This article will illustrate various use cases of the openssl genpkey command, which is used to generate asymmetric key pairs. The openssl genpkey command is part of the OpenSSL toolkit and provides a flexible way to generate keys using different algorithms and parameters.

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: Generating an RSA private key with a key size of 2048 bits is considered secure for most general-purpose applications. This use case will generate a new RSA private key and save it to the file filename.key.

Explanation:

• genpkey: The genpkey subcommand is used to generate an asymmetric key pair.
• -algorithm rsa: Specifies the algorithm to be used for key generation, in this case, RSA.
• -pkeyopt rsa_keygen_bits:2048: Sets the key size to 2048 bits using the rsa_keygen_bits option.
• -out filename.key: Specifies the output file where the generated private key will be saved.

Example Output:

-----BEGIN RSA PRIVATE KEY-----
MIIEogIBAAKCAQEAr8FjwCfWJ87CUmo2NUUFj5KmSkQac8QWTloVLVOqqwQ8b3dh
...
...
-----END RSA PRIVATE KEY-----

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

Code:

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

Motivation: Elliptic curve cryptography is becoming more popular due to its smaller key sizes and stronger security compared to traditional RSA. This use case generates a new EC private key using the prime256v1 curve, also known as secp256r1 or P-256.

Explanation:

• genpkey: The genpkey subcommand is used to generate an asymmetric key pair.
• -algorithm EC: Specifies the algorithm to be used for key generation, in this case, elliptic curve.
• -pkeyopt ec_paramgen_curve:prime256v1: Sets the curve to prime256v1 using the ec_paramgen_curve option.
• -out filename.key: Specifies the output file where the generated private key will be saved.

Example Output:

-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIOYmgkkoYD7BdGlDKERbVUINhbERiC96xDS/ttxiUZEGoAoGCCqGSM49
...
...
-----END EC PRIVATE KEY-----

Use case 3: Generate an ED25519 elliptic curve private key

Code:

openssl genpkey -algorithm ED25519 -out filename.key

Motivation: ED25519 is an elliptic curve digital signature algorithm that provides strong security and high performance. This use case generates a new ED25519 private key, which is suitable for various cryptographic operations, including digital signatures.

Explanation:

• genpkey: The genpkey subcommand is used to generate an asymmetric key pair.
• -algorithm ED25519: Specifies the algorithm to be used for key generation, in this case, ED25519.
• -out filename.key: Specifies the output file where the generated private key will be saved.

Example Output:

-----BEGIN PRIVATE KEY-----
MC4CAQAwBQYDK2VwBCIEIPNyo83J/4gg6cB3hFkgfXUpW/3eBl9Mr2A7EOt8jdz9
...
...
-----END PRIVATE KEY-----

Conclusion

The openssl genpkey command is a powerful tool for generating asymmetric key pairs. It offers flexibility to choose different algorithms and parameters based on the specific requirements of the application. The examples provided in this article demonstrate how to generate RSA keys, elliptic curve keys using the prime256v1 curve, and ED25519 keys. By understanding the use cases and options of the openssl genpkey command, users can generate secure and appropriate keys for their cryptographic needs.