Command
openssl
Explanation
OpenSSL is a cryptographic library providing SSL/TLS encryption and certificate management.
Examples
Generate self-signed certificate
openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout key.pem
View certificate details
openssl x509 -in cert.pem -text -noout
Test SSL connection
openssl s_client -connect example.com:443