# EVP_PKEY-FFC - EVP_PKEY DSA and DH/DHX shared FFC parameters. - man(7ssl) - [phpMan] [_EVP_PKEY-FFC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPPKEY-FFC/7SSL/markdown) OpenSSL [_EVP_PKEY-FFC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPPKEY-FFC/7SSL/markdown) ## NAME EVP_PKEY-FFC - EVP_PKEY DSA and DH/DHX shared FFC parameters. ## DESCRIPTION Finite field cryptography (FFC) is a method of implementing discrete logarithm cryptography using finite field mathematics. DSA is an example of FFC and Diffie-Hellman key establishment algorithms specified in SP800-56A can also be implemented as FFC. The **DSA**, **DH **and **DHX **keytypes are implemented in OpenSSL's default and FIPS providers. The implementations support the basic DSA, DH and DHX keys, containing the public and private keys _pub_ and _priv_ as well as the three main domain parameters _p_, _q_ and _g_. For **DSA **(and **DH **that is not a named group) 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 **DH **the _seed_ and _pcounter_ can be stored in ASN1 data (but the _gindex_ is not). For **DSA **however, these fields are not stored in the ASN1 data so they need to be stored externally if validation is required. The **DH **key type uses PKCS#3 format which saves p and g, but not the 'q' value. The **DHX **key type uses X9.42 format which saves the value of 'q' and this must be used for FIPS186-4. ### FFC parameters In addition to the common parameters that all keytypes should support (see "Common parameters" in [**provider-keymgmt**(7)](https://www.chedong.com/phpMan.php/man/provider-keymgmt/7/markdown)), the **DSA**, **DH **and **DHX **keytype implementations support the following. "pub" (**OSSL_PKEY_PARAM_PUB_KEY**) The public key value. "priv" (**OSSL_PKEY_PARAM_PRIV_KEY**) The private key value. ### FFC DSA, DH and DHX domain parameters "p" (**OSSL_PKEY_PARAM_FFC_P**) A DSA or Diffie-Hellman prime "p" value. "g" (**OSSL_PKEY_PARAM_FFC_G**) A DSA or Diffie-Hellman generator "g" value. ### FFC DSA and DHX domain parameters "q" (**OSSL_PKEY_PARAM_FFC_Q**) A DSA or Diffie-Hellman prime "q" value. "seed" (**OSSL_PKEY_PARAM_FFC_SEED**) An optional domain parameter _seed_ value used during generation and validation of _p_, _q_ and canonical _g_. For validation this needs to set the _seed_ that was produced during generation. "gindex" (**OSSL_PKEY_PARAM_FFC_GINDEX**) Sets the index to use for canonical generation and verification of the generator _g_. Set this to a positive value from 0..FF to use this mode. This _gindex_ can then be reused during key validation to verify the value of _g_. If this value is not set or is -1 then unverifiable generation of the generator _g_ will be used. "pcounter" (**OSSL_PKEY_PARAM_FFC_PCOUNTER**) An optional domain parameter _counter_ value that is output during generation of _p_. This value must be saved if domain parameter validation is required. "hindex" (**OSSL_PKEY_PARAM_FFC_H**) For unverifiable generation of the generator _g_ this value is output during generation of _g_. Its value is the first integer larger than one that satisfies g = h^j mod p (where g != 1 and "j" is the cofactor). "j" (**OSSL_PKEY_PARAM_FFC_COFACTOR**) An optional informational cofactor parameter that should equal to (p - 1) / q. "validate-pq" (**OSSL_PKEY_PARAM_FFC_VALIDATE_PQ**) "validate-g" (**OSSL_PKEY_PARAM_FFC_VALIDATE_G**) These boolean values are used during FIPS186-4 or FIPS186-2 key validation checks (See [**EVP_PKEY_param_check**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYparamcheck/3/markdown)) to select validation options. By default _validate-pq_ and _validate-g_ are both set to 1 to check that p,q and g are valid. Either of these may be set to 0 to skip a test, which is mainly useful for testing purposes. "validate-legacy" (**OSSL_PKEY_PARAM_FFC_VALIDATE_LEGACY**) This boolean value is used during key validation checks (See [**EVP_PKEY_param_check**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYparamcheck/3/markdown)) to select the validation type. The default value of 0 selects FIPS186-4 validation. Setting this value to 1 selects FIPS186-2 validation. ### FFC key generation parameters The following key generation types are available for DSA and DHX algorithms: "type" (**OSSL_PKEY_PARAM_FFC_TYPE**) Sets the type of parameter generation. The shared valid values are: "fips186_4" The current standard. "fips186_2" The old standard that should only be used for legacy purposes. "default" This can choose one of "fips186_4" or "fips186_2" depending on other parameters set for parameter generation. "pbits" (**OSSL_PKEY_PARAM_FFC_PBITS**) Sets the size (in bits) of the prime 'p'. "qbits" (**OSSL_PKEY_PARAM_FFC_QBITS**) Sets the size (in bits) of the prime 'q'. For "fips186_4" this can be either 224 or 256. For "fips186_2" this has a size of 160. "digest" (**OSSL_PKEY_PARAM_FFC_DIGEST**) Sets the Digest algorithm to be used as part of the Key Generation Function associated with the given Key Generation _ctx_. This must also be set for key validation. "properties" (**OSSL_PKEY_PARAM_FFC_DIGEST_PROPS**) Sets properties to be used upon look up of the implementation for the selected Digest algorithm for the Key Generation Function associated with the given key generation _ctx_. This may also be set for key validation. "seed" (**OSSL_PKEY_PARAM_FFC_SEED**) For "fips186_4" or "fips186_2" generation this sets the _seed_ data to use instead of generating a random seed internally. This should be used for testing purposes only. This will either produce fixed values for the generated parameters OR it will fail if the seed did not generate valid primes. "gindex" (**OSSL_PKEY_PARAM_FFC_GINDEX**) "pcounter" (**OSSL_PKEY_PARAM_FFC_PCOUNTER**) "hindex" (**OSSL_PKEY_PARAM_FFC_H**) These types are described above. ## CONFORMING TO The following sections of SP800-56Ar3: 5.5.1.1 FFC Domain Parameter Selection/Generation 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-DSA**(7)](https://www.chedong.com/phpMan.php/man/EVPPKEY-DSA/7/markdown), [**EVP_PKEY-DH**(7)](https://www.chedong.com/phpMan.php/man/EVPPKEY-DH/7/markdown), [**EVP_SIGNATURE-DSA**(7)](https://www.chedong.com/phpMan.php/man/EVPSIGNATURE-DSA/7/markdown), [**EVP_KEYEXCH-DH**(7)](https://www.chedong.com/phpMan.php/man/EVPKEYEXCH-DH/7/markdown) [**EVP_KEYMGMT**(3)](https://www.chedong.com/phpMan.php/man/EVPKEYMGMT/3/markdown), [**EVP_PKEY**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEY/3/markdown), [**provider-keymgmt**(7)](https://www.chedong.com/phpMan.php/man/provider-keymgmt/7/markdown), [**OSSL_PROVIDER-default**(7)](https://www.chedong.com/phpMan.php/man/OSSLPROVIDER-default/7/markdown), [**OSSL_PROVIDER-FIPS**(7)](https://www.chedong.com/phpMan.php/man/OSSLPROVIDER-FIPS/7/markdown), ## 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 <>. 3.0.13 2026-07-29 [_EVP_PKEY-FFC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPPKEY-FFC/7SSL/markdown)