How to debug network issues in Unix — “openssl”

Photo by Sai Kiran Anagani on Unsplash

In my day-by-day job, I started to use lots of BASH commands to debug network issues, and I did never not many of them. This is why I decided to write here all those commands and how do I use usually.

This is a series. Here the table of contents:

1. dig
2. ping
3. whois
4. openssl (this story)
5. nslookup
6. traceroute and mtr
7. iptables
8. network configuration and statistics
9. tcpdump

Restarting with my personal network debug toolkit, today I will describe openssl.

As described by its web site, OpenSSL is a robust, commercial-grade, and full-featured toolkit for the Transport Layer Security (TLS) and Secure Sockets Layer (SSL) protocols, but also a general-purpose cryptography library.

With openssl it is possible to verify if a TLS/SSL certificate is still valid or not for a specific website, or retrieve the certificates, or verify ciphers, or verify which TLS version is supported.

Test SSL certificate of particular URL

echo | openssl s_client -connect yoururl.com:443 -showcerts

Check Certificate Expiration Date of SSL URL

echo | openssl s_client -connect yoururl.com:443 -showcerts echo | openssl s_client -connect secureurl.com:443 2>/dev/null | openssl x509 -noout -startdate -enddate

Check if SSL V2 or V3 is accepted on URL

Depending on openssl version you are using, you could test if various SSL or TLS versions are enable for an URL.
To check SSL v2

echo | openssl s_client -connect secureurl.com:443 -ssl2

To Check SSL v3

echo | openssl s_client -connect secureurl.com:443 -ssl3

To Check TLS 1.0

echo | openssl s_client -connect secureurl.com:443 -tls1

To Check TLS 1.1

echo | openssl s_client -connect secureurl.com:443 -tls1_1

To Check TLS 1.2

echo | openssl s_client -connect secureurl.com:443 -tls1_2

Further details on https://geekflare.com/openssl-commands-certificates or on https://gist.github.com/shpatserman/3cfcb59e40cf4381a5cec79b700ad98c.

Originally published at https://gabriele-decapoa.github.io.