Commit 43986596 authored by Dr. Stephen Henson's avatar Dr. Stephen Henson
Browse files

Update and clarify EC_POINT documentation. 



Reformat EC_POINT_new.pod and add parentheses to function names.
Clarify the octet form.
Add documentation for EC_POINT_oct2buf().

Reviewed-by: default avatarRich Salz <rsalz@openssl.org>
parent 766579ec

doc/crypto/EC_POINT_new.pod

+135 −80
Original line number Diff line number Diff line
@@ -2,7 +2,15 @@ 


=head1 NAME



EC_POINT_new, EC_POINT_free, EC_POINT_clear_free, EC_POINT_copy, EC_POINT_dup, EC_POINT_method_of, EC_POINT_set_to_infinity, EC_POINT_set_Jprojective_coordinates, EC_POINT_get_Jprojective_coordinates_GFp, EC_POINT_set_affine_coordinates_GFp, EC_POINT_get_affine_coordinates_GFp, EC_POINT_set_compressed_coordinates_GFp, EC_POINT_set_affine_coordinates_GF2m, EC_POINT_get_affine_coordinates_GF2m, EC_POINT_set_compressed_coordinates_GF2m, EC_POINT_point2oct, EC_POINT_oct2point, EC_POINT_point2bn, EC_POINT_bn2point, EC_POINT_point2hex, EC_POINT_hex2point - Functions for creating, destroying and manipulating B<EC_POINT> objects.

EC_POINT_new, EC_POINT_free, EC_POINT_clear_free, EC_POINT_copy, EC_POINT_dup,

EC_POINT_method_of, EC_POINT_set_to_infinity,

EC_POINT_set_Jprojective_coordinates, EC_POINT_get_Jprojective_coordinates_GFp,

EC_POINT_set_affine_coordinates_GFp, EC_POINT_get_affine_coordinates_GFp,

EC_POINT_set_compressed_coordinates_GFp, EC_POINT_set_affine_coordinates_GF2m,

EC_POINT_get_affine_coordinates_GF2m, EC_POINT_set_compressed_coordinates_GF2m,

EC_POINT_point2oct, EC_POINT_oct2point, EC_POINT_point2bn, EC_POINT_bn2point,

EC_POINT_point2hex, EC_POINT_hex2point - Functions for creating, destroying and

manipulating B<EC_POINT> objects.



=head1 SYNOPSIS
@@ -16,110 +24,157 @@ EC_POINT_new, EC_POINT_free, EC_POINT_clear_free, EC_POINT_copy, EC_POINT_dup, E 
 EC_POINT *EC_POINT_dup(const EC_POINT *src, const EC_GROUP *group);

 const EC_METHOD *EC_POINT_method_of(const EC_POINT *point);

 int EC_POINT_set_to_infinity(const EC_GROUP *group, EC_POINT *point);

 int EC_POINT_set_Jprojective_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,

	const BIGNUM *x, const BIGNUM *y, const BIGNUM *z, BN_CTX *ctx);

 int EC_POINT_set_Jprojective_coordinates_GFp(const EC_GROUP *group,

                                              EC_POINT *p,

                                              const BIGNUM *x, const BIGNUM *y,

                                              const BIGNUM *z, BN_CTX *ctx);

 int EC_POINT_get_Jprojective_coordinates_GFp(const EC_GROUP *group,

	const EC_POINT *p, BIGNUM *x, BIGNUM *y, BIGNUM *z, BN_CTX *ctx);

                                              const EC_POINT *p,

                                              BIGNUM *x, BIGNUM *y, BIGNUM *z,

                                              BN_CTX *ctx);

 int EC_POINT_set_affine_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,

	const BIGNUM *x, const BIGNUM *y, BN_CTX *ctx);

                                         const BIGNUM *x, const BIGNUM *y,

                                         BN_CTX *ctx);

 int EC_POINT_get_affine_coordinates_GFp(const EC_GROUP *group,

	const EC_POINT *p, BIGNUM *x, BIGNUM *y, BN_CTX *ctx);

 int EC_POINT_set_compressed_coordinates_GFp(const EC_GROUP *group, EC_POINT *p,

	const BIGNUM *x, int y_bit, BN_CTX *ctx);

