# man > EVP_PKEY-EC(7) [_EVP_PKEY-EC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPPKEY-EC/7SSL/markdown) OpenSSL [_EVP_PKEY-EC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPPKEY-EC/7SSL/markdown) ## NAME EVP_PKEY-EC, EVP_KEYMGMT-EC - EVP_PKEY EC keytype and algorithm support ## DESCRIPTION The **EC **keytype is implemented in OpenSSL's default provider. ### Common EC parameters The normal way of specifying domain parameters for an EC curve is via the curve name "group". For curves with no curve name, explicit parameters can be used that specify "field-type", "p", "a", "b", "generator" and "order". Explicit parameters are supported for backwards compatibility reasons, but they are not compliant with multiple standards (including RFC5915) which only allow named curves. The following KeyGen/Gettable/Import/Export types are available for the built-in EC algorithm: "group" (**OSSL_PKEY_PARAM_GROUP_NAME**) The curve name. "field-type" (**OSSL_PKEY_PARAM_EC_FIELD_TYPE**) The value should be either "prime-field" or "characteristic-two-field", which correspond to prime field Fp and binary field F2^m. "p" (**OSSL_PKEY_PARAM_EC_P**) For a curve over Fp _p_ is the prime for the field. For a curve over F2^m _p_ represents the irreducible polynomial - each bit represents a term in the polynomial. Therefore, there will either be three or five bits set dependent on whether the polynomial is a trinomial or a pentanomial. "a" (**OSSL_PKEY_PARAM_EC_A**) "b" (**OSSL_PKEY_PARAM_EC_B**) "seed" (**OSSL_PKEY_PARAM_EC_SEED**) _a_ and _b_ represents the coefficients of the curve For Fp: y^2 mod p = x^3 +ax + b mod p OR For F2^m: y^2 + xy = x^3 + ax^2 + b _seed_ is an optional value that is for information purposes only. It represents the random number seed used to generate the coefficient _b_ from a random number. "generator" (**OSSL_PKEY_PARAM_EC_GENERATOR**) "order" (**OSSL_PKEY_PARAM_EC_ORDER**) "cofactor" (**OSSL_PKEY_PARAM_EC_COFACTOR**) The _generator_ is a well defined point on the curve chosen for cryptographic operations. The encoding conforms with Sec. 2.3.3 of the SECG SEC 1 ("Elliptic Curve Cryptography") standard. See **EC_POINT_oct2point()**. Integers used for point multiplications will be between 0 and _order_ - 1. _cofactor_ is an optional value. _order_ multiplied by the _cofactor_ gives the number of points on the curve. "decoded-from-explicit" (**OSSL_PKEY_PARAM_EC_DECODED_FROM_EXPLICIT_PARAMS**) Gets a flag indicating whether the key or parameters were decoded from explicit curve parameters. Set to 1 if so or 0 if a named curve was used. "use-cofactor-flag" (**OSSL_PKEY_PARAM_USE_COFACTOR_ECDH**) Enable Cofactor DH (ECC CDH) if this value is 1, otherwise it uses normal EC DH if the value is zero. The cofactor variant multiplies the shared secret by the EC curve's cofactor (note for some curves the cofactor is 1). See also [**EVP_KEYEXCH-ECDH**(7)](https://www.chedong.com/phpMan.php/man/EVPKEYEXCH-ECDH/7/markdown) for the related **OSSL_EXCHANGE_PARAM_EC_ECDH_COFACTOR_MODE** parameter that can be set on a per-operation basis. "encoding" (**OSSL_PKEY_PARAM_EC_ENCODING**) Set the format used for serializing the EC group parameters. Valid values are "explicit" or "named_curve". The default value is "named_curve". "point-format" (**OSSL_PKEY_PARAM_EC_POINT_CONVERSION_FORMAT**) Sets or gets the point_conversion_form for the _key_. For