EVP_PKEY-EC(7ossl)

📦 version 14.5, in freebsd 14.5

✨ EVP_PKEY-EC, EVP_KEYMGMT-EC — the EC keytype and algorithm support page ✨

okay bestie, this is the 7ossl manual page for EVP_PKEY-EC and EVP_KEYMGMT-EC, and it's literally the whole vibe of how elliptic curve keys work in OpenSSL. grab a strawberry drink 🍓 and let's go.

🌸 NAME 🌸

EVP_PKEY-EC, EVP_KEYMGMT-EC — the EVP_PKEY EC keytype and algorithm support. that's the whole title, no cap 💅

🎀 DESCRIPTION 🎀

The EC keytype lives in OpenSSL's default provider. that's it, that's the home base 🏠

💜 Common EC parameters 💜

so the normal way to specify domain parameters for an EC curve is via the curve name "group". iconic. but for curves with no curve name, you can use explicit parameters that specify "field-type", "p", "a", "b", "generator" and "order". these explicit parameters are supported for backwards compatibility reasons, but heads up — they are not compliant with multiple standards (including RFC5915) which only allow named curves. so like, they exist, but they're kinda the deprecated friend of the group 🙈

The following KeyGen/Gettable/Import/Export types are available for the built-in EC algorithm:

"group" (OSSL_PKEY_PARAM_GROUP_NAME) <UTF8 string> — the curve name. simple, elegant, main character energy ✨
"field-type" (OSSL_PKEY_PARAM_EC_FIELD_TYPE) <UTF8 string> — the value should be either "prime-field" or "characteristic-two-field", which correspond to prime field Fp and binary field F2^m. pick your fighter 🥊
"p" (OSSL_PKEY_PARAM_EC_P) <unsigned integer> — 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. math girlie things 💖
"a" (OSSL_PKEY_PARAM_EC_A) <unsigned integer>
"b" (OSSL_PKEY_PARAM_EC_B) <unsigned integer>
"seed" (OSSL_PKEY_PARAM_EC_SEED) <octet string>

so a and b represent 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. cute lore, honestly 🦋

"generator" (OSSL_PKEY_PARAM_EC_GENERATOR) <octet string>
"order" (OSSL_PKEY_PARAM_EC_ORDER) <unsigned integer>
"cofactor" (OSSL_PKEY_PARAM_EC_COFACTOR) <unsigned integer>

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. slay 🔥

"decoded-from-explicit" (OSSL_PKEY_PARAM_EC_DECODED_FROM_EXPLICIT_PARAMS) <integer> — 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. the receipts, basically 🧾
"use-cofactor-flag" (OSSL_PKEY_PARAM_USE_COFACTOR_ECDH) <integer> — 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) for the related OSSL_EXCHANGE_PARAM_EC_ECDH_COFACTOR_MODE parameter that can be set on a per-operation basis. per-operation settings? we love flexibility 💅
"encoding" (OSSL_PKEY_PARAM_EC_ENCODING) <UTF8 string> — Set the format used for serializing the EC group parameters. Valid values are "explicit" or "named_curve". The default value is "named_curve". the default ate, honestly 👑
"point-format" (OSSL_PKEY_PARAM_EC_POINT_CONVERSION_FORMAT) <UTF8 string> — Sets or gets the point_conversion_form for the key. For a description of point_conversion_forms please see EC_POINT_new(3). Valid values are "uncompressed" or "compressed". The default value is "uncompressed".
"group-check" (OSSL_PKEY_PARAM_EC_GROUP_CHECK_TYPE) <UTF8 string> — 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. iykyk 🌈
"include-public" (OSSL_PKEY_PARAM_EC_INCLUDE_PUBLIC) <integer> — 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. keep your secrets secret, bestie 🤫
"pub" (OSSL_PKEY_PARAM_PUB_KEY) <octet string> — 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. ⚠️ the glow-up is real

"priv" (OSSL_PKEY_PARAM_PRIV_KEY) <unsigned integer> — The private key value. that's it, that's the whole thing 🎀
"encoded-pub-key" (OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY) <octet string> — 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) <unsigned integer> — Used for getting the EC public key X component ✨
"qy" (OSSL_PKEY_PARAM_EC_PUB_Y) <unsigned integer> — Used for getting the EC public key Y component ✨
"default-digest" (OSSL_PKEY_PARAM_DEFAULT_DIGEST) <UTF8 string> — Getter that returns the default digest name. (Currently returns "SHA256" as of OpenSSL 3.0). she's consistent, we stan 💖

The following Gettable types are also available for the built-in EC algorithm:

"basis-type" (OSSL_PKEY_PARAM_EC_CHAR2_TYPE) <UTF8 string> — 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) <integer>
"tp" (OSSL_PKEY_PARAM_EC_CHAR2_TP_BASIS) <integer>
"k1" (OSSL_PKEY_PARAM_EC_CHAR2_PP_K1) <integer>
"k2" (OSSL_PKEY_PARAM_EC_CHAR2_PP_K2) <integer>
"k3" (OSSL_PKEY_PARAM_EC_CHAR2_PP_K3) <integer>

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. the inequality chains are giving math class but make it fashion 💀

🦋 EC key validation 🦋

For EC keys, EVP_PKEY_param_check(3) behaves in the following way: For the OpenSSL default provider it uses either EC_GROUP_check(3) or EC_GROUP_check_named_curve(3) depending on the flag EC_FLAG_CHECK_NAMED_GROUP. The OpenSSL FIPS provider uses EC_GROUP_check_named_curve(3) in order to conform to SP800-56Ar3 Assurances of Domain-Parameter Validity. compliance queen 👑

For EC keys, EVP_PKEY_param_check_quick(3) is equivalent to EVP_PKEY_param_check(3). literally the same thing, no notes 💅

For EC keys, EVP_PKEY_public_check(3) and EVP_PKEY_public_check_quick(3) conform to SP800-56Ar3 ECC Full Public-Key Validation and ECC Partial Public-Key Validation respectively.

For EC Keys, EVP_PKEY_private_check(3) and EVP_PKEY_pairwise_check(3) 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), EVP_KEYMGMT(3), EVP_PKEY(3), provider-keymgmt(7), EVP_SIGNATURE-ECDSA(7), EVP_KEYEXCH-ECDH(7) — go read these next, bestie, they're all linked in the group chat 🫶

👑 COPYRIGHT 👑

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>.

okay that's the whole page, mwah 💋 this was OpenSSL 3.0.21, dated 2026-06-09, from the EVP_PKEY-EC(7ossl) manual — go forth and generate keys, icon 💖✨

📦 where this page comes from

freebsd 14.5: base 14.5
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms