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NAME

EC_GFp_simple_method, EC_GFp_mont_method, EC_GFp_nist_method, EC_GFp_nistp224_method, EC_GFp_nistp256_method, EC_GFp_nistp521_method, EC_GF2m_simple_method, EC_METHOD_get_field_type — obtain EC_METHOD objects

SYNOPSIS

#include <openssl/ec.h>

const EC_METHOD *
EC_GFp_simple_method(void);

const EC_METHOD *
EC_GFp_mont_method(void);

const EC_METHOD *
EC_GFp_nist_method(void);

const EC_METHOD *
EC_GFp_nistp224_method(void);

const EC_METHOD *
EC_GFp_nistp256_method(void);

const EC_METHOD *
EC_GFp_nistp521_method(void);

const EC_METHOD *
EC_GF2m_simple_method(void);

int
EC_METHOD_get_field_type(const EC_METHOD *meth);

DESCRIPTION

The elliptic curve library provides a number of different implementations through a single common interface. Each implementation is optimised for different scenarios. An implementation is represented by an EC_METHOD structure.

When constructing a curve using EC_GROUP_new(3), an implementation method must be provided. The functions described here all return a const pointer to an EC_METHOD structure that can be passed to EC_GROUP_new(3). It is important that the correct implementation type for the form of curve selected is used.

For F2^m curves there is only one implementation choice, EC_GF2_simple_method().

For Fp curves the lowest common denominator implementation is the EC_GFp_simple_method() implementation. All other implementations are based on this one. EC_GFp_mont_method() adds the use of Montgomery multiplication (see BN_mod_mul_montgomery(3)). EC_GFp_nist_method() offers an implementation optimised for use with NIST recommended curves. NIST curves are available through EC_GROUP_new_by_curve_name(3).

The functions EC_GFp_nistp224_method(), EC_GFp_nistp256_method(), and EC_GFp_nistp521_method() offer 64-bit optimised implementations for the NIST P224, P256 and P521 curves respectively. Note, however, that these implementations are not available on all platforms.

EC_METHOD_get_field_type() identifies what type of field the EC_METHOD structure supports, which will be either F2^m or Fp. If the field type is Fp, then the value NID_X9_62_prime_field is returned. If the field type is F2^m, then the value NID_X9_62_characteristic_two_field is returned. These values are defined in the <openssl/obj_mac.h> header file.

RETURN VALUES

All EC_GFp*() functions and EC_GF2m_simple_method() always return a const pointer to an EC_METHOD structure.

EC_METHOD_get_field_type() returns an integer that identifies the type of field the EC_METHOD structure supports.

SEE ALSO

BN_mod_mul_montgomery(3), d2i_ECPKParameters(3), EC_GROUP_copy(3), EC_GROUP_new(3), EC_KEY_new(3), EC_POINT_add(3), EC_POINT_new(3)

HISTORY

EC_GFp_simple_method() and EC_GFp_mont_method() first appeared in OpenSSL 0.9.7 and have been available since OpenBSD 3.2.

EC_GFp_nist_method(), EC_GF2m_simple_method(), and EC_METHOD_get_field_type() first appeared in OpenSSL 0.9.8 and have been available since OpenBSD 4.5.

EC_GFp_nistp224_method(), EC_GFp_nistp256_method(), and EC_GFp_nistp521_method() first appeared in OpenSSL 1.0.1 and have been available since OpenBSD 5.3.