                                         const EC_POINT *p,

                                         BIGNUM *x, BIGNUM *y, BN_CTX *ctx);

 int EC_POINT_set_compressed_coordinates_GFp(const EC_GROUP *group,

                                             EC_POINT *p,

                                             const BIGNUM *x, int y_bit,

                                             BN_CTX *ctx);

 int EC_POINT_set_affine_coordinates_GF2m(const EC_GROUP *group, EC_POINT *p,

	const BIGNUM *x, const BIGNUM *y, BN_CTX *ctx);

                                          const BIGNUM *x, const BIGNUM *y,

                                          BN_CTX *ctx);

 int EC_POINT_get_affine_coordinates_GF2m(const EC_GROUP *group,

	const EC_POINT *p, BIGNUM *x, BIGNUM *y, BN_CTX *ctx);

 int EC_POINT_set_compressed_coordinates_GF2m(const EC_GROUP *group, EC_POINT *p,

	const BIGNUM *x, int y_bit, BN_CTX *ctx);

                                          const EC_POINT *p,

                                          BIGNUM *x, BIGNUM *y, BN_CTX *ctx);

 int EC_POINT_set_compressed_coordinates_GF2m(const EC_GROUP *group,

                                              EC_POINT *p,

                                              const BIGNUM *x, int y_bit,

                                              BN_CTX *ctx);

 size_t EC_POINT_point2oct(const EC_GROUP *group, const EC_POINT *p,

                           point_conversion_form_t form,

                           unsigned char *buf, size_t len, BN_CTX *ctx);

 size_t EC_POINT_point2buf(const EC_GROUP *group, const EC_POINT *point,

                           point_conversion_form_t form,

                           unsigned char **pbuf, BN_CTX *ctx);

 int EC_POINT_oct2point(const EC_GROUP *group, EC_POINT *p,

                        const unsigned char *buf, size_t len, BN_CTX *ctx);

 BIGNUM *EC_POINT_point2bn(const EC_GROUP *, const EC_POINT *,

	point_conversion_form_t form, BIGNUM *, BN_CTX *);

 EC_POINT *EC_POINT_bn2point(const EC_GROUP *, const BIGNUM *,

	EC_POINT *, BN_CTX *);

 char *EC_POINT_point2hex(const EC_GROUP *, const EC_POINT *,

	point_conversion_form_t form, BN_CTX *);

 EC_POINT *EC_POINT_hex2point(const EC_GROUP *, const char *,

	EC_POINT *, BN_CTX *);

 BIGNUM *EC_POINT_point2bn(const EC_GROUP *group, const EC_POINT *p,

                           point_conversion_form_t form, BIGNUM *bn,

                           BN_CTX *ctx);

 EC_POINT *EC_POINT_bn2point(const EC_GROUP *group, const BIGNUM *bn,

                             EC_POINT *p, BN_CTX *ctx);

 char *EC_POINT_point2hex(const EC_GROUP *group, const EC_POINT *p,

                          point_conversion_form_t form, BN_CTX *ctx);

 EC_POINT *EC_POINT_hex2point(const EC_GROUP *group, const char *hex,

                              EC_POINT *p, BN_CTX *ctx);





=head1 DESCRIPTION



An EC_POINT represents a point on a curve. A new point is constructed by calling the function EC_POINT_new and providing the B<group>

object that the point relates to.



EC_POINT_free frees the memory associated with the EC_POINT.

if B<point> is NULL nothing is done.

An B<EC_POINT> structure represents a point on a curve. A new point is

constructed by calling the function EC_POINT_new() and providing the

B<group> object that the point relates to.



EC_POINT_clear_free destroys any sensitive data held within the EC_POINT and then frees its memory.

EC_POINT_free() frees the memory associated with the B<EC_POINT>.

if B<point> is NULL nothing is done.



EC_POINT_copy copies the point B<src> into B<dst>. Both B<src> and B<dst> must use the same EC_METHOD.



EC_POINT_dup creates a new EC_POINT object and copies the content from B<src> to the newly created

EC_POINT object.



EC_POINT_method_of obtains the EC_METHOD associated with B<point>.



A valid point on a curve is the special point at  infinity. A point is set to be at infinity by calling EC_POINT_set_to_infinity.



