html

• OpenSSL docs - https://docs.openssl.org/master/man1/