DSA_GENERATE_PARAMETERS(3ossl)

📦
version 15.1 · 3 versions
, in freebsd 15.1

💅 DSA_GENERATE_PARAMETERS 💅

okay bestie so this page lives in section 3ossl of the OpenSSL manual, and it's all about generating DSA parameters. fair warning before we even start: every single function on this page is deprecated, like fully. so consider this a history lesson with a cute vibe, not a "go do this in prod" situation. 🫶

✨ NAME ✨

DSA_generate_parameters_ex, DSA_generate_parameters — they generate DSA parameters. that's the whole job. 💅

🌸 SYNOPSIS 🌸

first things first, gotta pull in the header:

#include <openssl/dsa.h>

so listen 👀 — the following functions have been deprecated since OpenSSL 3.0, and you can hide them entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

int DSA_generate_parameters_ex(DSA *dsa, int bits,
                               const unsigned char *seed, int seed_len,
                               int *counter_ret, unsigned long *h_ret,
                               BN_GENCB *cb);

and the following functions have been deprecated since OpenSSL 0.9.8 (yes, ancient 😭), and can also be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

DSA *DSA_generate_parameters(int bits, unsigned char *seed, int seed_len,
                             int *counter_ret, unsigned long *h_ret,
                             void (*callback)(int, int, void *), void *cb_arg);

🦋 DESCRIPTION 🦋

okay so the headline: all of the functions described on this page are deprecated. no cap. instead, applications should be using EVP_PKEY_paramgen_init(3) and EVP_PKEY_keygen(3) as described in EVP_PKEY-DSA(7). that's the main character path now, these guys are retired. 👑

DSA_generate_parameters_ex() generates primes p and q and a generator g for use in the DSA and stores the result in dsa. cute little trio, they come as a set. 💜

bits is the length of the prime p to be generated. and here's the tea on lengths 🍓: for lengths under 2048 bits, the length of q is 160 bits; for lengths greater than or equal to 2048 bits, the length of q is set to 256 bits.

if seed is NULL, the primes will be generated at random. and if seed_len is less than the length of q, an error is returned. so don't try to be slick with a short seed, it will simply not work. 🙈

DSA_generate_parameters_ex() places the iteration count in *counter_ret and a counter used for finding a generator in *h_ret, unless these are NULL. (so like, pass NULL if you don't care, no pressure.)

a callback function may be used to provide feedback about the progress of the key generation. if cb is not NULL, it will be called as shown below. for information on the BN_GENCB structure and the BN_GENCB_call function discussed below, refer to BN_generate_prime(3). 📖

DSA_generate_parameters() is similar to DSA_generate_parameters_ex() but expects an old-style callback function; see BN_generate_prime(3) for info on the old-style callback. retro vibes only. 🎀

here's the whole callback timeline, in order, no skips:

  • when a candidate for q is generated, BN_GENCB_call(cb, 0, m++) is called (m is 0 for the first candidate).
  • when a candidate for q has passed a test by trial division, BN_GENCB_call(cb, 1, -1) is called. while a candidate for q is tested by Miller-Rabin primality tests, BN_GENCB_call(cb, 1, i) is called in the outer loop (once for each witness that confirms that the candidate may be prime); i is the loop counter (starting at 0).
  • when a prime q has been found, BN_GENCB_call(cb, 2, 0) and BN_GENCB_call(cb, 3, 0) are called.
  • before a candidate for p (other than the first) is generated and tested, BN_GENCB_call(cb, 0, counter) is called.
  • when a candidate for p has passed the test by trial division, BN_GENCB_call(cb, 1, -1) is called. while it is tested by the Miller-Rabin primality test, BN_GENCB_call(cb, 1, i) is called in the outer loop (once for each witness that confirms that the candidate may be prime). i is the loop counter (starting at 0).
  • when p has been found, BN_GENCB_call(cb, 2, 1) is called.
  • when the generator has been found, BN_GENCB_call(cb, 3, 1) is called.

like, that's a lot of callbacks but they're all listed, we don't gatekeep here. 💖

⭐ RETURN VALUES ⭐

DSA_generate_parameters_ex() returns a 1 on success, or 0 otherwise. the error codes can be obtained by ERR_get_error(3).

DSA_generate_parameters() returns a pointer to the DSA structure or NULL if the parameter generation fails. simple as that. 🎀

💀 BUGS 💀

seed lengths greater than 20 are not supported. that's it, that's the bug note. lowkey annoying but there it is. 🙃

🌈 SEE ALSO 🌈

go read these besties, they're all linked:

DSA_new(3), ERR_get_error(3), RAND_bytes(3), DSA_free(3), BN_generate_prime(3)

🧚 HISTORY 🧚

  • DSA_generate_parameters_ex() was deprecated in OpenSSL 3.0.
  • DSA_generate_parameters() was deprecated in OpenSSL 0.9.8; use DSA_generate_parameters_ex() instead.

Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

and that's the page, bestie! 🫶 this one's from OpenSSL version 3.5.6, dated 2026-04-07, and it's DSA_GENERATE_PARAMETERS(3ossl) — go forth and, like, please use EVP_PKEY_paramgen_init(3) instead. slay! 💖✨

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