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.

Latest Articles

  • Centos 7 - Convert Minimal to Graphical GUI GNOME or KDE Desktop
  • AMD Set Fan Speed and Other Powerplay Memory/CPU Timings with a Linux script
  • Ethereum Mining Claymore Nanopool Error
  • genisoimage errors with long filenames and deep directory structures
  • Linux Kernel USB Export Errors
  • How to download gajim 0.16.9 XMPP/Jabber client so you can use OMEMO encryption
  • HP DL385 G7 Linux BIOS Update Flash
  • hwloc-nox set CPU affinity in Linux
  • Firefox An error occurred during a connection to some-ip-or-domain. SSL peer reports incorrect Message Authentication Code. Error code: SSL_ERROR_BAD_MAC_ALERT Solution
  • Proxmox understanding the directory structure and why an NFS datastore appears to be missing files/isos
  • pandoc convert markdown to html
  • Proxmox error uploading an iso solution
  • Cannot install moodle
  • MySQL change for Antelope format to Barracuda error solution
  • vmkping -I vmk1 10.0.2.69 PING 10.0.2.69 (10.0.2.69): 56 data bytes sendto() failed (Host is down)
  • gvfs mount in /run/user cannot be accessed or displayed wrong permissions
  • VMWare vSphere 6.7 Errors Solution 503 Service Unavailable (Failed to connect to endpoint:
  • How To Enable Nested KVM so guests can virtualize with hardware extensions
  • vi error solution E166: Can't open linked file for writing
  • Supermicro IPMI / KVM / BMC Remote Console Screen Resizing Issue - Window Cut Off Solution