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TLS & SSL

Mozilla SL Configuration Generator

https://ssl-config.mozilla.org/

Display the contents of a SSL certificate

For a local file certificate file

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$ openssl x509 -in /usr/share/ca-certificates/mozilla/ISRG_Root_X1.crt  -text
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            82:10:cf:b0:d2:40:e3:59:44:63:e0:bb:63:82:8b:00
        Signature Algorithm: sha256WithRSAEncryption
        Issuer: C = US, O = Internet Security Research Group, CN = ISRG Root X1
        Validity
            Not Before: Jun  4 11:04:38 2015 GMT
            Not After : Jun  4 11:04:38 2035 GMT
        Subject: C = US, O = Internet Security Research Group, CN = ISRG Root X1
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (4096 bit)
                Modulus:
                    00:ad:e8:24:73:f4:14:37:f3:9b:9e:2b:57:28:1c:
                    87:be:dc:b7:df:38:90:8c:6e:3c:e6:57:a0:78:f7:
                    75:c2:a2:fe:f5:6a:6e:f6:00:4f:28:db:de:68:86:
                    ...
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Key Usage: critical
                Certificate Sign, CRL Sign
            X509v3 Basic Constraints: critical
                CA:TRUE
            X509v3 Subject Key Identifier:
                79:B4:59:E6:7B:B6:E5:E4:01:73:80:08:88:C8:1A:58:F6:E9:9B:6E
    Signature Algorithm: sha256WithRSAEncryption
         55:1f:58:a9:bc:b2:a8:50:d0:0c:b1:d8:1a:69:20:27:29:08:
         ac:61:75:5c:8a:6e:f8:82:e5:69:2f:d5:f6:56:4b:b9:b8:73:
         10:59:d3:21:97:7e:e7:4c:71:fb:b2:d2:60:ad:39:a8:0b:ea:
         ...
-----BEGIN CERTIFICATE-----
MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh
cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4
...
-----END CERTIFICATE-----

For a remote website

1
$ openssl s_client -connect ovhcloud.com:443