dsaparam.1s

dsaparam [-in filename] [-out filename] [-text] [-noout] [-inform format] [-outform format] [-C] [-genkey] [-rand file(s)] [-new] [num_bits]

-in filename
    Specifies the input file for DSA parameters. If not specified, standard input is used.

-out filename
    Specifies the output file for DSA parameters. If not specified, standard output is used.

-text
    Prints the DSA parameters in a human-readable text format.

-noout
    Prevents the output of the encoded version of the parameters. Useful when only printing text or verifying.

-inform format
    Specifies the input format of the parameters. Valid formats are PEM (default) and DER.

-outform format
    Specifies the output format of the parameters. Valid formats are PEM (default) and DER.

-C
    Outputs the DSA parameters in C source code format, suitable for embedding in applications.

-genkey
    Generates a DSA private key using the specified parameters and outputs it.

-rand file(s)
    Specifies one or more files to seed the random number generator, enhancing security.

-new
    Generates a new set of DSA parameters. This option requires specifying the bit length.

num_bits
    When using the -new option, this argument specifies the desired number of bits for the prime p parameter (e.g., 1024, 2048, 3072). Larger values provide stronger security but take longer to generate.

The dsaparam command is a utility within the OpenSSL toolkit used for generating, managing, and verifying DSA (Digital Signature Algorithm) parameters.

DSA requires a set of shared global parameters (p, q, g) that are fundamental for creating and verifying DSA signatures. These parameters ensure the cryptographic strength and interoperability of DSA keys within a system. dsaparam can generate new sets of these parameters, print existing ones in various formats (e.g., PEM, DER), or verify their correctness.

It is commonly used as a foundational step before generating DSA private and public keys, as the parameters define the mathematical group within which DSA operations occur.

DSA, while still supported, is less commonly used for new cryptographic deployments compared to modern alternatives like RSA or ECC.

Generating large DSA parameters can be computationally intensive and time-consuming, requiring significant processing power. The security of generated parameters relies heavily on the quality and entropy of the random number generator used. Reusing well-known or compromised parameters can severely compromise the security of any associated DSA keys.

The security of DSA signatures depends critically on the quality and strength of the generated parameters. Using sufficiently large parameters (e.g., 2048 bits or more as recommended by NIST) and a cryptographically secure random number generator is paramount to prevent various cryptographic attacks.

A common workflow involves first generating DSA parameters using dsaparam -new num_bits -out parameters.pem. Subsequently, a DSA private key can be generated using these parameters (e.g., with openssl dsa -in parameters.pem -genkey -out privatekey.pem or via dsaparam -genkey). These parameters are then often distributed or used internally to ensure interoperability among parties using DSA keys.

The DSA (Digital Signature Algorithm) was first specified by the National Institute of Standards and Technology (NIST) in FIPS 186 in 1991. The dsaparam command has been a fundamental part of the OpenSSL cryptographic toolkit since its early versions, providing the necessary tools to generate and manage the global parameters required for DSA key generation and signature operations. Its usage reflects the continued importance of DSA in various cryptographic standards and applications.

openssl(1ssl), dsa(1ssl), genrsa(1ssl), ecparam(1ssl)