How to get and use the Root CA Certificate Fingerprint in the Elastic Stack

July 2022

Latest developments in Beats, Elastic Agent and Logstash now include a new parameter that makes easier to trust a self-signed certificate, we would just need A HEX encoded SHA-256 of a CA certificate.

Getting the fingerprint from a server

We can get this fingerprint by simply using openssl and connecting to the server you want to extract the fingerprint:

openssl s_client \
  -connect \
  -servername \
  -showcerts < /dev/null 2>/dev/null | \
  openssl x509 -in /dev/stdin -sha256 -noout -fingerprint | \
  sed 's/://g'  

Getting the fingerprint from a file

if you have an actual certificate file for the CA you can just load it:

 openssl x509 -in ca_file.pem -sha256 -fingerprint | grep SHA256 | sed 's/://g'

The response will be something like

SHA256 Fingerprint=65C080BF18DBFA8F57606DBA0ED11D32DF42CF63B55CC07C7A764AA9597A9403

So you can use this fingerprint in output.elasticsearch:

  hosts: ...
  api_key: ...
  index: ...
  ssl.ca_trusted_fingerprint: "65C080BF18DBFA8F57606DBA0ED11D32DF42CF63B55CC07C7A764AA9597A9403"
  ssl.verification_mode: full