mirror of https://github.com/openssl/openssl
278 lines
8.7 KiB
Plaintext
278 lines
8.7 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY-DH, EVP_KEYMGMT-DH - EVP_PKEY DH keytype and algorithm support
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=head1 DESCRIPTION
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For B<DH> FFC key agreement, two classes of domain parameters can be used:
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"safe" domain parameters that are associated with approved named safe-prime
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groups, and a class of "FIPS 186-type" domain parameters. FIPS 186-type domain
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parameters should only be used for backward compatibility with existing
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applications that cannot be upgraded to use the approved safe-prime groups.
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See L<EVP_PKEY-FFC(7)> for more information about FFC keys.
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For B<DH> that is not a named group the FIPS186-4 standard specifies that the
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values used for FFC parameter generation are also required for parameter
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validation. This means that optional FFC domain parameter values for
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I<seed>, I<pcounter> and I<gindex> may need to be stored for validation purposes.
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For B<DH> the I<seed> and I<pcounter> can be stored in ASN1 data
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(but the I<gindex> is not).
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=head2 DH parameters
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In addition to the common FCC parameters that all FFC keytypes should support
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(see L<EVP_PKEY-FFC(7)/FFC parameters>) the B<DH> keytype
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implementation supports the following:
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=over 4
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=item "group" (B<OSSL_PKEY_PARAM_GROUP_NAME>) <UTF8 string>
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Set or gets a string that associates a B<DH> named safe prime group with known
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values for I<p>, I<q> and I<g>.
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The following values can be used by the OpenSSL's default and FIPS providers:
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"ffdhe2048", "ffdhe3072", "ffdhe4096", "ffdhe6144", "ffdhe8192",
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"modp_2048", "modp_3072", "modp_4096", "modp_6144", "modp_8192".
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The following additional values can also be used by OpenSSL's default provider:
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"modp_1536", "dh_1024_160", "dh_2048_224", "dh_2048_256".
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DH named groups can be easily validated since the parameters are well known.
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For protocols that only transfer I<p> and I<g> the value of I<q> can also be
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retrieved.
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=item "safeprime-generator" (B<OSSL_PKEY_PARAM_DH_GENERATOR>) <integer>
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Used for DH generation of safe primes using the old generator code.
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It is recommended to use a named safe prime group instead, if domain parameter
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validation is required. The default value is 2.
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These are not named safe prime groups so setting this value for the OpenSSL FIPS
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provider will instead choose a named safe prime group based on the size of I<p>.
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=item "encoded-pub-key" (B<OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY>) <octet string>
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Used for getting and setting the encoding of the DH public key used in a key
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exchange message for the TLS protocol.
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=back
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=head2 DH domain parameter / key generation parameters
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In addition to the common FFC key generation parameters that all FFC key types
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should support (see L<EVP_PKEY-FFC(7)/FFC key generation parameters>) the
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B<DH> keytype implementation supports the following:
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=over 4
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=item "type" (B<OSSL_PKEY_PARAM_FFC_TYPE>) <utf8_string>
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Sets the type of parameter generation. For B<DH> valid values are:
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=over 4
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=item "fips186_4"
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=item "default"
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=item "fips186_2"
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These are described in L<EVP_PKEY-FFC(7)/FFC key generation parameters>
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=item "group"
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This specifies that a named safe prime name will be chosen using the "pbits"
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type.
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=item "generator"
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A safe prime generator. See the "safeprime-generator" type above.
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=back
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=item "pbits" (B<OSSL_PKEY_PARAM_FFC_PBITS>) <unsigned integer>
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Sets the size (in bits) of the prime 'p'.
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For "fips186_4" this must be 2048.
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For "fips186_2" this must be 1024.
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For "group" this can be any one of 2048, 3072, 4096, 6144 or 8192.
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=item "priv_len" (B<OSSL_PKEY_PARAM_DH_PRIV_LEN>) <integer>
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An optional value to set the maximum length of the generated private key.
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The default value used if this is not set is the maximum value of
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BN_num_bits(I<q>)). The minimum value that this can be set to is 2 * s.
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Where s is the security strength of the key which has values of
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112, 128, 152, 176 and 200 for key sizes of 2048, 3072, 4096, 6144 and 8192.
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=back
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=head1 EXAMPLES
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An B<EVP_PKEY> context can be obtained by calling:
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EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_from_name(NULL, "DH", NULL);
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A B<DH> key can be generated with a named safe prime group by calling:
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int priv_len = 2 * 112;
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OSSL_PARAM params[3];
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EVP_PKEY *pkey = NULL;
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EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_from_name(NULL, "DH", NULL);
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params[0] = OSSL_PARAM_construct_utf8_string("group", "ffdhe2048", 0);
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/* "priv_len" is optional */
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params[1] = OSSL_PARAM_construct_int("priv_len", &priv_len);
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params[2] = OSSL_PARAM_construct_end();
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EVP_PKEY_keygen_init(pctx);
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EVP_PKEY_CTX_set_params(pctx, params);
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EVP_PKEY_gen(pctx, &pkey);
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...
