---
title: openssl Command Cheatsheet
description: "# The Linux `openssl` Command The Linux `openssl` command is a versatile utility for managing certificates, encrypting data, and implementing secure communication protocols. It provides an extensive suite of cryptographic functions, making it a cornerstone of security in Linux environments.…"
url: "https://www.relianoid.com/resources/knowledge-base/misc/openssl-command-cheatsheet/"
updated: "2025-09-10"
category: Misc
---

# openssl Command Cheatsheet

# The Linux `openssl` Command

The Linux `openssl` command is a versatile utility for managing certificates, encrypting data, and implementing secure communication protocols. It provides an extensive suite of cryptographic functions, making it a cornerstone of security in Linux environments.

OpenSSL is widely used for creating, signing, and verifying SSL/TLS certificates, managing private keys, and performing encryption/decryption tasks.

## Key Usage and Syntax of the `openssl` Command

The basic syntax of the `openssl` command is:

```
openssl  [OPTIONS]
```

- **SUBCOMMAND**: Specifies the cryptographic operation, such as `req` (certificate request), `genrsa` (generate RSA key), or `enc` (encryption).
- **OPTIONS**: Additional flags and parameters to customize the behavior of the subcommand.

## `openssl` Command Cheatsheet Table

| Command | Description |
| --- | --- |
| `openssl genrsa -out private.key 2048` | Generate a 2048-bit RSA private key |
| `openssl req -new -key private.key -out request.csr` | Create a certificate signing request (CSR) |
| `openssl x509 -req -in request.csr -signkey private.key -out certificate.crt` | Generate a self-signed certificate |
| `openssl enc -aes-256-cbc -salt -in file.txt -out file.enc` | Encrypt a file with AES-256 |
| `openssl enc -aes-256-cbc -d -in file.enc -out file.txt` | Decrypt an AES-256 encrypted file |
| `openssl s_client -connect example.com:443` | Test an SSL/TLS connection |
| `openssl dgst -sha256 -sign private.key -out signature file.txt` | Sign a file with SHA-256 |
| `openssl dgst -sha256 -verify public.pem -signature signature file.txt` | Verify a file signature |

## The `openssl req` Subcommand

### Create a Certificate Signing Request (CSR)

```
openssl req -new -key private.key -out request.csr
```

This command generates a CSR based on a private key. During execution, you will be prompted to input details such as country, organization, and common name.

### Example Output

```
Generating a 2048 bit RSA private key
......
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:California
...
```

## The `openssl x509` Subcommand

### Generate a Self-Signed Certificate

```
openssl x509 -req -in request.csr -signkey private.key -out certificate.crt
```

This command creates a self-signed certificate for testing purposes. Use a CA-signed certificate for production environments.

### Example Output

```
Signature ok
subject=/C=US/ST=California/O=MyOrg/CN=example.com
...
```

## The `openssl enc` Subcommand

### Encrypt a File

```
openssl enc -aes-256-cbc -salt -in file.txt -out file.enc
```

This command encrypts `file.txt` using AES-256 encryption, producing `file.enc`.

### Decrypt a File

```
openssl enc -aes-256-cbc -d -in file.enc -out file.txt
```

Decrypts `file.enc` back to its original form, provided the correct password is entered.

## Examples of Using the `openssl` Command

### Generate a Private Key and CSR

```
openssl genrsa -out private.key 2048
openssl req -new -key private.key -out request.csr
```

Use these commands to create a private key and CSR. Submit the CSR to a certificate authority (CA) to obtain an SSL certificate.

### Test an SSL/TLS Connection

```
openssl s_client -connect example.com:443
```

This command connects to `example.com` on port `443` to test its SSL/TLS configuration.

## Summary

The `openssl` command is an indispensable tool for security tasks in Linux. From managing certificates to encrypting data, it provides robust functionality for maintaining secure systems. Mastering `openssl` is essential for Linux administrators and anyone managing secure communications.

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