OpenSSL is a cryptography toolkit.
openssl s_client -connect {{domain}}:{{port}}
openssl req -out {{path/to/CSR.csr}} -new -newkey rsa:2048 -nodes -keyout {{path/to/pivate.key}}
openssl x509 -text -noout -in {{path/to/certificate.crt}}
openssl rsa -check -in {{path/to/pivate.key}}
openssl req -text -noout -verify -in {{path/to/CSR.csr}}
openssl x509 -noout -modulus -in {{path/to/certificate.crt}} | openssl md5
openssl rsa -noout -modulus -in {{path/to/pivate.key}} | openssl md5
openssl req -noout -modulus -in {{path/to/CSR.csr}} | openssl md5