How to use the command `openssl genrsa` (with examples)
This command is used to generate RSA private keys. It is a part of the OpenSSL toolkit, which is a robust, full-featured open-source toolkit that implements the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols. The openssl genrsa command allows users to generate RSA private keys of various sizes and with different encryption methods.
Use case 1: Generate an RSA private key of 2048 bits to stdout
Code:
openssl genrsa
Motivation: In this use case, the command openssl genrsa is used without any additional arguments, generating an RSA private key of 2048 bits and printing it to the standard output (stdout). This can be useful when you need to obtain the RSA private key for further use in a script or other operations.
Explanation:
genrsa: This subcommand generates an RSA private key.- No additional arguments or options provided.
Example output:
-----BEGIN RSA PRIVATE KEY-----
MIIEowIBAAKCAQEApEGKcI1F3bToYNLVNonjvcY0RJQGPxYMHowxPSX6rzpScsDy
QmwMkaqWw3qgVydk5a5z5eiaW8Jvv8Ly4TFIkxip/+qY4FUHpOituz+mYe1PsnBy
/ng96XsfR5bYwY8fPVeT3LrVGRtRakhOyCh/OATzamXQ19Jb31Lq+Z7T5fwXvZBR
...
gjGATWDFDChvewMici45nNU79ChfnSZLi/0x90nNZJKd4bGCYU3uPEXiLQRcYhrh
F5bezJ3b6EsXzSma6wsgx+VeUr/IT7P90oaunU0vQDsTcN570yYO0g==
-----END RSA PRIVATE KEY-----
Use case 2: Save an RSA private key of an arbitrary number of bits to the output file
Code:
openssl genrsa -out output_file.key 1234
Motivation: In this use case, the command openssl genrsa is used with the -out option to save the generated RSA private key to a file named output_file.key. The specified number of bits for the key is arbitrary and can be adjusted as needed. This is helpful when you want to generate an RSA private key and store it in a separate file for future use.
Explanation:
genrsa: This subcommand generates an RSA private key.-out output_file.key: This option specifies the output file name for the RSA private key.1234: This argument defines the number of bits for the RSA private key.
Example output:
Generating RSA private key, 1234 bit long modulus
.......++++++++......++++++++
e is 65537 (0x010001)
The RSA private key will be saved to a file named output_file.key in the current directory.
Use case 3: Generate an RSA private key and encrypt it with AES256 (you will be prompted for a passphrase)
Code:
openssl genrsa -aes256
Motivation: In this use case, the command openssl genrsa is used with the -aes256 option to generate an RSA private key and encrypt it using the AES256 encryption algorithm. This adds an extra layer of security to the private key by requiring a passphrase for decryption. By using this option, sensitive RSA private keys can be protected from unauthorized access.
Explanation:
genrsa: This subcommand generates an RSA private key.-aes256: This option tells OpenSSL to encrypt the generated RSA private key using AES256 encryption.
Example output:
Generating RSA private key, 2048 bit long modulus
..............+++
.............................................................................................................................................................................................+++
e is 65537 (0x010001)
Enter pass phrase for <stdin>:
Verifying - Enter pass phrase for <stdin>:
After executing the command, you will be prompted to enter a passphrase for the encryption. The RSA private key will then be encrypted with AES256 and saved for future use.
Conclusion:
The openssl genrsa command is a versatile tool for generating RSA private keys in various scenarios. It allows users to generate keys of specific sizes, save them to files, and encrypt them for increased security. By understanding the different use cases and options available for this command, users can effectively generate and manage RSA private keys for their encryption needs.
