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

OpenSSL is a robust, full-featured open-source toolkit implementing the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols. The command openssl genpkey is utilized for generating asymmetric key pairs, which are essential in ensuring security in cryptographic operations, such as encryption and digital signatures. This command provides cryptographic strength by generating private keys that can be used in conjunction with public keys to secure communications over networks. In this article, we will explore various use cases of this command, demonstrating how to generate different types of private keys.

Use case 1: Generate an RSA private key of 2048 bits

Code:

openssl genpkey -algorithm rsa -pkeyopt rsa_keygen_bits:2048 -out filename.key

Motivation for using the example:

RSA (Rivest-Shamir-Adleman) is one of the most widely-used encryption and authentication algorithms, making the generation of RSA keys a fundamental task in many cryptographic operations. A 2048-bit RSA key is generally considered secure for most applications. It provides a balance between security and performance, making it a common choice for securing data, encrypting files, and establishing secure connections over the internet.

Explanation for every argument in the command:

• openssl genpkey: This is the OpenSSL command used to generate private keys of various algorithms.
• -algorithm rsa: This option specifies that the RSA algorithm will be used to generate the key.
• -pkeyopt rsa_keygen_bits:2048: This sets the key length to 2048 bits, which is a common standard for RSA keys.
• -out filename.key: Indicates the file where the generated private key will be saved.

Example output:

Upon successful execution, the command outputs a file named filename.key containing the RSA private key. You can view the formatted output with the command cat filename.key.

Use case 2: Generate an elliptic curve private key using the curve prime256v1

Code:

openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:prime256v1 -out filename.key

Motivation for using the example:

Elliptic Curve Cryptography (ECC) offers a higher degree of security with smaller keys compared to non-ECC cryptography like RSA. The prime256v1 curve, also known as NIST P-256, offers a good level of security and is widely adopted for cryptographic protocols including TLS. This curve generally provides similar security to a 3072-bit RSA key, making it efficient for performance-sensitive applications.

Explanation for every argument in the command:

• openssl genpkey: This initiates the OpenSSL tool to generate private keys.
• -algorithm EC: Specifies the use of Elliptic Curve Cryptography for key generation.
• -pkeyopt ec_paramgen_curve:prime256v1: Sets the elliptic curve to prime256v1, ensuring that the key generated will conform to this well-known curve.
• -out filename.key: Determines the output file where the private key will be stored.

Example output:

Executing this command will produce a file called filename.key containing the elliptic curve private key. You can inspect the file with cat filename.key.

Use case 3: Generate an ED25519 elliptic curve private key

Code:

openssl genpkey -algorithm ED25519 -out filename.key

Motivation for using the example:

ED25519 is known for being fast and secure, designed for use in digital signature along with achieving strong security with smaller key sizes. It is particularly valued in scenarios where speed is of the essence and computational resources are limited. Its resistance to certain types of cryptographic attacks makes it popular for modern cryptographic applications.

Explanation for every argument in the command:

• openssl genpkey: This command triggers OpenSSL to start key generation.
• -algorithm ED25519: Specifies the generation of a private key using the ED25519 algorithm, which is known for its high-performance digital signature capabilities.
• -out filename.key: Identifies the destination file for the new private key.

Example output:

Upon execution, a file named filename.key is generated, containing the ED25519 key. To view its contents, you can use the cat filename.key command.

Conclusion:

The openssl genpkey command is a versatile and powerful tool for generating different types of asymmetric keys necessary for securing data and communications effectively. As demonstrated in the above examples, OpenSSL provides flexibility for choosing cryptographic algorithms that best fit specific security needs, whether it is classic RSA, efficient ECC, or high-performance ED25519. Understanding and utilizing these commands is crucial for developers and security professionals aiming to implement robust cryptographic solutions.