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 2020-2021 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>.