OpenSSL tricks

Download a site's certificate.

This command will connect to example.com on port 443 using the s_client subcommand and output the site's certificate information in text format using the x509 subcommand. The -text option tells openssl to print the certificate information in human-readable text format, while the -noout option tells it not to output the certificate itself.

You can replace example.com with the hostname or IP address of the site you want to get the certificate for. The < /dev/null part of the command is used to prevent the s_client command from waiting for input.

openssl s_client -connect example.com:443 < /dev/null | openssl x509 -text -outform PEM > /path/to/cert.cer