Certutil

Certutil is a cli to help you to easily look inside certificates and debug issues.

Motivation

I got tired of googling for openssl commands and wanted something simple and easy to use with a memorable cli.

Usage

Install with go get

$ go get github.com/jsws/certutil

Info

info will print out certificate information in an easily readable format. It will also perform AIA fetching.

$ certutil info connect github.com
Connecting to github.com:443
Connected to 140.82.121.4:443
Recieved 2 certificate(s).

Certificate 0
  Subject: CN=github.com,O=GitHub\, Inc.,L=San Francisco,ST=California,C=US
  Issuer:  CN=DigiCert SHA2 High Assurance Server CA,OU=www.digicert.com,O=DigiCert Inc,C=US
  DNS Names: github.com, www.github.com
  Vailidity Period
      Not Before:  2020-05-05 00:00:00 +0000 UTC ✅
      Not After:   2022-05-10 12:00:00 +0000 UTC ✅

Certificate 1
  Subject: CN=DigiCert SHA2 High Assurance Server CA,OU=www.digicert.com,O=DigiCert Inc,C=US
  Issuer:  CN=DigiCert High Assurance EV Root CA,OU=www.digicert.com,O=DigiCert Inc,C=US
  Vailidity Period
      Not Before:  2013-10-22 12:00:00 +0000 UTC ✅
      Not After:   2028-10-22 12:00:00 +0000 UTC ✅

Certificate is valid 🔒

Save

save will save the certificates presented by a server to a file in PEM format. The file to the save the PEM chain in is given with the --output or -o flag. If no output file is set the PEM encoded certificate is outputted to stdout.

$ certutil save connect github.com -o file.pem
Connecting to jsws.co.uk:443
Connected to 185.199.111.153:443
Recieved 2 certificate(s).
Saving to file.pem

$ certutil save connect github.com
Connecting to github.com:443
Connected to 140.82.121.3:443
Recieved 2 certificate(s).
-----BEGIN CERTIFICATE-----
...

Connect

The connect subcommand can be used with the info and save command to connect to a server presenting TLS certificates. The --servername or -s flag can be used to set the SNI.

Read

The read subcommand can be used with the info command to display certificate information from a local PEM encoded certificate file. The path of the file is given as an argument.

$ certutil info read certs/file.pem

Limitations

info.IsValid() shouldn't be used for anything important as it doesn't do revocation checking or certificate transparency checking.

TODO:

• Ability to show full cert chain when AIA fetching is used.
• Add verbose output for AIA
• Add revocation checking