- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- SEE ALSO
- COPYRIGHT

# 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 - Functions for obtaining 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. When constructing a curve using EC_GROUP_new (see 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. 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, i.e. 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 builds on EC_GFp_simple_method but 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 as described in EC_GROUP_new(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 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

crypto(7), EC_GROUP_new(3), EC_GROUP_copy(3), EC_POINT_new(3), EC_POINT_add(3), EC_KEY_new(3), d2i_ECPKParameters(3), BN_mod_mul_montgomery(3)

# COPYRIGHT

Copyright 2013-2017 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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.