EC_GROUP_NEW(3SSL)

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version 4.0.3 · 14 versions
, in ubuntu stonking

🎀 EC_GROUP_NEW 🎀

okay bestie, sit DOWN because we're doing elliptic curve groups today 💖 this is EC_GROUP_NEW(3SSL) — the OpenSSL manual page for all the functions that make and destroy EC_GROUP objects. yes it's long. no I'm not sorry. it's giving main character energy.

✨ NAME ✨

The whole girlies squad — functions for creating and destroying EC_GROUP objects:

  • EC_GROUP_get_ecparameters — grab ya ECPARAMETERS
  • EC_GROUP_get_ecpkparameters — grab ya ECPKPARAMETERS
  • EC_GROUP_new_from_params — build a group from params
  • EC_GROUP_to_params — turn a group into params
  • EC_GROUP_new_from_ecparameters — build a group from ECPARAMETERS
  • EC_GROUP_new_from_ecpkparameters — build a group from ECPKPARAMETERS
  • EC_GROUP_new — the O.G. constructor (deprecated, we'll get to it 🙈)
  • EC_GROUP_free — bye bye memory
  • EC_GROUP_clear_free — deprecated bye bye memory
  • EC_GROUP_new_curve_GFp — quick curve over Fp
  • EC_GROUP_new_curve_GF2m — quick curve over F2^m
  • EC_GROUP_new_by_curve_name_ex — built-in curve, with libctx + propq
  • EC_GROUP_new_by_curve_name — built-in curve, default context
  • EC_GROUP_set_curve — set the curve params
  • EC_GROUP_get_curve — read the curve params
  • EC_GROUP_set_curve_GFp — synonym for the setter (deprecated)
  • EC_GROUP_get_curve_GFp — synonym for the getter (deprecated)
  • EC_GROUP_set_curve_GF2m — synonym for the setter (deprecated)
  • EC_GROUP_get_curve_GF2m — synonym for the getter (deprecated)
  • EC_get_builtin_curves — list every built-in curve
  • OSSL_EC_curve_nid2name — nid → name
  • EC_curve_nid2nist — nid → NIST name
  • EC_curve_nist2nid — NIST name → nid

🌸 SYNOPSIS 🌸

#include <openssl/ec.h>

EC_GROUP *EC_GROUP_new_from_params(const OSSL_PARAM params[],
                                   OSSL_LIB_CTX *libctx, const char *propq);
OSSL_PARAM *EC_GROUP_to_params(const EC_GROUP *group, OSSL_LIB_CTX *libctx,
                               const char *propq, BN_CTX *bnctx);
EC_GROUP *EC_GROUP_new_from_ecparameters(const ECPARAMETERS *params);
EC_GROUP *EC_GROUP_new_from_ecpkparameters(const ECPKPARAMETERS *params);
void EC_GROUP_free(EC_GROUP *group);

EC_GROUP *EC_GROUP_new_curve_GFp(const BIGNUM *p, const BIGNUM *a,
                                 const BIGNUM *b, BN_CTX *ctx);
EC_GROUP *EC_GROUP_new_curve_GF2m(const BIGNUM *p, const BIGNUM *a,
                                  const BIGNUM *b, BN_CTX *ctx);
EC_GROUP *EC_GROUP_new_by_curve_name_ex(OSSL_LIB_CTX *libctx, const char *propq,
                                        int nid);
EC_GROUP *EC_GROUP_new_by_curve_name(int nid);

int EC_GROUP_set_curve(EC_GROUP *group, const BIGNUM *p, const BIGNUM *a,
                       const BIGNUM *b, BN_CTX *ctx);
int EC_GROUP_get_curve(const EC_GROUP *group, BIGNUM *p, BIGNUM *a, BIGNUM *b,
                       BN_CTX *ctx);

ECPARAMETERS *EC_GROUP_get_ecparameters(const EC_GROUP *group,
                                        ECPARAMETERS *params);
ECPKPARAMETERS *EC_GROUP_get_ecpkparameters(const EC_GROUP *group,
                                            ECPKPARAMETERS *params);

size_t EC_get_builtin_curves(EC_builtin_curve *r, size_t nitems);
const char *OSSL_EC_curve_nid2name(int nid);
const char *EC_curve_nid2nist(int nid);
int EC_curve_nist2nid(const char *name);

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

EC_GROUP *EC_GROUP_new(const EC_METHOD *meth);
void EC_GROUP_clear_free(EC_GROUP *group);

int EC_GROUP_set_curve_GFp(EC_GROUP *group, const BIGNUM *p,
                           const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
int EC_GROUP_get_curve_GFp(const EC_GROUP *group, BIGNUM *p,
                           BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
int EC_GROUP_set_curve_GF2m(EC_GROUP *group, const BIGNUM *p,
                            const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
int EC_GROUP_get_curve_GF2m(const EC_GROUP *group, BIGNUM *p,
                            BIGNUM *a, BIGNUM *b, BN_CTX *ctx);

🦋 DESCRIPTION 🦋

okay so, inside the library there are two forms of elliptic curve that we care about, and you gotta know both or nothing makes sense.

