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openssl

securityLinux/Unix/Windows

The openssl command is one of the most frequently used commands in Linux/Unix-like operating systems. openssl Cryptography and SSL/TLS toolkit

See Examples View Syntax

Quick Reference

Command Name:

openssl

Category:

security

Platform:

Linux/Unix/Windows

Basic Usage:

openssl [options] [arguments]

Common Use Cases

Syntax

openssl command [command_options] [command_arguments]

Options

Standard Option	Description
`-help`	Display help for a command
`-h`	Same as -help for most commands
`-v`	Verbose mode
`-in file`	Input file
`-out file`	Output file
`-engine id`	Use the specified engine

Common OpenSSL Commands:

Command	Description
`genrsa`	Generate RSA private key
`rsa`	Process RSA keys
`req`	PKCS#10 certificate request and certificate generating utility
`x509`	X.509 certificate data management
`ca`	Certificate Authority (CA) management
`verify`	Certificate verification
`pkcs12`	PKCS#12 data management
`dgst`	Compute message digests (hashes)
`enc`	Encoding with ciphers
`rand`	Generate random bytes
`s_client`	Implement a generic SSL/TLS client
`s_server`	Implement a generic SSL/TLS server
`speed`	Test the speed of cryptographic algorithms
`version`	Display OpenSSL version information
`list`	List algorithms, ciphers, commands, etc.

Common Options for 'req' Command:

Option	Description
`-new`	Generate a new certificate request
`-x509`	Output a self-signed certificate instead of a certificate request
`-days n`	Number of days the certificate is valid for
`-key file`	Use the private key in file
`-subj arg`	Set certificate subject (e.g., '/CN=example.com')

Examples

How to Use These Examples

The examples below show common ways to use the openssl command. Try them in your terminal to see the results. You can copy any example by clicking on the code block.

# Basic Examples Basic

openssl version

Display OpenSSL version information.

openssl list -commands

List all available OpenSSL commands.

# Advanced Examples Advanced

# Generate a 2048-bit RSA private key openssl genrsa -out private.key 2048 # Create a self-signed certificate openssl req -x509 -new -key private.key -out cert.crt -days 365 # View certificate information openssl x509 -in cert.crt -text -noout # Verify certificate against CA openssl verify -CAfile ca.crt cert.crt # Create a CSR (Certificate Signing Request) openssl req -new -key private.key -out request.csr # Generate a random password openssl rand -base64 12 # Calculate file hash openssl dgst -sha256 file.txt # Encrypt a file with AES-256 openssl enc -aes-256-cbc -salt -in file.txt -out file.enc # Decrypt a file openssl enc -aes-256-cbc -d -in file.enc -out file.txt # Test SSL/TLS connection to a server openssl s_client -connect example.com:443

Try It Yourself

Practice makes perfect! The best way to learn is by trying these examples on your own system with real files.

Understanding Syntax

Pay attention to the syntax coloring: commands, options, and file paths are highlighted differently.

Notes

OpenSSL is a robust, full-featured open-source toolkit that implements the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols, as well as a general-purpose cryptography library. It's widely used across the internet to secure communications, establish identity verification, and ensure data integrity and privacy. As one of the most important security tools in the Linux ecosystem, OpenSSL provides a comprehensive suite of cryptographic functions, including encryption, decryption, digital signatures, certificate management, and much more. It's the foundation for securing web servers, email systems, VPNs, and countless other applications that require secure communications. Key features of the OpenSSL command: 1. Certificate Management: OpenSSL provides a complete suite of tools for creating, managing, and verifying X.509 certificates, certificate signing requests (CSRs), and certificate authorities (CAs). 2. Cryptographic Operations: It supports a wide range of cryptographic algorithms for encryption, decryption, digital signatures, and message authentication. 3. SSL/TLS Protocol Support: OpenSSL allows testing and debugging of SSL/TLS connections, acting as both client and server to verify secure communication channels. 4. Key Generation and Management: The toolkit facilitates the creation and manipulation of various types of cryptographic keys, including RSA, DSA, and elliptic curve. 5. Hashing and Message Digests: OpenSSL provides tools for generating message digests and hashes using algorithms like SHA-256, SHA-512, and others. 6. Random Number Generation: It includes secure random number generation capabilities, essential for cryptographic operations. 7. Extensibility: The framework supports engines and plugins, allowing for hardware acceleration and custom cryptographic implementations. Common use cases for OpenSSL include: - Setting up HTTPS for web servers by generating and managing SSL/TLS certificates - Creating and managing public key infrastructure (PKI) - Encrypting sensitive files and communications - Testing the security configuration of remote servers - Generating secure passwords and random data - Verifying digital signatures and certificate chains - Implementing secure communication channels in custom applications - Converting between different certificate and key formats While extremely powerful, OpenSSL has a notably complex command-line interface with numerous subcommands, each with its own set of options. This complexity reflects the multifaceted nature of cryptography and secure communications but can make it challenging for newcomers. OpenSSL's importance to internet security cannot be overstated; it's used by approximately two-thirds of all web servers worldwide. However, this ubiquity also means that security vulnerabilities in OpenSSL can have far-reaching implications, as demonstrated by the Heartbleed bug discovered in 2014, which affected millions of servers globally. Despite such challenges, OpenSSL continues to evolve with regular security updates and feature improvements, maintaining its position as an essential tool for system administrators, security professionals, and developers working on secure systems.

Related Commands

These commands are frequently used alongside openssl or serve similar purposes:

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Use Cases

Learn By Doing

The best way to learn Linux commands is by practicing. Try out these examples in your terminal to build muscle memory and understand how the openssl command works in different scenarios.

See Examples Try Lab Exercises

$ openssl

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