openssl command in Linux

OpenSSL is a versatile command-line tool in Linux for managing SSL/TLS protocols and certificates. It enables various cryptographic functions such as generating keys, creating CSRs, encrypting files, creating signatures, and testing SSL connections effectively.

openssl Syntax:

openssl [options] [command] [command_options] [parameters]

Linux openssl Options:

Option	Description
-help	Display a list of all available options
-version	Display the openssl version
-rand	Use specified file or files as a source of random data
-engine	Specify an engine (by name) for use
-config	Use the specified configuration file
-c	Output the certificate
-subject	Output the subject
-CAfile	Verify certificates against the list of trusted CA certificates in the file
-pubin	Expect a public key in input file
-pubout	Output a public key
-text	Output the key or certificate in text form

openssl Parameters:

Parameter	Description
input_file	Input file for the command
output_file	Output file for the command
certificate	Certificate file for operations
key_file	Key file for operations
message_digest	Message digest algorithm to use
signature_file	Signature file for verification

Caution

Exercise caution when using the openssl command, as it involves handling cryptographic operations which can result in data loss or security vulnerabilities if not used correctly.

How to use openssl command:

Generate a new RSA private key

openssl genrsa -out private.key 2048

Generates a new 2048-bit RSA private key and saves it to a file named “private.key”.

Generate a new self-signed certificate

openssl req -new -x509 -key private.key -out certificate.crt -days 365

Creates a self-signed certificate using the private key “private.key” that is valid for 365 days.

Encrypt a file using AES

openssl enc -aes-256-cbc -in file.txt -out encrypted.txt

Encrypts the contents of “file.txt” using AES-256-CBC and saves the encrypted data to “encrypted.txt”.

Decrypt a file using AES

openssl enc -d -aes-256-cbc -in encrypted.txt -out decrypted.txt

Decrypts the contents of “encrypted.txt” using AES-256-CBC and saves the decrypted data to “decrypted.txt”.

Create a SHA-256 hash of a file

openssl dgst -sha256 file.txt

Generates a SHA-256 hash of the file “file.txt”.

Verify the integrity of a file using a signature

openssl dgst -sha256 -verify public.pem -signature signature.sign file.txt

Verifies the integrity of “file.txt” by using a signature file “signature.sign” and a public key from “public.pem”.

Generate a CSR (Certificate Signing Request)

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

Creates a Certificate Signing Request (CSR) using the private key “private.key” and saves it to “csr.csr”.

Convert a PEM file to DER format

openssl x509 -outform der -in certificate.pem -out certificate.der

Converts a certificate file “certificate.pem” from PEM format to DER format and saves it as “certificate.der”.

Tip

When using the openssl command in Linux, make sure to familiarize yourself with the various options and parameters available for different operations. Reading the documentation or seeking help online can greatly assist in effectively utilizing the power of openssl for encryption, decryption, and various other cryptographic tasks.

How do I use openssl in bash?

To use the openssl command in Linux, execute the following command:

openssl --option <value>

What is the command to generate a new RSA key pair using openssl in Linux?

To generate a new RSA key pair using openssl in Linux, use the following command:

openssl genrsa -out private.pem 2048

How can I create a self-signed SSL certificate with openssl in Linux?

To create a self-signed SSL certificate using openssl in Linux, run the following command:

openssl req -newkey rsa:2048 -nodes -keyout key.pem -x509 -days 365 -out certificate.pem

How do I encrypt a file with a password using openssl in Linux?

To encrypt a file with a password using openssl in Linux, use the following command:

openssl enc -aes-256-cbc -salt -in input.txt -out output.enc

What is the command to decrypt a file that was encrypted with openssl in Linux?

To decrypt a file that was encrypted using openssl in Linux, you can use the following command:

openssl enc -d -aes-256-cbc -in output.enc -out decrypted.txt

How can I convert a certificate from PEM to DER format using openssl in Linux?

To convert a certificate from PEM to DER format using openssl in Linux, execute the following command:

openssl x509 -outform der -in certificate.pem -out certificate.der

How do I extract the public key from a certificate using openssl in Linux?

To extract the public key from a certificate using openssl in Linux, run the following command:

openssl x509 -in certificate.pem -pubkey -noout -out public_key.pem

What command can I use to create a SHA-256 hash of a file using openssl in Linux?

To create a SHA-256 hash of a file using openssl in Linux, use the following command:

openssl dgst -sha256 filename.txt

How can I verify an RSA signature using openssl in Linux?

To verify an RSA signature using openssl in Linux, you can run the following command:

openssl rsautl -verify -in signature.bin -inkey public_key.pem -pubin

Applications of the openssl command

• Creating and managing SSL/TLS certificates
• Encrypting and decrypting files
• Generating cryptographic keys
• Creating secure connections for network communication
• Testing SSL/TLS security of servers
• Creating and verifying digital signatures
• Creating and managing CSR (Certificate Signing Request)
• Converting certificate formats