182

I want to download the ssl certificate from, say https://www.google.com, using wget or any other commands. Any unix command line? wget or openssl?

246

In order to download the certificate, you need to use the client built into openssl like so:

echo -n | openssl s_client -connect HOST:PORTNUMBER \
    | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > /tmp/$SERVERNAME.cert

That will save the certificate to /tmp/$SERVERNAME.cert.

You can use -showcerts if you want to download all the certificates in the chain. But if you just want to download the server certificate, there is no need to specify -showcerts

echo -n gives a response to the server, so that the connection is released

sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' removes information about the certificate chain and connection details. This is the preferred format to import the certificate into other keystores.

  • 9
    appreciate that you not only gave a good answer, but also a precise explanation. – marco.m Jan 24 '14 at 17:13
  • Does -showcerts show the server/leaf cert too? I thought it only displayed intermediates when that switch was included. – Mike B Apr 30 '14 at 5:56
  • As the answer said, s_client always shows the server cert (if there is one, i.e. the server responds to hello and doesn't choose an anonymous suite). -showcerts shows all the certs received, server cert first then intermediates and/or root. – dave_thompson_085 May 28 '14 at 8:58
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    this doesn't work in the presences of a proxy, though. – Frederick Nord Apr 16 '15 at 9:00
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    This also doesn't work with servers that use SNI (multiple certificates/domains on a single IP-adress). To avoid problems, specify openssl's servername parameter: openssl s_client -connect HOST:PORTNUMBER -servername CN – verhage Dec 9 '16 at 12:30
60

I found the answer. Openssl provides it.

openssl s_client -connect ${REMHOST}:${REMPORT}

  • 2
    also openssl x509 -text <<EOF cert-text EOF to see details of the certificate – mpapis Aug 1 '12 at 5:21
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    sudo rm -f cert.pem && sudo echo -n | openssl s_client -connect localhost:443 | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > ./cert.pem courtesy of serverfault.com/questions/139728/… – pulkitsinghal Feb 19 '13 at 2:50
  • this accomplishes the same and skips the sed hack. – phs Dec 10 '13 at 7:13
  • This just checks one certificate, what if the service is part of a load balanced group of servers, of which each have a different certificate, possibly signed by a different root CA? Or in other words, a mitm attack might let this request go trough to the real site, and then direct other requests to his servers. Are there any ways to check this? And to get a list of all certificates an domain really has? – Jens Timmerman Apr 28 '14 at 10:37
  • @JensTimmerman "Or in other words, a mitm attack might let this request go trough to the real site, and then direct other requests to his servers." That is not possible unless the man-in-the-middle has a valid certificate for the target server (or the client is silly does not check the server certificate). Evidently, if the server sometimes offers a different certificate you can only hope to probably eventually get them all by repeating connection attempts. – David Tonhofer Aug 4 '15 at 16:08
22

The GNUTLS client tool, gnutls-cli, can also make this easy:

gnutls-cli --print-cert www.example.com \
        < /dev/null \
        > www.example.com.certs

The program is designed to provide an interactive client to the site, so you need to give it empty input (in this example, from /dev/null) to end the interactive session.

  • 1
    how would it make gnutls connect through (the system wide configured) https proxy and print the certificate it exchages? – Frederick Nord Oct 26 '15 at 9:55
9

based on @bignose answer, here is a self-contained version that fits well in e.g. a chef recipe:

sudo apt-get install gnutls-bin 
gnutls-cli --print-cert myserver.com </dev/null| sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > myserver.crt
sudo cp myserver.crt /usr/local/share/ca-certificates/myserver.crt
sudo update-ca-certificates
6
true | openssl s_client -connect google.com:443 2>/dev/null | openssl x509

this mode of openssl expects stdin, so we provide it via true |, this connects to the server specified in the -connect parameter. 2>/dev/null silences errors (optional), we can pass the whole output into the x509 parser, specifying /dev/stdin to use the shell pipe as the input file. And that will output just the -----BEGIN CERTIFICATE----- to -----END CERTIFICATE----- portion of the s_client output. You can redirect that to a file by adding > google.com.pem to the end of the command.


As best I can tell, this does not verify the certificate chain, it only can tell you what ssl identity the end server provides.

  • 2
    (1) this doesn't really improve the answers from 6 years ago (2) x509 reads stdin by default so -in /dev/stdin is redundant (3) s_client verifies the server cert correctly chains to a local trust anchor (root) and is unexpired, but you've suppressed the information that would show this (4) it does NOT check for revocation (5) it checks the name in the server cert only in 1.0.2 and then not by default (but you can easily check that yourself by looking at the cert afterward) – dave_thompson_085 Aug 11 '16 at 21:43
  • @dave_thompson_085, the question is how to download certificate, but not show chain information. I like the openssl x509 much better than sed in another answer. – Der_Meister Feb 22 '18 at 11:49
0

Alternative syntax using Ex and process substitution:

ex +'/BEGIN CERTIFICATE/,/END CERTIFICATE/p' <(echo | openssl s_client -showcerts -connect example.com:443) -scq > file.crt

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