The affine co-ordinates for a point describe a point in terms of its x and y position. The functions

EC_POINT_set_affine_coordinates_GFp and EC_POINT_set_affine_coordinates_GF2m set the B<x> and B<y> co-ordinates for the point

B<p> defined over the curve given in B<group>.



As well as the affine co-ordinates, a point can alternatively be described in terms of its Jacobian

projective co-ordinates (for Fp curves only). Jacobian projective co-ordinates are expressed as three values x, y and z. Working in

this co-ordinate system provides more efficient point multiplication operations.

A mapping exists between Jacobian projective co-ordinates and affine co-ordinates. A Jacobian projective co-ordinate (x, y, z) can be written as an affine co-ordinate as (x/(z^2), y/(z^3)). Conversion to Jacobian projective to affine co-ordinates is simple. The co-ordinate (x, y) is

mapped to (x, y, 1). To set or get the projective co-ordinates use EC_POINT_set_Jprojective_coordinates_GFp and

EC_POINT_get_Jprojective_coordinates_GFp respectively.



Points can also be described in terms of their compressed co-ordinates. For a point (x, y), for any given value for x such that the point is

on the curve there will only ever be two possible values for y. Therefore a point can be set using the EC_POINT_set_compressed_coordinates_GFp

and EC_POINT_set_compressed_coordinates_GF2m functions where B<x> is the x co-ordinate and B<y_bit> is a value 0 or 1 to identify which of

the two possible values for y should be used.



In addition EC_POINTs can be converted to and from various external

representations. Supported representations are octet strings, BIGNUMs and

hexadecimal. Octet strings are stored in a buffer along with an associated

buffer length. A point held in a BIGNUM is calculated by converting the point to

an octet string and then converting that octet string into a BIGNUM integer.

Points in hexadecimal format are stored in a NULL terminated character string

where each character is one of the printable values 0-9 or A-F (or a-f).



The functions EC_POINT_point2oct, EC_POINT_oct2point, EC_POINT_point2bn, EC_POINT_bn2point, EC_POINT_point2hex and EC_POINT_hex2point convert

from and to EC_POINTs for the formats: octet string, BIGNUM and hexadecimal respectively.



The function EC_POINT_point2oct must be supplied with a buffer long enough to store the octet string. The return value provides the number of

octets stored. Calling the function with a NULL buffer will not perform the conversion but will still return the required buffer length.



The function EC_POINT_point2hex will allocate sufficient memory to store the hexadecimal string. It is the caller's responsibility to free

this memory with a subsequent call to OPENSSL_free().

EC_POINT_clear_free() destroys any sensitive data held within the EC_POINT and

then frees its memory. If B<point> is NULL nothing is done.



EC_POINT_copy() copies the point B<src> into B<dst>. Both B<src> and B<dst>

must use the same B<EC_METHOD>.



EC_POINT_dup() creates a new B<EC_POINT> object and copies the content from

B<src> to the newly created B<EC_POINT> object.



EC_POINT_method_of() obtains the B<EC_METHOD> associated with B<point>.



A valid point on a curve is the special point at infinity. A point is set to

be at infinity by calling EC_POINT_set_to_infinity().



The affine co-ordinates for a point describe a point in terms of its x and y

position. The functions EC_POINT_set_affine_coordinates_GFp() and

EC_POINT_set_affine_coordinates_GF2m() set the B<x> and B<y> co-ordinates for

the point B<p> defined over the curve given in B<group>.



As well as the affine co-ordinates, a point can alternatively be described in

terms of its Jacobian projective co-ordinates (for Fp curves only). Jacobian

projective co-ordinates are expressed as three values x, y and z. Working in

this co-ordinate system provides more efficient point multiplication

operations.  A mapping exists between Jacobian projective co-ordinates and

affine co-ordinates. A Jacobian projective co-ordinate (x, y, z) can be written

as an affine co-ordinate as (x/(z^2), y/(z^3)). Conversion to Jacobian

projective to affine co-ordinates is simple. The co-ordinate (x, y) is mapped

to (x, y, 1). To set or get the projective co-ordinates use

EC_POINT_set_Jprojective_coordinates_GFp() and

EC_POINT_get_Jprojective_coordinates_GFp() respectively.



