For example, I want to find out when the certificate for encrypted.google.com expires (i.e. Not After date), and what other domains may use it for authentication (Subject Alternative Names).
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I don't think we need the x509 tag. In 30k+ Q's this the 1st time it's come up, I think for the level of this Q the use of ssl and certificates is plenty. Please correct me if I'm wrong.– slm ♦Dec 11, 2013 at 2:33
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These are all the Q's that contain x509: unix.stackexchange.com/search?q=x509– slm ♦Dec 11, 2013 at 2:40
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On the off chance I asked this Q on meta: meta.unix.stackexchange.com/questions/2565/…– slm ♦Dec 11, 2013 at 2:44
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Looking at answers below, apparently the x509 certificates had little to none to do with the problem.– BraiamDec 12, 2013 at 15:15
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2 Answers
You could simply write it:
openssl s_client -showcerts -connect encrypted.google.com:443 < /dev/null \
2> /dev/null | openssl x509 -noout -enddate
Other options than -enddate can be used to retrieve other fields. -text outputs most of the information.
See also keytool from java:
keytool -printcert -sslserver encrypted.google.com:443
It will print the whole certificate chain if possible (some of the certificate possibly retrieved from the Java certificate store).
answered Dec 10, 2013 at 22:22
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@J.F.Sebastian - I saw no other method in wiki either beyond
-text. wiki.cacert.org/FAQ/subjectAltName. I think what Stephane's provided is your answer.– slm ♦Dec 11, 2013 at 2:56 -
1@slm, note that J.F.Sebastian answered his own question, he was just sharing his nice script to retrieve certificate information in a useful way. I was just mentioning an alternative way to call the
opensslcommand. (generally, you don't need-inasopenssltakes its input from stdin, and you can retrieve (some) individual parameters without having to parse the output of-text). Dec 11, 2013 at 9:57 -
@StephaneChazelas - I hadn't given the other answer a thorough look, since it looked like an awful lot of code, now looking at it I see what you're saying. Thanks.– slm ♦Dec 11, 2013 at 12:49
To print server's certificate as text using openssl:
#!/bin/bash
#
# Show server's certificate in a human-readable form.
#
# Usage: $ show-cert HOST [PORT]
#
exec <&- # close stdin to suppress `read:errno=0` from openssl
exec openssl x509 -noout -text \
-in <(openssl s_client -connect "$1":"${2:-443}" -showcerts)
Or using Python to get output in json format:
#!/usr/bin/env python3
"""Show server's certificate as json.
Usage:
$ %(prog)s HOST [PORT]
"""
import json
import socket
import ssl
import sys
def getcert(addr, timeout=None):
"""Retrieve server's certificate at the specified address (host, port)."""
# it is similar to ssl.get_server_certificate() but it returns a dict
# and it verifies ssl unconditionally, assuming create_default_context does
with socket.create_connection(addr, timeout=timeout) as sock:
context = ssl.create_default_context()
with context.wrap_socket(sock, server_hostname=addr[0]) as sslsock:
return sslsock.getpeercert()
def main(argv):
host = argv[1]
port = int(argv[2]) if len(argv) > 2 else 443
print(json.dumps(getcert((host, port)), indent=2, sort_keys=True))
if __name__ == "__main__":
main(sys.argv)
Example:
$ getcert encrypted.google.com | jq -r '.notAfter, .subjectAltName[][1]'
Mar 20 00:00:00 2014 GMT
*.google.com
*.android.com
*.appengine.google.com
*.cloud.google.com
...
The latest version: getcert.py