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EVP_PKEY_free(key);
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EVP_PKEY_CTX_free(pctx);
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B<DHX> domain parameters can be generated according to B<FIPS 186-4> by calling:
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unsigned int pbits = 2048;
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unsigned int qbits = 256;
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OSSL_PARAM params[5];
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EVP_PKEY *param_key = NULL;
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EVP_PKEY_CTX *pctx = NULL;
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pctx = EVP_PKEY_CTX_new_from_name(NULL, "DHX", NULL);
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EVP_PKEY_paramgen_init(pctx);
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params[0] = OSSL_PARAM_construct_uint("pbits", &pbits);
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params[1] = OSSL_PARAM_construct_uint("qbits", &qbits);
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params[2] = OSSL_PARAM_construct_utf8_string("type", "fips186_4", 0);
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params[3] = OSSL_PARAM_construct_utf8_string("digest", "SHA256", 0);
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params[4] = OSSL_PARAM_construct_end();
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EVP_PKEY_CTX_set_params(pctx, params);
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EVP_PKEY_gen(pctx, ¶m_key);
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EVP_PKEY_print_params(bio_out, param_key, 0, NULL);
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...
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EVP_PKEY_free(param_key);
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EVP_PKEY_CTX_free(pctx);
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A B<DH> key can be generated using domain parameters by calling:
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EVP_PKEY *key = NULL;
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EVP_PKEY_CTX *gctx = EVP_PKEY_CTX_new_from_pkey(NULL, param_key, NULL);
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EVP_PKEY_keygen_init(gctx);
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EVP_PKEY_gen(gctx, &key);
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EVP_PKEY_print_private(bio_out, key, 0, NULL);
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...
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EVP_PKEY_free(key);
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EVP_PKEY_CTX_free(gctx);
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To validate B<FIPS 186-4> B<DHX> domain parameters decoded from B<PEM> or
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B<DER> data, additional values used during generation may be required to
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be set into the key.
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EVP_PKEY_todata(), OSSL_PARAM_merge(), and EVP_PKEY_fromdata() are useful
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to add these parameters to the original key or domain parameters before
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the actual validation.
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EVP_PKEY *received_domp = ...; /* parameters received and decoded */
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unsigned char *seed = ...; /* and additional parameters received */
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size_t seedlen = ...; /* by other means, required */
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int gindex = ...; /* for the validation */
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int pcounter = ...;
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int hindex = ...;
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OSSL_PARAM extra_params[5];
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OSSL_PARAM *domain_params = NULL;
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OSSL_PARAM *merged_params = NULL;
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EVP_PKEY_CTX *ctx = NULL, *validate_ctx = NULL;
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EVP_PKEY *complete_domp = NULL;
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EVP_PKEY_todata(received_domp, OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS,
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&domain_params);
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extra_params[0] = OSSL_PARAM_construct_octet_string("seed", seed, seedlen);
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extra_params[1] = OSSL_PARAM_construct_int("gindex", &gindex);
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extra_params[2] = OSSL_PARAM_construct_int("pcounter", &pcounter);
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extra_params[3] = OSSL_PARAM_construct_int("hindex", &hindex);
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extra_params[4] = OSSL_PARAM_construct_end();
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merged_params = OSSL_PARAM_merge(domain_params, extra_params);
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ctx = EVP_PKEY_CTX_new_from_name(NULL, "DHX", NULL);
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EVP_PKEY_fromdata_init(ctx);
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EVP_PKEY_fromdata(ctx, &complete_domp, OSSL_KEYMGMT_SELECT_ALL,
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merged_params);
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validate_ctx = EVP_PKEY_CTX_new_from_pkey(NULL, complete_domp, NULL);
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if (EVP_PKEY_param_check(validate_ctx) > 0)
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/* validation_passed(); */
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else
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/* validation_failed(); */
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OSSL_PARAM_free(domain_params);
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OSSL_PARAM_free(merged_params);
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EVP_PKEY_CTX_free(ctx);
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EVP_PKEY_CTX_free(validate_ctx);
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EVP_PKEY_free(complete_domp);
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=head1 CONFORMING TO
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=over 4
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=item RFC 7919 (TLS ffdhe named safe prime groups)
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=item RFC 3526 (IKE modp named safe prime groups)
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=item RFC 5114 (Additional DH named groups for dh_1024_160", "dh_2048_224"
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and "dh_2048_256").
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=back
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The following sections of SP800-56Ar3:
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=over 4
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=item 5.5.1.1 FFC Domain Parameter Selection/Generation
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=item Appendix D: FFC Safe-prime Groups
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=back
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The following sections of FIPS 186-4:
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=over 4
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=item A.1.1.2 Generation of Probable Primes p and q Using an Approved Hash Function.
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=item A.2.3 Generation of canonical generator g.
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=item A.2.1 Unverifiable Generation of the Generator g.
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=back
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=head1 SEE ALSO
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L<EVP_PKEY-FFC(7)>,
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L<EVP_KEYEXCH-DH(7)>
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L<EVP_PKEY(3)>,
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L<provider-keymgmt(7)>,
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L<EVP_KEYMGMT(3)>,
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L<OSSL_PROVIDER-default(7)>,
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L<OSSL_PROVIDER-FIPS(7)>
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=head1 COPYRIGHT
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Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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