How to use the command 'openssl' (with examples)

The OpenSSL command-line tool is a powerful utility for working with cryptographic operations. It provides a wide range of functionalities related to SSL/TLS protocols, cryptography, and certificates. This article will illustrate some common use cases of the ‘openssl’ command.

Use case 1: Print a list of available subcommands

Code:

openssl help

Motivation:

When first starting with OpenSSL, it can be overwhelming to remember all the available subcommands and options. By using the ‘openssl help’ command, you can quickly retrieve a list of available subcommands. This is especially helpful for beginners or when you need a refresher.

Explanation:

The ‘openssl help’ command is used to display a list of available OpenSSL subcommands. It does not accept any arguments. Upon execution, it will print a list of subcommands along with a brief description for each subcommand.

Example output:

Standard commands
asn1parse         ca                ciphers           cms               crl
crl2pkcs7         dgst              dh                dhparam           dsa
dsaparam          ec                ecparam           enc               engine
errstr            gendsa            genpkey           genrsa            help
list              nseq              ocsp              passwd            pkcs12
pkcs7             pkcs8             pkey              pkeyparam         pkeyutl
prime             rand              rehash            req               rsa
rsautl            s_client          s_server          s_time            sess_id
smime             speed             spkac             srp               storeutl
ts                verify            version           x509

Use case 2: Print options for a specific subcommand

Code:

openssl help x509

Motivation:

When you are working on a specific task using the OpenSSL command, it can be helpful to display the available options specifically for that subcommand. The ‘openssl help’ command can be used along with the desired subcommand to get detailed information about its options and usage.

Explanation:

The ‘openssl help’ command is used to display the usage documentation for a specific subcommand. In this example, it is used to get information about the ‘x509’ subcommand. By specifying ‘x509’ after ‘openssl help’, it will display the usage information, available options, and examples specific to the ‘x509’ subcommand.

Example output:

openssl x509 [-inform DER | PEM | NET] [-outform DER | PEM | NET]
             [-text] [-noout] [-pubkey] [-in file] [-out file]
             [-serial] [-signkey file] [-req] [-CAcreateserial]
             [-CAserial file] [-CA file] [-CAkey file] [-CAform PEM | DER]
             [-CAkeyform PEM | DER] [-CAspki] [-CAprefix path] [-CAfile file]
             [-caname arg] [-setalias name] [-days n] [-enddate date]
             [-engine id] [-extensions section] [-extfile file]
             [-includeflags] [-issuer_checks] [-subject_checks]
             [-purpose purpose] [-trusted_first] [-allow_proxy_certificates]
             [-proxy_certinfo] [-trustout] [-ignore_critical] [-issuer_checks]...

Use case 3: Print the version of OpenSSL

Code:

openssl version

Motivation:

Knowing the version of OpenSSL you are using can be crucial when debugging issues or ensuring compatibility with other tools or libraries. The ‘openssl version’ command allows you to quickly retrieve the installed OpenSSL version.

Explanation:

The ‘openssl version’ command prints the OpenSSL version number installed on your system. It does not require any arguments and simply outputs the version information.

Example output:

OpenSSL 1.1.1k  25 Mar 2021

Conclusion:

The ‘openssl’ command is a versatile tool for cryptography-related operations. In this article, we covered three common use cases of the command. We learned how to print a list of available subcommands, how to get detailed information about options for a specific subcommand, and how to retrieve the OpenSSL version. These examples will help you get started with using the ‘openssl’ command effectively.