NAME

       EVP_PKEY-DSA, EVP_KEYMGMT-DSA - EVP_PKEY DSA keytype and algorithm support

DESCRIPTION

       For DSA the FIPS186-4 standard specifies that the values used for FFC parameter generation are also
       required for parameter validation.  This means that optional FFC domain parameter values for seed,
       pcounter and gindex may need to be stored for validation purposes. For DSA these fields are not stored in
       the ASN1 data so they need to be stored externally if validation is required.

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

       The following restrictions apply to the "pbits" field:

       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.

   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 (see 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)

COPYRIGHT

       Copyright 2020-2022 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>.

3.0.13                                             2025-02-05                                 EVP_PKEY-DSA(7SSL)