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.IX Title "EC_GFp_simple_method 3"
.TH EC_GFp_simple_method 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.SH "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.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "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 \fBEC_GROUP_new\fR\|(3)) an
implementation method must be provided. The functions described here all return a const pointer to an
\&\fB\s-1EC_METHOD\s0\fR structure that can be passed to \s-1EC_GROUP_NEW.\s0 It is important that the correct implementation
type for the form of curve selected is used.
.PP
For F2^m curves there is only one implementation choice, i.e. EC_GF2_simple_method.
.PP
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 \fBBN_mod_mul_montgomery\fR\|(3)). EC_GFp_nist_method
offers an implementation optimised for use with \s-1NIST\s0 recommended curves (\s-1NIST\s0 curves are available through
EC_GROUP_new_by_curve_name as described in \fBEC_GROUP_new\fR\|(3)).
.PP
The functions EC_GFp_nistp224_method, EC_GFp_nistp256_method and EC_GFp_nistp521_method offer 64 bit
optimised implementations for the \s-1NIST P224, P256\s0 and P521 curves respectively. Note, however, that these
implementations are not available on all platforms.
.PP
EC_METHOD_get_field_type identifies what type of field the \s-1EC_METHOD\s0 structure supports, which will be either
F2^m or Fp. If the field type is Fp then the value \fBNID_X9_62_prime_field\fR is returned. If the field type is
F2^m then the value \fBNID_X9_62_characteristic_two_field\fR is returned. These values are defined in the
obj_mac.h header file.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
All EC_GFp* functions and EC_GF2m_simple_method always return a const pointer to an \s-1EC_METHOD\s0 structure.
.PP
EC_METHOD_get_field_type returns an integer that identifies the type of field the \s-1EC_METHOD\s0 structure supports.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBcrypto\fR\|(3), \fBec\fR\|(3), \fBEC_GROUP_new\fR\|(3), \fBEC_GROUP_copy\fR\|(3),
\&\fBEC_POINT_new\fR\|(3), \fBEC_POINT_add\fR\|(3), \fBEC_KEY_new\fR\|(3),
\&\fBd2i_ECPKParameters\fR\|(3),
\&\fBBN_mod_mul_montgomery\fR\|(3)
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