EVP_PKEY-FFC - EVP_PKEY DSA and DH/DHX shared FFC parameters.
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.
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Reserved.
Licensed under the Apache License 2.0 (the "License").
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