EVP_PKEY-DSA(7SSL)

📦
version 4.0.3 · 13 versions
, in ubuntu stonking

💅 NAME 💅

EVP_PKEY-DSA, EVP_KEYMGMT-DSA — bestie, this is the DSA keytype and algorithm support for EVP_PKEY, and yes we're gonna get into it. This page lives in the OpenSSL manual set as EVP_PKEY-DSA(7SSL), so if you were looking for the DSA glow-up in openssl, you're in the right place. 🦋

✨ DESCRIPTION ✨

okay so here's the tea. For DSA, the FIPS 186-4 standard says that the values used for FFC parameter generation are also required for parameter validation. Which means the optional FFC domain parameter values for seed, pcounter and gindex may need to be stored, purely so validation can happen later. And here's the messy part: for DSA these fields are not stored in the ASN1 data, so if you need validation, you have to stash them externally yourself. no cap. 🙈

Also, as part of FIPS 140-3, DSA is not longer FIPS approved for key generation and signature validation — but it's still allowed for signature verification. Like, it's not cancelled, it's just demoted. 💀

🌸 DSA parameters 🌸

The DSA key type supports the FFC parameters (peep "FFC parameters" in EVP_PKEY-FFC(7)).

It also supports these, babes:

  • "sign-check" (OSSL_PKEY_PARAM_FIPS_SIGN_CHECK) — takes <integer>
  • "fips-indicator" (OSSL_PKEY_PARAM_FIPS_APPROVED_INDICATOR) — takes <integer>

For more on those, go read "Common Information Parameters" in provider-keymgmt(7). 📖

🎀 DSA key generation parameters 🎀

The DSA key type supports the FFC key generation parameters (see "FFC key generation parameters" in EVP_PKEY-FFC(7)).

But there are restrictions on the "pbits" field, and you must respect them:

  • For "fips186_4" this must be either 2048 or 3072.
  • For "fips186_2" this must be 1024.
  • For "group" this can be any one of 2048, 3072, 4096, 6144 or 8192.
pick the wrong number and it's giving "not approved", so choose wisely bestie. 💅

👑 DSA key validation 👑

For DSA keys, EVP_PKEY_param_check(3) behaves in the following way: the OpenSSL FIPS provider conforms to the rules within the FIPS186-4 standard for FFC parameter validation. For backwards compatibility, the OpenSSL default provider uses a much simpler check (scroll down, it's below) for parameter validation — unless the seed parameter is set.

For DSA keys, EVP_PKEY_param_check_quick(3) behaves in the following way: a simple check of L and N and partial g is performed. The default provider also supports validation of legacy "fips186_2" keys.

For DSA keys, EVP_PKEY_public_check(3), EVP_PKEY_private_check(3) and EVP_PKEY_pairwise_check(3): the OpenSSL default and FIPS providers conform to the rules within SP800-56Ar3 for public, private and pairwise tests respectively.

🔥 EXAMPLES 🔥

An EVP_PKEY context can be obtained by calling:

EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_from_name(NULL, "DSA", NULL);

The DSA domain parameters can be generated by calling:

unsigned int pbits = 2048;
unsigned int qbits = 256;
int gindex = 1;
OSSL_PARAM params[5];
EVP_PKEY *param_key = NULL;
EVP_PKEY_CTX *pctx = NULL;

pctx = EVP_PKEY_CTX_new_from_name(NULL, "DSA", NULL);
EVP_PKEY_paramgen_init(pctx);

params[0] = OSSL_PARAM_construct_uint("pbits", &pbits);
params[1] = OSSL_PARAM_construct_uint("qbits", &qbits);
params[2] = OSSL_PARAM_construct_int("gindex", &gindex);
params[3] = OSSL_PARAM_construct_utf8_string("digest", "SHA384", 0);
params[4] = OSSL_PARAM_construct_end();
EVP_PKEY_CTX_set_params(pctx, params);

EVP_PKEY_generate(pctx, &param_key);
EVP_PKEY_CTX_free(pctx);

EVP_PKEY_print_params(bio_out, param_key, 0, NULL);

A DSA key can be generated using domain parameters by calling:

EVP_PKEY *key = NULL;
EVP_PKEY_CTX *gctx = NULL;

gctx = EVP_PKEY_CTX_new_from_pkey(NULL, param_key, NULL);
EVP_PKEY_keygen_init(gctx);
EVP_PKEY_generate(gctx, &key);
EVP_PKEY_CTX_free(gctx);
EVP_PKEY_print_private(bio_out, key, 0, NULL);

⭐ CONFORMING TO ⭐

The following sections of FIPS186-4:

  • A.1.1.2 Generation of Probable Primes p and q Using an Approved Hash Function.
  • A.2.3 Generation of canonical generator g.
  • A.2.1 Unverifiable Generation of the Generator g.

🦋 SEE ALSO 🦋

EVP_PKEY-FFC(7), EVP_SIGNATURE-DSA(7), EVP_PKEY(3), provider-keymgmt(7), EVP_KEYMGMT(3), OSSL_PROVIDER-default(7), OSSL_PROVIDER-FIPS(7)

🌈 HISTORY 🌈

DSA key generation and signature generation are no longer FIPS approved in OpenSSL 3.4. See "FIPS indicators" in fips_module(7) for more information.

Copyright 2020-2024 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 whole page bestie — this one's from version 4.0.3, dated 2026-09-29, so like, go read your FFC parameters and stay validated 🫶✨

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