How to verify SSL SHA-1 Certificate Fingerprnit Signature of your mail/web server to avoid hijacking/man-in-the-middle attacks

This is especially helpful if you run your own servers.  If you are presented with an error message or warning that the signature has changed or does not match the IP/domain you are connecting to you always want to verify manually.

So your e-mail/web client will show you an SHA-1 fingerprint like this:

"Could not verify this certificate because the issuer is unkown" or other reasons such as a mismatch in IP/domain.

It will also show you the "SHA1 fingerprint".   Copy this and compare below with the results of your actual server certificate.

How to verify it against the actual certificate on your server?:

openssl x509 -fingerprint -in /pathto/your-certificate.crt -noout

SHA1 Fingerprint=CD:32:57:8A:66:18:71:87:81:B8:A5:F6:2E:52:3D:15:C5:A9:41:06

How to manually fetch the SHA1 certificate straight from the server to compare?

openssl s_client -showcerts -connect yourdomain.com:port 2>/dev/null|openssl x509 -fingerprint -noout

Automated Bash Script

#!/bin/bash

#change servercertpath to your certificate

servercertpath=/etc/ssl/key.crt

#remote host

#change remote host/ip and port number as necessary

remotehost="realtechtalk.com:443"

localfingerprint=`openssl x509 -fingerprint -in $servercertpath -noout`

#the echo -e \n prints a newline to the SSL client this is necessary or it will never exit so the script will halt and not complete

remotefingerprint=`echo -e "\n"|openssl s_client -showcerts -connect $remotehost 2>/dev/null|openssl x509 -fingerprint -noout`

if [ "$localfingerprint" == "$remotefingerprint" ]; then

echo "OK - Certs match: local=$localfingerprint remote=$remotefingerprint"

else

echo "BAD - Certs don't match could be man in the middle!: local=$localfingerprint remote=$remotefingerprint"

fi

 

Conclusion

This is an important and good way to verify that you are actually talking to who you think you are and that there is no direct interception or Middleman attack.


Tags:

verify, ssl, sha, certificate, fingerprnit, server, hijacking, attacksthis, servers, presented, ip, domain, connecting, manually, fingerprint, quot, issuer, unkown, mismatch, openssl, pathto, crt, noout, fetch, s_client, showcerts, yourdomain, dev, null, automated, bash, bin, servercertpath, etc, remotehost, realtechtalk, localfingerprint, echo, newline, halt, remotefingerprint, ok, certs, fi, interception, middleman,

Latest Articles

  • CentOS 6 impossible to compile a newer libguestfs
  • chroot
  • How To Get Started on Ubuntu with gpt-2 OpenAI Text Prediction
  • Remove cloud-init in your VM
  • QEMU-KVM KVM Command Line Practical Guide
  • Linux How To Change NIC Name to eth0 instead of enps33 or enp0s25
  • virt-resize: error: libguestfs error: could not create appliance through libvirt.
  • Asterisk Does Not Retry When Authentication Fails
  • Linux Debian Ubuntu How To Install PEPPER Faster and Latest Adobe Flash Player in Firefox
  • How To Speed Up Linux Ubuntu and Debian Based Computers By Improving CPU Performance and Changing the CPU Governor
  • Convert data or file to base64 on a single line
  • Linux Mint Ubuntu Debian radeon slow 2D performance issues radeon_dp_aux_transfer_native: 158 callbacks suppressed
  • mdadm: super0.90 cannot open /dev/sdb1: Device or resource busy mdadm: /dev/sdb1 is not suitable for this array.
  • How To Install NextCloud on Centos 7 and Centos 8
  • AH01630: client denied by server configuration:
  • ERROR: Could not find a version that satisfies the requirement PIL (from versions: none) ERROR: No matching distribution found for PIL
  • ZTE Camera Cannot Work unable to connect to camera. Camera has been disabled becaue of security policies or is being used by other apps
  • QEMU KVM how to boot off a physical CD/DVD/BDROM Drive
  • How To Install OpenProject on Centos 7 Step-by-Step Guide
  • Ubuntu Debian Linux Cannot Install Wine Solution - wine1.6 : Depends: wine1.6-i386 (= 1:1.6.2-0ubuntu14.2) but it is not installable wine1.4 : Depends: wine1.6 but it is not going to be installed