💜 Form one: curves over the prime field Fp

The elements of Fp are the integers 0 to p-1, where p is a prime number. Slay. That gives us this revised elliptic curve equation:

y^2 mod p = x^3 +ax + b mod p

💜 Form two: curves over a binary field F2^m

Here the elements of the field are integers of length at most m bits. For this form the elliptic curve equation gets modified to:

y^2 + xy = x^3 + ax^2 + b (where b != 0)

Operations in a binary field are performed relative to an irreducible polynomial. All such curves with OpenSSL use a trinomial or a pentanomial for this parameter. noted. 💅

🫶 Making a group (the deprecated way, don't do this)

Although deprecated since OpenSSL 3.0 and it should no longer be used, a new curve can be constructed by calling EC_GROUP_new(), using the implementation provided by meth (see EC_GFp_simple_method(3)) and associated with the library context ctx (see OSSL_LIB_CTX(3)). The ctx parameter may be NULL, in which case the default library context is used. It is then necessary to call EC_GROUP_set_curve() to set the curve parameters.

lowkey a red flag: applications should instead use one of the other EC_GROUP_new_* constructors. periodt.

🫶 EC_GROUP_new_from_params()

Creates a group with parameters specified by params. The library context libctx (see OSSL_LIB_CTX(3)) and property query string propq are used to fetch algorithms from providers. params may be either a list of explicit params or a named group. The values for ctx and propq may be NULL. The params that can be used are described in EVP_PKEY-EC(7).

🫶 EC_GROUP_to_params

Creates an OSSL_PARAM array with the corresponding parameters describing the given EC_GROUP. The resulting parameters may contain parameters describing a named or explicit curve depending on the EC_GROUP. The library context libctx (see OSSL_LIB_CTX(3)) and property query string propq are used to fetch algorithms from providers. bnctx is an optional preallocated BN_CTX (to save the overhead of allocating and freeing the structure in a loop). The values for libctx, propq and bnctx may be NULL.

not me being the one to remind you: the caller is responsible for freeing the OSSL_PARAM pointer returned. yes YOU. 🫵

🫶 EC_GROUP_new_from_ecparameters() and EC_GROUP_new_from_ecpkparameters()

EC_GROUP_new_from_ecparameters() will create a group from the specified params, and EC_GROUP_new_from_ecpkparameters() will create a group from the specific PK params. iconic behaviour honestly.

🫶 EC_GROUP_set_curve() and EC_GROUP_get_curve()

EC_GROUP_set_curve() sets the curve parameters p, a and b.

  • 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. So there will either be three or five bits set, depending on whether the polynomial is a trinomial or a pentanomial.

In either case, a and b represent the coefficients a and b from the relevant equation introduced above. 💖

EC_group_get_curve() obtains the previously set curve parameters.

🫶 the deprecated synonym girlies

EC_GROUP_set_curve_GFp() and EC_GROUP_set_curve_GF2m() are synonyms for EC_GROUP_set_curve(). They are defined for backwards compatibility only and should not be used.

EC_GROUP_get_curve_GFp() and EC_GROUP_get_curve_GF2m() are synonyms for EC_GROUP_get_curve(). They are defined for backwards compatibility only and should not be used.

🫶 EC_GROUP_new_curve_GFp() and EC_GROUP_new_curve_GF2m()

These two are shortcuts for calling EC_GROUP_new() and then the EC_GROUP_set_curve() function. An appropriate default implementation method will be used. efficient! 💅

🫶 the predefined curves, aka built-ins

Whilst the library can be used to create any curve using the functions described above, there are also a number of predefined curves that are available. To obtain a list of all of the predefined curves, call EC_get_builtin_curves().

  • The parameter r should be an array of EC_builtin_curve structures of size nitems.
  • The function will populate the r array with information about the built-in curves.
  • If nitems is less than the total number of curves available, then the first nitems curves will be returned. Otherwise the total number of curves will be provided.
  • The return value is the total number of curves available (whether that number has been populated in r or not).
  • Passing a NULL r, or setting nitems to 0, will do nothing other than return the total number of curves available.

