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Using a command line website downloader, such as wget, curl or any other one... In a script...

I have the SHA-1 and the SHA-256 certficate fingerprint of a website. Due to security concerns (1) (2), I don't want to use the public SSL certificate authority system. The fingerprint must be hard coded.

Can a wget like application check the SSL fingerprint?

wget does not have such a functionality. (3)

Using wget --ca-certificate or curl --cacert I would have to run my own local certificate authority, which I'd like to prevent, because that adds a lot complexity. It's also ultra difficult and no one did that ever before. (4)

Isn't there any tool, like
download --tlsv1 --serial-number xx:yy:zz --fingerprint xxyyzz https://site.com?

The solution must of course not be vulnerable to TOCTOU. (5) The MITM could let return a valid fingerprint for the openssl client request and tamper with the following wget request.

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6 Answers 6

Reset to default
34

Source

Install required software:

apt-get install ca-certificates curl

Download the public SSL certificate:

openssl s_client -connect torproject.org:443 -CAfile /usr/share/ca-certificates/mozilla/DigiCert_Assured_ID_Root_CA.crt >./x.cert </dev/null

Or better:

echo -n | openssl s_client -connect torproject.org:443 -CAfile /usr/share/ca-certificates/mozilla/DigiCert_Assured_ID_Root_CA.crt | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > ./torproject.pem

Get SHA-1 fingerprint:

openssl x509 -noout -in torproject.pem -fingerprint -sha1

Get SHA-256 fingerprint:

openssl x509 -noout -in torproject.pem -fingerprint -sha256

Manually compare SHA-1 and SHA-256 fingerprints with torproject.org FAQ: SSL.

.

Optionally render the ca-certificates useless for testing purposes. Using curl here, but wget has a bug Bug and uses the ca-files anyway.

sudo mv /usr/share/ca-certificates /usr/share/ca-certificates_

Download with curl and the pinned certificate:

curl --cacert ./torproject.pem https://check.torproject.org/ > check.html
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  • this doesn't work in the presence of a proxy, though :-/
    – Frederick Nord
    Apr 16, 2015 at 9:00
  • Please note that the -CAfile option is completely ignored in your example.
    – Lars
    Feb 20, 2018 at 16:13
13

In tcsh:

echo | openssl s_client -connect host.example.com:443 |& openssl x509 -fingerprint -noout
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2
  • 3
    works in zsh, should work for bash too
    – number5
    Jan 22, 2016 at 0:22
  • What does the & character after the pipe?
    – SamK
    Jan 16, 2023 at 15:38
10

This is also enough:

openssl x509 -fingerprint -in server.crt
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1
  • Add -md5 option to retrieve MD5 Fingerprint. -md5 must not put in between -in and server.crt.
    – 林果皞
    Jul 30, 2018 at 14:35
4

This is fairly easy to do with the openssl command and its client functionality.

The following little script will take a given domain (no https prefix) and an SHA-1 fingerprint, and exit with no error (0) if the retrieved fingerprint matches, but with exit code 1 if there is no match. You can then incorporate it into your script by simply testing the last exit code $?:

#!/bin/bash

FPRINT=`echo -n | openssl s_client -connect $1:443 2>/dev/null \|
        openssl x509  -noout -fingerprint | cut -f2 -d'='`

if [ "$2" = "$FPRINT" ]; then
    exit 0
  else
    exit 1
fi
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3
  • 1
    It's vulnerable to TOCTOU. [1] The MITM could let return a valid fingerprint for the openssl client request and tamper with the following wget request. [1] en.wikipedia.org/wiki/Time_of_check_to_time_of_use
    – James Mitch
    Sep 14, 2012 at 11:30
  • True, in theory. It would be fairly easy to modify wget and compile it with OpenSSL so that it performs what you want inline, but that is beyond the scope of an AU answer.
    – ish
    Sep 14, 2012 at 12:19
  • So, how about using s_client to also retrieve the document? Something like (echo -ne "Host: ${HOST}\n\rGET ${URL}\n\r" && yes) 2>/dev/null | openssl s_client -connect ${HOST}:443 should work, no? Well, you have to split the SSL session info from the actual content reply.
    – taneli
    Sep 17, 2012 at 11:10
3

source

#!/usr/bin/perl
# https://security.stackexchange.com/questions/20399/how-to-verify-the-ssl-fingerprint-by-command-line-wget-curl
# Code snippets taken from Net::SSLeay documentation and mildly modified.
# Requires a newer version of SSLeay (tested with 1.48)
# Needless to say, verify correct $host and $fingerprint before testing!!!

use Net::SSLeay qw(get_https3);

$host = "www.google.com";
$port = 443;
$fingerprint = "C1:95:6D:C8:A7:DF:B2:A5:A5:69:34:DA:09:77:8E:3A:11:02:33:58";

($p, $resp, $hdrs, $server_cert) = get_https3($host, $port, '/');
if (!defined($server_cert) || ($server_cert == 0)) {
    warn "Subject Name: undefined, Issuer  Name: undefined";
} elsif (Net::SSLeay::X509_get_fingerprint($server_cert, "sha1") ne $fingerprint) {
    warn 'Invalid certificate fingerprint '
        .  Net::SSLeay::X509_get_fingerprint($server_cert, "sha1")
        . ' for ' . Net::SSLeay::X509_NAME_oneline(
             Net::SSLeay::X509_get_subject_name($server_cert));
} else {
    print $p;
}

As is outlined in the Net::SSLeay documentation, this method means verification after the HTTP transaction, and so should not be used if you want to verify you're talking to the right server before sending them data. But if all you're doing is deciding whether or not to trust what you just downloaded (which is sounds like you are from your reference #4) this is fine.

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2

That's my everyday script:

curl --insecure -v https://www.google.com 2>&1 | awk 'BEGIN { cert=0 } /^\* Server certificate:/ { cert=1 } /^\*/ { if (cert) print }'

Ouput:

* Server certificate:
*    subject: C=US; ST=California; L=Mountain View; O=Google Inc; CN=www.google.com
*    start date: 2016-01-07 11:34:33 GMT
*    expire date: 2016-04-06 00:00:00 GMT
*    issuer: C=US; O=Google Inc; CN=Google Internet Authority G2
*    SSL certificate verify ok.
* Server GFE/2.0 is not blacklisted
* Connection #0 to host www.google.com left intact
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