2 posts

OpenSSL Cheat Sheat

I know I know, there are plenty of openssl cheat sheets out there already(( But as I keep using googling it again and again to find the most useful openssl commands I decided to do my own – the first version of the blog entries is already 3 years old actually. Another reason for creating the list is that I remember things better when I am writing the down.

Show contents of a certificate (( ))

openssl x509 -fingerprint -sha256 -noout -text -in

Show contents of a certificate request (CSR)

openssl req -text -noout -verify -in CSR.csr

OpenSSL HTTPS Client with SNIĀ (( ))

openssl s_client -connect -servername

Generate a CSR to send to an external CA

openssl req -new -newkey rsa:2048 -sha256 -nodes -out  -keyout  -subj "/C=US/ST=NY/L=NY/O=Roman Pertl/OU=Hostmaster/"

Generate a Self-Signed SSL Certificate

openssl req -x509 -nodes -days 365 -newkey rsa:4096 -sha256 -keyout -out -subj "/C=AT/ST=Korneuburg/L=Korneuburg/O=Pertl/OU=Hostmaster/CN=*"

Newer versions of browsers e.g. Chrome require to set the DNS alt attribute instead/additional of the CN field: ((

openssl req -x509 -nodes -days 365 -newkey rsa:4096 -sha256 -reqexts SAN -extensions SAN -config <(cat /System/Library/OpenSSL/openssl.cnf <(printf '[SAN]\nsubjectAltName=DNS:*')) -keyout -out -subj "/C=AT/ST=Korneuburg/L=Korneuburg/O=Pertl/OU=Hostmaster/CN=*"

Generate a Self-Signed CA Root Certificate

openssl req -nodes -newkey rsa:4096 -x509 -sha256 -days 3650 -keyout rootCA.key -reqexts v3_req -extensions v3_ca -out rootCA.crt -subj "/C=AT/ST=Korneuburg/L=Korneuburg/O=Pertl/OU=Hostmaster/CN=pertl CA"

Generate custom dh param file

openssl dhparam -out 4096

Cloudflare and Haproxy Lodbalancer

We are currently trying out the cloudflare service to protect one of our company service. In front of this service we are using haproxy as SSL endpoint and loadbalancer. Cloudflare adds a number of custom headers((

 _SERVER["HTTP_CF_RAY"]            17da8155355b0520-SEA
 _SERVER["HTTP_CF_VISITOR"]        {"scheme":"http"}

In order to extract the original client IP in the X_FORWARDD_FOR header, you need to use the following configuration(( in haproxy:

  acl  FROM_CLOUDFLARE src -f /etc/haproxy/cf-ips-v4
  reqidel  ^X-Forwarded-For:.* if ! LOCALHOST
  reqirep  ^CF-Connecting-IP:(.*)$ X-Forwarded-For:\1 if FROM_CLOUDFLARE
  option  forwardfor if-none

Additionally you need to have the cloudlare IPs in the file /etc/haproxy/cf-ips-v4. You can retrieve their IP ranges from:

Some additional links: