whichca

README

This is a utility for

• Verifying a website presents enough information to validate a chain of trust
• Failing said verification, determine which intermediate certs (if any) could be added to the CA bundle to get it to a verified chain
• Can be used to download a CA bundle from the web (defaults to curl.se's mozilla bundle)
• Can determine what the minimum CA bundle a client would need to verify a site / list of sites or certificate bundle files.
• Can dump the system's default CA bundle (see limitations below)

Usage:

Subcommands:

check

This is to check a site or a pem certificate file to see if it is trusted against either the system default CA bundle (default) or a CA bundle file specified with the -ca option. This will also provide an option to dump any missing intermediates needed to correct the configuration.

(njohnson@greyeagle:~)% whichca check -hp google.com:443 -hp bing.com:443
*.google.com is good!
www.bing.com is good!
(njohnson@greyeagle:~)%

fetchca

This is to download and (optionally) verify a PEM CA bundle from a remote website . It defaults to the mozilla PEM bundle provided by curl.se. Please don't script this in such a way that it downloads the file more than once a day, but since I actually default to stdout I don't have a good way to check file age and do any attempt to enforce this.

(njohnson@greyeagle:~)% whichca fetchca -out ca.pem
verified 129 certificates in bundle downloaded from https://curl.se/ca/cacert.pem
(njohnson@greyeagle:~)%

Note this verification is only that the certificates are parsable and valid.

minca

This is a command for determining the minimum CA bundle needed to validate a list of certificate bundles or websites.

For a local certificate bundle:

whichca minca -p /path/to/cert/bundle.crt

or for a remote certificate at a given hostname:port

whichca minca -hp host.whatever.com:443

If all goes well, it will spit out the PEM encoded version of the chain leading to the root certificate, minus the certificate and intermediates found in the cert bundle(s) passed.

dumpca

Additionally, on platforms that aren't Windows-based, it can be used to get a full dump of the default system certificate bundle, with the following:

whichca dumpca

On macOS this uses the security find-certificate -ap utility, which is what golang did under the covers until recently when they decided to defer to the darwin keychain api for verification. There are some caveats here, one being that the darwin keychain is more lax than the golang x509 parser, so some certs in the keychain might not get parsed correctly by golang. In the case it finds one of these, it will print the certificate in PEM form on stderr with a warning in the comments. See here for details. All verified certificates will be printed on stdout. On other *nix platforms, this calls x509.SystemCertPool and does some reflect nastiness to ferret out the certs.

Flags

You can mix and match host:port and pathspec definitions on the same command, specifying any number of each

For example, this is valid:

whichca minca -hp host.whatever.com:443,host2.whatever.com:443 -p '/path/to/*.crt' -p ./mycert.crt

Note the single quotes around the wildcard above. This is necessary to keep the shell from intercepting the wildcard character.

To install, download a release binary from the releases page on github (preferred), or to install from source simply:

go install github.com/nathanejohnson/whichca@latest