tldr/pages/common/openssl.md

openssl

OpenSSL cryptographic toolkit.

• Generate a 2048bit RSA private key and save it to a file:

openssl genrsa -out {{filename.key}} 2048

• Generate a certificate signing request to be sent to a certificate authority:

openssl req -new -sha256 -key {{filename.key}} -out {{filename.csr}}

• Generate a self-signed certificate from a certificate signing request valid for some number of days:

openssl x509 -req -days {{days}} -in {{filename.csr}} -signkey {{filename.key}} -out {{filename.crt}}

• Display the start and expiry dates for a domain's certificate:

openssl s_client -connect {{host}}:{{port}} 2>/dev/null | openssl x509 -noout -dates

• Display the certificate presented by an SSL/TLS server:

openssl s_client -connect {{host}}:{{port}} </dev/null

• Display the complete certificate chain of an HTTPS server:

openssl s_client -connect {{host}}:443 -showcerts </dev/null