The EC_builtin_curve structure is defined as follows:

 typedef struct {
        int nid;
        const char *comment;
        } EC_builtin_curve;

Each EC_builtin_curve item has a unique integer id (nid), and a human readable comment string describing the curve. cute right? 🥰

To construct a built-in curve, use EC_GROUP_new_by_curve_name_ex() and provide:

  • the nid of the curve to be constructed,
  • the associated library context to be used in ctx (see OSSL_LIB_CTX(3)),
  • and any property query string in propq.

The ctx value may be NULL, in which case the default library context is used. The propq value may also be NULL.

EC_GROUP_new_by_curve_name() is the same as EC_GROUP_new_by_curve_name_ex() except that the default library context is always used along with a NULL property query string.

🫶 freeing stuff

EC_GROUP_free() frees the memory associated with the EC_GROUP. If group is NULL nothing is done.

EC_GROUP_clear_free() is deprecated: it was meant to destroy any sensitive data held within the EC_GROUP and then free its memory, but since all the data stored in the EC_GROUP is public anyway, this function is unnecessary. Its use can be safely replaced with EC_GROUP_free(). If group is NULL nothing is done.

🫶 name translation services ✨

OSSL_EC_curve_nid2name() converts a curve nid into the corresponding name.

EC_curve_nid2nist() converts a curve nid into the corresponding NIST name. NIST names are standardized curve names defined by NIST, such as:

  • prime field curves: "P-192", "P-224", "P-256", "P-384", and "P-521"
  • binary field curves: "B-163", "B-233", "B-283", "B-409", "B-571", "K-163", "K-233", "K-283", "K-409", and "K-571"

If the curve specified by nid does not have a NIST name, this function returns NULL.

EC_curve_nist2nid() converts a NIST curve name name to the corresponding NID. The name argument should be a string containing a NIST curve name such as "P-256" or "B-163". If the name does not correspond to a known NIST curve, this function returns NID_undef.

👑 RETURN VALUES 👑

  • All EC_GROUP_new* functions return a pointer to the newly constructed group, or NULL on error.
  • EC_get_builtin_curves() returns the number of built-in curves that are available.
  • EC_GROUP_set_curve_GFp(), EC_GROUP_get_curve_GFp(), EC_GROUP_set_curve_GF2m(), EC_GROUP_get_curve_GF2m() return 1 on success or 0 on error.
  • OSSL_EC_curve_nid2name() returns a character string constant, or NULL on error.
  • EC_curve_nid2nist() returns a pointer to a constant string containing the NIST name for the specified curve, or NULL if the curve does not have a NIST name.
  • EC_curve_nist2nid() returns the NID of the curve with the given NIST name, or NID_undef if the name does not correspond to a known NIST curve.

🌈 SEE ALSO 🌈

crypto(7), EC_GROUP_copy(3), EC_POINT_new(3), EC_POINT_add(3), EC_KEY_new(3), EC_GFp_simple_method(3), d2i_ECPKParameters(3), OSSL_LIB_CTX(3), EVP_PKEY-EC(7)

✨ HISTORY ✨

ok so the timeline bestie, let's get into it 📜:

  • EC_GROUP_to_params() showed up in OpenSSL 3.2. new function, fresh off the block 💅
  • EC_GROUP_new() got deprecated in OpenSSL 3.0. rip to a real one 😭

EC_GROUP_new_by_curve_name_ex() and EC_GROUP_new_from_params() were both added in OpenSSL 3.0 — so like, they're the glow-up replacements, no cap ✨

  • EC_GROUP_clear_free() was deprecated in OpenSSL 3.0; use EC_GROUP_free() instead. okay so stop calling the old one, use the new one, periodt 🫶
  • EC_GROUP_set_curve_GFp(), EC_GROUP_get_curve_GFp(), EC_GROUP_set_curve_GF2m() and EC_GROUP_get_curve_GF2m() were deprecated in OpenSSL 3.0; use EC_GROUP_set_curve() and EC_GROUP_get_curve() instead. the GFp/GF2m era is over, the unified versions ate and left no crumbs 👑
tl;dr for the history girlies: if it says "deprecated in 3.0" that means there is a shiny replacement and you should be using that one instead. don't be the last one still calling the old functions at the group chat 💀

Copyright 2013-2026 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>.

okay that's the whole page bestie, you read the ENTIRE thing, that's main character energy fr fr 🎀✨ this was EC_GROUP_NEW(3SSL) from OpenSSL 4.0.3, dated 2026-09-29 — go forth and make your elliptic curves iconic, ily, bye 💖🦋🌸

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