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EC_GFp_nistp256_method.3
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When constructing a curve using EC_GROUP_new (see \fIEC_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 \fIBN_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 \fIEC_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\s0 P224, P256 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" \&\fIcrypto\fR\|(3), \fIec\fR\|(3), \fIEC_GROUP_new\fR\|(3), \fIEC_GROUP_copy\fR\|(3), \&\fIEC_POINT_new\fR\|(3), \fIEC_POINT_add\fR\|(3), \fIEC_KEY_new\fR\|(3), \&\fId2i_ECPKParameters\fR\|(3), \&\fIBN_mod_mul_montgomery\fR\|(3)