By apipark — 02 Jul 2025

Unlock the Mystery: How to View SSL Certificates with OpenSSL s_client (-showcert)!

openssl s_client not showing cert with -showcert

In today's digital age, SSL certificates play a crucial role in securing online communications. As a system administrator or security professional, understanding how to view SSL certificates is essential. One of the most popular tools for this task is OpenSSL, a robust, cross-platform tool for managing SSL and TLS certificates. This article delves into the nuances of using the s_client command with the -showcerts option in OpenSSL to view SSL certificates.

Introduction to OpenSSL and SSL Certificates

Before we dive into the specifics of viewing SSL certificates, let's establish a basic understanding of OpenSSL and SSL certificates.

OpenSSL is an open-source software library that provides cryptographic functions and supports SSL and TLS protocols. It is widely used for secure communications over the internet.

SSL Certificates are digital certificates that serve as a form of identification for websites. They are issued by Certification Authorities (CAs) and used to authenticate the sender of data and ensure that the data is transmitted securely.

Understanding the s_client Command

The s_client command in OpenSSL is a general-purpose SSL/TLS client that can be used to connect to an SSL/TLS server. It is a versatile tool for testing SSL/TLS connections and examining the SSL/TLS handshake process.

Usage of s_client

The basic usage of the s_client command is as follows:

openssl s_client -connect [host]:[port]

This command connects to the specified host and port using SSL/TLS. However, to view SSL certificates, we need to add the -showcerts option.

The -showcerts Option

The -showcerts option in the s_client command tells OpenSSL to print the entire chain of certificates for the peer. This is useful for verifying the certificate chain and checking the validity of the certificate.

How to View SSL Certificates with -showcerts

To view SSL certificates using the s_client command with the -showcerts option, follow these steps:

Open a terminal or command prompt.
Run the following command, replacing [host] with the domain name of the website and [port] with the port number:

openssl s_client -connect [host]:[port] -showcerts

The output will display the SSL certificate chain for the specified host.

Example Output

Here is an example of what the output might look like when you use the s_client command with the -showcerts option:

...
Certificate chain
 0 s:/C=US/ST=California/L=San Francisco/O=Example Inc/CN=www.example.com
   i:/C=US/ST=California/L=San Francisco/O=Example Inc/CN=www.example.com
...

In this output, the first line represents the server's certificate, while the second line represents the Intermediate Certificate issued by the Certification Authority.

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Interpreting the Certificate Chain

The certificate chain is a sequence of certificates that link the server's certificate to the root certificate of the Certification Authority. It is crucial to ensure that the chain is complete and valid.

The first line in the output (0 s:/...) represents the server's certificate.
The second line (i:/...) represents the Intermediate Certificate.
The subsequent lines represent the certificate chain, with each line prefixed by i:.

Troubleshooting Common Issues

When using the s_client command to view SSL certificates, you may encounter some common issues. Here are some tips for troubleshooting:

Connection Refused: Ensure that the host and port are correct and that the server is running.
Certificate Error: Verify that the certificate chain is complete and valid. If the certificate is self-signed, it may not be trusted by your system.
Timeout Error: Check your network connection and ensure that the server is responding.

Conclusion

Viewing SSL certificates using the s_client command with the -showcerts option in OpenSSL is a valuable skill for system administrators and security professionals. By understanding the certificate chain and its significance, you can ensure the security and integrity of your online communications.

Table: OpenSSL s_client Command Options

Option	Description
`-connect`	Specifies the host and port to connect to.
`-showcerts`	Prints the entire chain of certificates for the peer.
`-servername`	Specifies the server name to use for Server Name Indication (SNI).
`-servername`	Specifies the server name to use for Server Name Indication (SNI).
`-verify`	Verifies the certificate chain and checks the certificate's validity.
`-CAfile`	Specifies a file containing the trusted root certificates.
`-no_verify`	Disables certificate verification.

Frequently Asked Questions (FAQ)

Q1: Why do I need to view SSL certificates? A1: Viewing SSL certificates helps you verify the authenticity and integrity of the website you are connecting to, ensuring that your data is transmitted securely.

Q2: How can I ensure that the SSL certificate is valid? A2: Check the certificate chain to ensure it is complete and valid. Verify that the certificate is issued by a trusted Certification Authority.

Q3: What should I do if the SSL certificate is self-signed? A3: Self-signed certificates are not trusted by default. You can either add the certificate to your list of trusted certificates or use a certificate issued by a trusted Certification Authority.

Q4: How do I view the SSL certificate for a specific website? A4: Use the openssl s_client -connect [host]:[port] -showcerts command, replacing [host] with the domain name of the website and [port] with the port number.

Q5: Can I use the s_client command to test the security of an SSL/TLS connection? A5: Yes, the s_client command can be used to test the security of an SSL/TLS connection by examining the certificate chain and checking for any vulnerabilities or weaknesses in the handshake process.

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