a description of point_conversion_forms please see [**EC_POINT_new**(3)](https://www.chedong.com/phpMan.php/man/ECPOINTnew/3/markdown). Valid values are "uncompressed" or "compressed". The default value is "uncompressed". "group-check" (**OSSL_PKEY_PARAM_EC_GROUP_CHECK_TYPE**) Sets or Gets the type of group check done when **EVP_PKEY_param_check() **is called. Valid values are "default", "named" and "named-nist". The "named" type checks that the domain parameters match the inbuilt curve parameters, "named-nist" is similar but also checks that the named curve is a nist curve. The "default" type does domain parameter validation for the OpenSSL default provider, but is equivalent to "named-nist" for the OpenSSL FIPS provider. "include-public" (**OSSL_PKEY_PARAM_EC_INCLUDE_PUBLIC**) Setting this value to 0 indicates that the public key should not be included when encoding the private key. The default value of 1 will include the public key. "pub" (**OSSL_PKEY_PARAM_PUB_KEY**) The public key value in encoded EC point format conforming to Sec. 2.3.3 and 2.3.4 of the SECG SEC 1 ("Elliptic Curve Cryptography") standard. This parameter is used when importing or exporting the public key value with the **EVP_PKEY_fromdata() **and **EVP_PKEY_todata() **functions. Note, in particular, that the choice of point compression format used for encoding the exported value via **EVP_PKEY_todata() **depends on the underlying provider implementation. Before OpenSSL 3.0.8, the implementation of providers included with OpenSSL always opted for an encoding in compressed format, unconditionally. Since OpenSSL 3.0.8, the implementation has been changed to honor the **OSSL_PKEY_PARAM_EC_POINT_CONVERSION_FORMAT** parameter, if set, or to default to uncompressed format. "priv" (**OSSL_PKEY_PARAM_PRIV_KEY**) The private key value. "encoded-pub-key" (**OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY**) Used for getting and setting the encoding of an EC public key. The public key is expected to be a point conforming to Sec. 2.3.4 of the SECG SEC 1 ("Elliptic Curve Cryptography") standard. "qx" (**OSSL_PKEY_PARAM_EC_PUB_X**) Used for getting the EC public key X component. "qy" (**OSSL_PKEY_PARAM_EC_PUB_Y**) Used for getting the EC public key Y component. "default-digest" (**OSSL_PKEY_PARAM_DEFAULT_DIGEST**) Getter that returns the default digest name. (Currently returns "SHA256" as of OpenSSL 3.0). The following Gettable types are also available for the built-in EC algorithm: "basis-type" (**OSSL_PKEY_PARAM_EC_CHAR2_TYPE**) Supports the values "tpBasis" for a trinomial or "ppBasis" for a pentanomial. This field is only used for a binary field F2^m. "m" (**OSSL_PKEY_PARAM_EC_CHAR2_M**) "tp" (**OSSL_PKEY_PARAM_EC_CHAR2_TP_BASIS**) "k1" (**OSSL_PKEY_PARAM_EC_CHAR2_PP_K1**) "k2" (**OSSL_PKEY_PARAM_EC_CHAR2_PP_K2**) "k3" (**OSSL_PKEY_PARAM_EC_CHAR2_PP_K3**) These fields are only used for a binary field F2^m. _m_ is the degree of the binary field. _tp_ is the middle bit of a trinomial so its value must be in the range m > tp > 0. _k1_, _k2_ and _k3_ are used to get the middle bits of a pentanomial such that m > k3 > k2 > k1 > 0 ### EC key validation For EC keys, [**EVP_PKEY_param_check**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYparamcheck/3/markdown) behaves in the following way: For the OpenSSL default provider it uses either [**EC_GROUP_check**(3)](https://www.chedong.com/phpMan.php/man/ECGROUPcheck/3/markdown) or [**EC_GROUP_check_named_curve**(3)](https://www.chedong.com/phpMan.php/man/ECGROUPchecknamedcurve/3/markdown) depending on the flag EC_FLAG_CHECK_NAMED_GROUP. The OpenSSL FIPS provider uses [**EC_GROUP_check_named_curve**(3)](https://www.chedong.com/phpMan.php/man/ECGROUPchecknamedcurve/3/markdown) in order to conform to SP800-56Ar3 _Assurances_ _of_ _Domain-Parameter_ _Validity_. For EC keys, [**EVP_PKEY_param_check_quick**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYparamcheckquick/3/markdown) is equivalent to [**EVP_PKEY_param_check**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYparamcheck/3/markdown). For EC keys, [**EVP_PKEY_public_check**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYpubliccheck/3/markdown) and [**EVP_PKEY_public_check_quick**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYpubliccheckquick/3/markdown) conform to SP800-56Ar3 _ECC_ _Full_ _Public-Key_ _Validation_ and _ECC_ _Partial_ _Public-Key_ _Validation_ respectively. For EC Keys, [**EVP_PKEY_private_check**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYprivatecheck/3/markdown) and [**EVP_PKEY_pairwise_check**(3)](https://www.chedong.com/phpMan.php/man/EVPPKEYpairwisecheck/3/markdown) conform to SP800-56Ar3 _Private_ _key_ _validity_ and _Owner_ _Assurance_ _of_ _Pair-wise_ _Consistency_ respectively. ## EXAMPLES An **EVP_PKEY **context can be obtained by calling: EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_from_name(NULL, "EC", NULL); An **EVP_PKEY **ECDSA or ECDH key can be generated with a "P-256" named group by calling: pkey = EVP_EC_gen("P-256"); or like this: EVP_PKEY *key = NULL; OSSL_PARAM params[2]; EVP_PKEY_CTX *gctx = EVP_PKEY_CTX_new_from_name(NULL, "EC", NULL); EVP_PKEY_keygen_init(gctx); params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME, "P-256", 0); params[1] = OSSL_PARAM_construct_end(); EVP_PKEY_CTX_set_params(gctx, params); EVP_PKEY_generate(gctx, &key); EVP_PKEY_print_private(bio_out, key, 0, NULL); ... EVP_PKEY_free(key); EVP_PKEY_CTX_free(gctx); An **EVP_PKEY **EC CDH (Cofactor Diffie-Hellman) key can be generated with a "K-571" named group by calling: int use_cdh = 1; EVP_PKEY *key = NULL; OSSL_PARAM params[3]; EVP_PKEY_CTX *gctx = EVP_PKEY_CTX_new_from_name(NULL, "EC", NULL); EVP_PKEY_keygen_init(gctx); params[0] = OSSL_PARAM_construct_utf8_string(OSSL_PKEY_PARAM_GROUP_NAME, "K-571", 0); /* * This curve has a cofactor that is not 1 - so setting CDH mode changes * the behaviour. For many curves the cofactor is 1 - so setting this has * no effect. */ params[1] = OSSL_PARAM_construct_int(OSSL_PKEY_PARAM_USE_COFACTOR_ECDH, &use_cdh); params[2] = OSSL_PARAM_construct_end(); EVP_PKEY_CTX_set_params(gctx, params); EVP_PKEY_generate(gctx, &key); EVP_PKEY_print_private(bio_out, key, 0, NULL); ... EVP_PKEY_free(key); EVP_PKEY_CTX_free(gctx); ## SEE ALSO [**EVP_EC_gen**(3)](https://www.chedong.com/phpMan.php/man/EVPECgen/3/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), [**EVP_SIGNATURE-ECDSA**(7)](https://www.chedong.com/phpMan.php/man/EVPSIGNATURE-ECDSA/7/markdown), [**EVP_KEYEXCH-ECDH**(7)](https://www.chedong.com/phpMan.php/man/EVPKEYEXCH-ECDH/7/markdown) ## COPYRIGHT Copyright 2020-2023 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-EC_(7SSL)](https://www.chedong.com/phpMan.php/man/EVPPKEY-EC/7SSL/markdown)