In short: nothing that openSSL can't do, just a few easy shortcuts (without needing openSSL) and colourised output.
Binaries can be found at releases or retrieved with go.
go get github.com/nxadm/certmin
$ ./certmin
certmin, 0.4.2. A minimalist certificate utility.
See https://github.com/nxadm/certmin for more information.
Usage:
certmin skim cert-location1 [cert-location2...]
[--remote-chain] [--remote-inters] [--no-colour]
certmin verify-key cert-location key-file [--no-colour]
certmin verify-chain cert-location [cert-location2...]
[--remote-chain] [--remote-inters]
[--root=ca-file1 --root=ca-file2...]
[--inter=inter-file1 --inter=inter-file2...]
[--no-colour]
certmin [-h]
certmin [-v]
Certificate locations can be a file, a string in the form of
hostname:port (default 443 if not :port supplied) or an URL.
When verifying a chain, the OS trust store will be used if
if no roots certificates are given or requested.
Actions:
skim | sc : skim PEM certificates (including bundles)
and show information.
--remote-chain : retrieve the chain (if offered) for
remote certificates.
verify-key | vk : verify that a PEM certificate and
key match.
verify-chain | vc : verify that a PEM certificate matches its
chain.
--remote-chain : retrieve the chain (if offered) for
remote certificates.
--remote-inters : retrieve the chain (if offered) for
remote certificates, without root CAs.
--root : root PEM certificate file to verify.
against (optional).
--inter : intermediate PEM certificates files
to verify against (optional).
Global options:
--no-colour | -c : don't colourise the output'
--help | -h : this help message.
--version | -v : version message.
$ ./certmin skim t/chain.crt
certificate location t/chain.crt:
Subject: CN=AAA Certificate Services,O=Comodo CA Limited,L=Salford,ST=Greater Manchester,C=GB
Issuer: CN=AAA Certificate Services,O=Comodo CA Limited,L=Salford,ST=Greater Manchester,C=GB
Serial number: 1
Version: 3
Public key algorithm: RSA
Signature algorithm: SHA1-RSA
CRL locations: http://crl.comodoca.com/AAACertificateServices.crl, http://crl.comodo.net/AAACertificateServices.crl
Not before: 2004-01-01 00:00:00 +0000 UTC
Not after: 2028-12-31 23:59:59 +0000 UTC
Subject: CN=USERTrust RSA Certification Authority,O=The USERTRUST Network,L=Jersey City,ST=New Jersey,C=US
Issuer: CN=AAA Certificate Services,O=Comodo CA Limited,L=Salford,ST=Greater Manchester,C=GB
Serial number: 76359301477803385872276235234032301461
Version: 3
Is CA: true
Public key algorithm: RSA
Signature algorithm: SHA384-RSA
OCSP servers: http://ocsp.comodoca.com
CRL locations: http://crl.comodoca.com/AAACertificateServices.crl
Not before: 2019-03-12 00:00:00 +0000 UTC
Not after: 2028-12-31 23:59:59 +0000 UTC
Subject: CN=GEANT OV RSA CA 4,O=GEANT Vereniging,C=NL
Issuer: CN=USERTrust RSA Certification Authority,O=The USERTRUST Network,L=Jersey City,ST=New Jersey,C=US
Serial number: 290123421899608141648701916708796095456
Version: 3
Is CA: true
Public key algorithm: RSA
Signature algorithm: SHA384-RSA
OCSP servers: http://ocsp.usertrust.com
CRL locations: http://crl.usertrust.com/USERTrustRSACertificationAuthority.crl
Not before: 2020-02-18 00:00:00 +0000 UTC
Not after: 2033-05-01 23:59:59 +0000 UTC
---
$ ./certmin skim github.com --remote-chain
Certificate location github.com:
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
Serial number: 7101927171473588541993819712332065657
Version: 3
Public key algorithm: RSA
Signature algorithm: SHA256-RSA
OCSP servers: http://ocsp.digicert.com
CRL locations: http://crl3.digicert.com/sha2-ha-server-g6.crl, http://crl4.digicert.com/sha2-ha-server-g6.crl
Not before: 2020-05-05 00:00:00 +0000 UTC
Not after: 2022-05-10 12:00:00 +0000 UTC
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
Serial number: 6489877074546166222510380951761917343
Version: 3
Is CA: true
Public key algorithm: RSA
Signature algorithm: SHA256-RSA
OCSP servers: http://ocsp.digicert.com
CRL locations: http://crl4.digicert.com/DigiCertHighAssuranceEVRootCA.crl
Not before: 2013-10-22 12:00:00 +0000 UTC
Not after: 2028-10-22 12:00:00 +0000 UTC
---
$ ./certmin skim smtps://smtp.gmail.com
Certificate location smtps://smtp.gmail.com:
Subject: CN=smtp.gmail.com,O=Google LLC,L=Mountain View,ST=California,C=US
Issuer: CN=GTS CA 1O1,O=Google Trust Services,C=US
DNS names: smtp.gmail.com
Serial number: 257235496908235390426179598999401729070
Version: 3
Public key algorithm: ECDSA
Signature algorithm: SHA256-RSA
OCSP servers: http://ocsp.pki.goog/gts1o1core
CRL locations: http://crl.pki.goog/GTS1O1core.crl
Not before: 2020-12-15 14:48:07 +0000 UTC
Not after: 2021-03-09 14:48:06 +0000 UTC
---
$ ./certmin verify-key t/myserver.crt t/myserver.key
the certificate and key match
$ ./certmin verify-key myserver.com myserver.key
the certificate and key match
$ ./certmin verify-chain t/myserver.crt --root t/ca.crt
certificate CN=myserver and its chain match
$ ./certmin verify-chain github.com:443 --remote-chain
certificate CN=github.com,O=GitHub\, Inc.,L=San Francisco,ST=California,C=US and its chain match
$ ./certmin verify-chain github.com:443 --root ~/tmp/chain.crt
x509: certificate signed by unknown authority
certificate CN=github.com,O=GitHub\, Inc.,L=San Francisco,ST=California,C=US and its chain do not match