tldr/pages/common/openssl.md

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# openssl
> OpenSSL cryptographic toolkit.
> More information: <https://www.openssl.org>.
- 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 certificate information:
`openssl x509 -in {{filename.crt}} -noout -text`
- Display a certificate's expiration date:
`openssl x509 -enddate -noout -in {{filename.pem}}`
- 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`