EVP_PKEY-FFC(7SSL) OpenSSL EVP_PKEY-FFC(7SSL)
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)), the DSA, DH and DHX
keytype implementations support the following.
"pub" (OSSL_PKEY_PARAM_PUB_KEY) <unsigned integer>
The public key value.
"priv" (OSSL_PKEY_PARAM_PRIV_KEY) <unsigned integer>
The private key value.
FFC DSA, DH and DHX domain parameters
"p" (OSSL_PKEY_PARAM_FFC_P) <unsigned integer>
A DSA or Diffie-Hellman prime "p" value.
"g" (OSSL_PKEY_PARAM_FFC_G) <unsigned integer>
A DSA or Diffie-Hellman generator "g" value.
FFC DSA and DHX domain parameters
"q" (OSSL_PKEY_PARAM_FFC_Q) <unsigned integer>
A DSA or Diffie-Hellman prime "q" value.
"seed" (OSSL_PKEY_PARAM_FFC_SEED) <octet string>
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) <integer>
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) <integer>
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) <integer>
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) <unsigned integer>
An optional informational cofactor parameter that should equal to (p
- 1) / q.
"validate-pq" (OSSL_PKEY_PARAM_FFC_VALIDATE_PQ) <unsigned integer>
"validate-g" (OSSL_PKEY_PARAM_FFC_VALIDATE_G) <unsigned integer>
These boolean values are used during FIPS186-4 or FIPS186-2 key
validation checks (See EVP_PKEY_param_check(3)) 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) <unsigned
integer>
This boolean value is used during key validation checks (See
EVP_PKEY_param_check(3)) 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) <UTF8 string>
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) <unsigned integer>
Sets the size (in bits) of the prime 'p'.
"qbits" (OSSL_PKEY_PARAM_FFC_QBITS) <unsigned integer>
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) <UTF8 string>
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) <UTF8 string>
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) <octet string>
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) <integer>
"pcounter" (OSSL_PKEY_PARAM_FFC_PCOUNTER) <integer>
"hindex" (OSSL_PKEY_PARAM_FFC_H) <integer>
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), EVP_PKEY-DH(7), EVP_SIGNATURE-DSA(7),
EVP_KEYEXCH-DH(7), EVP_KEYMGMT(3), EVP_PKEY(3), provider-keymgmt(7),
OSSL_PROVIDER-default(7), OSSL_PROVIDER-FIPS(7),
COPYRIGHT
Copyright 2020-2025 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>.
3.5.4 2025-09-30 EVP_PKEY-FFC(7SSL)
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