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Got started on ecp_add(): generic case done

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Manuel Pégourié-Gonnard 2012-11-02 18:14:40 +01:00 committed by Paul Bakker
parent 883f313516
commit ae180d0f20
2 changed files with 144 additions and 1 deletions
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12
include/polarssl/ecp.h
View File

@ -36,6 +36,8 @@
/**
* \brief ECP point structure (affine coordinates)
*
* Note: if the point is zero, X and Y are irrelevant and should be freed.
*/
typedef struct
{
@ -145,6 +147,11 @@ ecp_group;
extern "C" {
#endif
/**
* \brief Initialize a point
*/
void ecp_point_init( ecp_point *pt );
/**
* \brief Free the components of a point
*/
@ -155,6 +162,11 @@ void ecp_point_free( ecp_point *pt );
*/
void ecp_group_free( ecp_group *grp );
/**
* \brief Set a point to zero
*/
void ecp_set_zero( ecp_point *pt );
/**
* \brief Copy the contents of point Q into P
*

133
library/ecp.c
View File

@ -36,6 +36,19 @@
#include "polarssl/ecp.h"
/*
* Initialize a point
*/
void ecp_point_init( ecp_point *pt )
{
if( pt == NULL )
return;
pt->is_zero = 1;
mpi_init( &( pt->X ) );
mpi_init( &( pt->Y ) );
}
/*
* Unallocate (the components of) a point
*/
@ -63,12 +76,22 @@ void ecp_group_free( ecp_group *grp )
mpi_free( &grp->N );
}
/*
* Set point to zero
*/
void ecp_set_zero( ecp_point *pt )
{
pt->is_zero = 1;
mpi_free( &( pt->X ) );
mpi_free( &( pt->Y ) );
}
/*
* Copy the contents of Q into P
*/
int ecp_copy( ecp_point *P, const ecp_point *Q )
{
int ret;
int ret = 0;
P->is_zero = Q->is_zero;
MPI_CHK( mpi_copy( &P->X, &Q->X ) );
@ -78,6 +101,114 @@ cleanup:
return( ret );
}
/*
* Addition: R = P + Q, generic case (P != Q, P != 0, Q != 0, R != 0)
* Cf SEC1 v2 p. 7, item 4
*/
static int ecp_add_generic( const ecp_group *grp, ecp_point *R,
const ecp_point *P, const ecp_point *Q )
{
int ret = 0;
mpi DX, DY, K, L, LL, M, X, Y;
mpi_init( &DX ); mpi_init( &DY ); mpi_init( &K ); mpi_init( &L );
mpi_init( &LL ); mpi_init( &M ); mpi_init( &X ); mpi_init( &Y );
/*
* L = (Q.Y - P.Y) / (Q.X - P.X) mod p
*/
MPI_CHK( mpi_sub_mpi( &DY, &Q->Y, &P->Y ) );
MPI_CHK( mpi_sub_mpi( &DX, &Q->X, &P->X ) );
MPI_CHK( mpi_inv_mod( &K, &DX, &grp->P ) );
MPI_CHK( mpi_mul_mpi( &K, &K, &DY ) );
MPI_CHK( mpi_mod_mpi( &L, &K, &grp->P ) );
/*
* LL = L^2 mod p
* M = L^2 - Q.X
* X = L^2 - P.X - Q.X
*/
MPI_CHK( mpi_mul_mpi( &LL, &L, &L ) );
MPI_CHK( mpi_mod_mpi( &LL, &LL, &grp->P ) );
MPI_CHK( mpi_sub_mpi( &M, &LL, &Q->X ) );
MPI_CHK( mpi_sub_mpi( &X, &M, &P->X ) );
/*
* Y = L * (P.X - X) - P.Y = L * (-M) - P.Y
*/
MPI_CHK( mpi_copy( &Y, &M ) );
Y.s = - Y.s;
MPI_CHK( mpi_mul_mpi( &Y, &Y, &L ) );
MPI_CHK( mpi_sub_mpi( &Y, &Y, &P->Y ) );
/*
* R = (X mod p, Y mod p)
*/
R->is_zero = 0;
MPI_CHK( mpi_mod_mpi( &R->X, &X, &grp->P ) );
MPI_CHK( mpi_mod_mpi( &R->Y, &Y, &grp->P ) );
cleanup:
mpi_free( &DX ); mpi_free( &DY ); mpi_free( &K ); mpi_free( &L );
mpi_free( &LL ); mpi_free( &M ); mpi_free( &X ); mpi_free( &Y );
return( ret );
}
/*
* Doubling: R = 2 * P, generic case (P != 0, R != 0)
*
* Returns POLARSSL_ERR_MPI_XXX on error.
*/
static int ecp_double_generic( const ecp_group *grp, ecp_point *R,
const ecp_point *P )
{
int ret = 0;
(void) grp;
(void) R;
(void) P;
return( ret );
}
/*
* Addition: R = P + Q, cf p. 7 of SEC1 v2
*/
int ecp_add( const ecp_group *grp, ecp_point *R,
const ecp_point *P, const ecp_point *Q )
{
int ret = 0;
if( P->is_zero )
{
ret = ecp_copy( R, Q );
}
else if( Q->is_zero )
{
ret = ecp_copy( R, P );
}
else if( mpi_cmp_mpi( &P->X, &Q->X ) != 0 )
{
ret = ecp_add_generic( grp, R, P, Q );
}
else if( mpi_cmp_int( &P->Y, 0 ) == 0 ||
mpi_cmp_mpi( &P->Y, &Q->Y ) != 0 )
{
ecp_set_zero( R );
}
else
{
/*
* P == Q
*/
ret = ecp_double_generic( grp, R, P );
}
return ret;
}
#if defined(POLARSSL_SELF_TEST)