openssl tools

Under Linux and now also under Bash Windows 10 you have tools like OpenSSL. Besides generating certificates, this tool is quite useful for testing your secure site.

For example, the command below will search for all domains in the certificate in case it is a SAN/wildcard certificate.

#openssl s_client -connect google.com:443 | openssl x509 -noout -text | grep DNS:

depth=2 OU = GlobalSign Root CA - R2, O = GlobalSign, CN = GlobalSign
verify return:1
depth=1 C = US, O = Google Trust Services, CN = GTS CA 1O1
verify return:1
depth=0 C = US, ST = California, L = Mountain View, O = Google LLC, CN = *.google.com
verify return:1
                DNS:*.google.com, DNS:*.android.com, DNS:*.appengine.google.com, DNS:*.cloud.google.com, DNS:*.crowdsource.google.com, DNS:*.g.co, DNS:*.gcp.gvt2.com, DNS:*.gcpcdn.gvt1.com, DNS:*.ggpht.cn, DNS:*.gkecnapps.cn, DNS:*.google-analytics.com, DNS:*.google.ca, DNS:*.google.cl, DNS:*.google.co.in, DNS:*.google.co.jp, DNS:*.google.co.uk, DNS:*.google.com.ar, DNS:*.google.com.au, DNS:*.google.com.br, DNS:*.google.com.co, DNS:*.google.com.mx, DNS:*.google.com.tr, DNS:*.google.com.vn, DNS:*.google.de, DNS
*.google.es, DNS:*.google.fr, DNS:*.google.hu, DNS:*.google.it, DNS:*.google.nl, DNS:*.google.pl, DNS:*.google.pt, DNS:*.googleadapis.com, DNS:*.googleapis.cn, DNS:*.googlecnapps.cn, DNS:*.googlecommerce.com, DNS:*.googlevideo.com, DNS:*.gstatic.cn, DNS:*.gstatic.com, DNS:*.gstaticcnapps.cn, DNS:*.gvt1.com, DNS:*.gvt2.com, DNS:*.metric.gstatic.com, DNS:*.urchin.com, DNS:*.url.google.com, DNS:*.wear.gkecnapps.cn, DNS:*.youtube-nocookie.com, DNS:*.youtube.com, DNS:*.youtubeeducation.com, DNS:*.youtubekids.com, DNS:*.yt.be, DNS:*.ytimg.com, DNS:android.clients.google.com, DNS:android.com, DNS:developer.android.google.cn, DNS:developers.android.google.cn, DNS:g.co, DNS:ggpht.cn, DNS
gkecnapps.cn, DNS:goo.gl, DNS:google-analytics.com, DNS:google.com, DNS:googlecnapps.cn, DNS:googlecommerce.com, DNS:source.android.google.cn, DNS:urchin.com, DNS:www.goo.gl, DNS:youtu.be, DNS:youtube.com, DNS:youtubeeducation.com, DNS:youtubekids.com, DNS:yt.be
read:errno=0

Another example is if you want to test your site if it still using SSLv3 for example. (in the case below you see it is not using SSLv3)

#openssl s_client -connect www.google.com:443 -ssl3

139782489835160:error:140A90C4:SSL routines:SSL_CTX_new:null ssl method passed:ssl_lib.c:1878:

You can also test by excluding a protocol and see with what protocol the SSL/TLS sessions are established:

#openssl s_client -connect google.com:443 -no_tls1

SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256

Or you want to see what protocol it is using:

#openssl s_client -connect www.google.com:443  | grep Protocol

depth=2 OU = GlobalSign Root CA - R2, O = GlobalSign, CN = GlobalSign
verify return:1
depth=1 C = US, O = Google Trust Services, CN = GTS CA 1O1
verify return:1
depth=0 C = US, ST = California, L = Mountain View, O = Google LLC, CN = www.google.com
verify return:1
    Protocol  : TLSv1.2

You can also test if a particular cipher is supported by the remote site (in this case you get a handshake failure as this cipher is not supported):

#openssl s_client -connect google.com:443 -no_tls1  -cipher ECDHE-RSA-AES128-SHA256

CONNECTED(00000003)
139831271622296:error:14077410:SSL routines:SSL23_GET_SERVER_HELLO:sslv3 alert handshake failure:s23_clnt.c:769:

About the author

Mihai is a Senior Network Engineer with more than 15 years of experience

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