Points can also be described in terms of their compressed co-ordinates. For a

point (x, y), for any given value for x such that the point is on the curve

there will only ever be two possible values for y. Therefore a point can be set

using the EC_POINT_set_compressed_coordinates_GFp() and

EC_POINT_set_compressed_coordinates_GF2m() functions where B<x> is the x

co-ordinate and B<y_bit> is a value 0 or 1 to identify which of the two

possible values for y should be used.



In addition B<EC_POINT> can be converted to and from various external

representations. The octet form is the binary encoding of the B<ECPoint>

structure (as defined in RFC5480 and used in certificates and TLS records):

only the content octets are present, the B<OCTET STRING> tag and length are

not included. B<BIGNUM> form is the octet form interpreted as a big endian

integer converted to a B<BIGNUM> structure. Hexadecimal form is the octet

form converted to a NULL terminated character string where each character

is one of the printable values 0-9 or A-F (or a-f).



The functions EC_POINT_point2oct(), EC_POINT_oct2point(), EC_POINT_point2bn(),

EC_POINT_bn2point(), EC_POINT_point2hex() and EC_POINT_hex2point() convert from

and to EC_POINTs for the formats: octet, BIGNUM and hexadecimal respectively.



The function EC_POINT_point2oct() must be supplied with a buffer long enough to

store the octet form. The return value provides the number of octets stored.

Calling the function with a NULL buffer will not perform the conversion but

will still return the required buffer length.



The function EC_POINT_point2buf() allocates a buffer of suitable length and

writes an EC_POINT to it in octet format. The allocated buffer is written to

B<*pbuf> and its length is returned. The caller must free up the allocated

buffer with a call to OPENSSL_free(). Since the allocated buffer value is

written to B<*pbuf> the B<pbuf> parameter B<MUST NOT> be B<NULL>.



The function EC_POINT_point2hex() will allocate sufficient memory to store the

hexadecimal string. It is the caller's responsibility to free this memory with

a subsequent call to OPENSSL_free().



=head1 RETURN VALUES



EC_POINT_new and EC_POINT_dup return the newly allocated EC_POINT or NULL on error.

EC_POINT_new() and EC_POINT_dup() return the newly allocated EC_POINT or NULL

on error.



The following functions return 1 on success or 0 on error: EC_POINT_copy, EC_POINT_set_to_infinity, EC_POINT_set_Jprojective_coordinates_GFp,

EC_POINT_get_Jprojective_coordinates_GFp, EC_POINT_set_affine_coordinates_GFp, EC_POINT_get_affine_coordinates_GFp,

EC_POINT_set_compressed_coordinates_GFp, EC_POINT_set_affine_coordinates_GF2m, EC_POINT_get_affine_coordinates_GF2m,

EC_POINT_set_compressed_coordinates_GF2m and EC_POINT_oct2point.

The following functions return 1 on success or 0 on error: EC_POINT_copy(),

EC_POINT_set_to_infinity(), EC_POINT_set_Jprojective_coordinates_GFp(),

EC_POINT_get_Jprojective_coordinates_GFp(),

EC_POINT_set_affine_coordinates_GFp(), EC_POINT_get_affine_coordinates_GFp(),

EC_POINT_set_compressed_coordinates_GFp(),

EC_POINT_set_affine_coordinates_GF2m(), EC_POINT_get_affine_coordinates_GF2m(),

EC_POINT_set_compressed_coordinates_GF2m() and EC_POINT_oct2point().



EC_POINT_method_of returns the EC_METHOD associated with the supplied EC_POINT.



EC_POINT_point2oct returns the length of the required buffer, or 0 on error.

EC_POINT_point2oct() and EC_point2buf() return the length of the required

buffer or 0 on error.



EC_POINT_point2bn returns the pointer to the BIGNUM supplied, or NULL on error.

EC_POINT_point2bn() returns the pointer to the BIGNUM supplied, or NULL on

error.



EC_POINT_bn2point returns the pointer to the EC_POINT supplied, or NULL on error.

EC_POINT_bn2point() returns the pointer to the EC_POINT supplied, or NULL on

error.



EC_POINT_point2hex returns a pointer to the hex string, or NULL on error.

EC_POINT_point2hex() returns a pointer to the hex string, or NULL on error.



EC_POINT_hex2point returns the pointer to the EC_POINT supplied, or NULL on error.

EC_POINT_hex2point() returns the pointer to the EC_POINT supplied, or NULL on

error.



=head1 SEE ALSO