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Tune T ownership code + comments

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Don't miss the little code changes among all those comments change :)
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Manuel Pégourié-Gonnard 2017-03-16 17:21:38 +01:00
parent 085b1dff40
commit 07bf6f52c1
1 changed files with 27 additions and 7 deletions
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34
library/ecp.c
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@ -1618,8 +1618,17 @@ static unsigned char ecp_pick_window_size( const mbedtls_ecp_group *grp,
} }
/* /*
* Multiplication using the comb method, * Multiplication using the comb method - for curves in short Weierstrass form
* for curves in short Weierstrass form *
* This function is mainly responsible for administrative work:
* - managing the restart context if enabled
* - managing the table of precomputed points (passed between the above two
* functions): allocation, computation, ownership tranfer, freeing.
*
* It delegates the actual arithmetic work to:
* ecp_precompute_comb() and ecp_mul_comb_with_precomp()
*
* See comments on ecp_comb_recode_core() regarding the computation strategy.
*/ */
static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R, static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
const mbedtls_mpi *m, const mbedtls_ecp_point *P, const mbedtls_mpi *m, const mbedtls_ecp_point *P,
@ -1657,7 +1666,7 @@ static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
MBEDTLS_MPI_CHK( mbedtls_ecp_copy( &grp->rs->P, P ) ); MBEDTLS_MPI_CHK( mbedtls_ecp_copy( &grp->rs->P, P ) );
} }
/* new start for ops counts */ /* reset ops count for this call */
if( grp->rs != NULL ) if( grp->rs != NULL )
grp->rs->ops_done = 0; grp->rs->ops_done = 0;
#endif #endif
@ -1676,6 +1685,8 @@ static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
/* Pre-computed table: do we have it already for the base point? */ /* Pre-computed table: do we have it already for the base point? */
if( p_eq_g && grp->T != NULL ) if( p_eq_g && grp->T != NULL )
{ {
/* second pointer to the same table
* no ownership transfer as other threads might be using T too */
T = grp->T; T = grp->T;
T_ok = 1; T_ok = 1;
} }
@ -1684,7 +1695,7 @@ static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
/* Pre-computed table: do we have one in progress? complete? */ /* Pre-computed table: do we have one in progress? complete? */
if( grp->rs != NULL && grp->rs->T != NULL && T == NULL ) if( grp->rs != NULL && grp->rs->T != NULL && T == NULL )
{ {
/* transfer "ownership" of T from rs to local function */ /* transfer ownership of T from rs to local function */
T = grp->rs->T; T = grp->rs->T;
grp->rs->T = NULL; grp->rs->T = NULL;
grp->rs->T_size = 0; grp->rs->T_size = 0;
@ -1714,6 +1725,7 @@ static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
{ {
grp->T = T; grp->T = T;
grp->T_size = pre_len; grp->T_size = pre_len;
/* now have two pointers to the same table */
} }
} }
@ -1724,17 +1736,23 @@ static int ecp_mul_comb( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
cleanup: cleanup:
/* does T belong to the group? */
if( T == grp->T )
T = NULL;
/* does T belong to the restart context? */
#if defined(MBEDTLS_ECP_EARLY_RETURN) #if defined(MBEDTLS_ECP_EARLY_RETURN)
if( grp->rs != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS && T != grp->T ) if( grp->rs != NULL && ret == MBEDTLS_ERR_ECP_IN_PROGRESS && T != NULL )
{ {
/* transfer "ownership" of T from local function to rs */ /* transfer ownership of T from local function to rs */
grp->rs->T_size = pre_len; grp->rs->T_size = pre_len;
grp->rs->T = T; grp->rs->T = T;
T = NULL; T = NULL;
} }
#endif #endif
if( T != NULL && ! p_eq_g ) /* did T belong to us? then let's destroy it! */
if( T != NULL )
{ {
for( i = 0; i < pre_len; i++ ) for( i = 0; i < pre_len; i++ )
mbedtls_ecp_point_free( &T[i] ); mbedtls_ecp_point_free( &T[i] );
@ -1745,9 +1763,11 @@ cleanup:
#if defined(MBEDTLS_ECP_EARLY_RETURN) #if defined(MBEDTLS_ECP_EARLY_RETURN)
if( ret != MBEDTLS_ERR_ECP_IN_PROGRESS ) if( ret != MBEDTLS_ERR_ECP_IN_PROGRESS )
#endif #endif
/* prevent caller from using invalid value */
if( ret != 0 ) if( ret != 0 )
mbedtls_ecp_point_free( R ); mbedtls_ecp_point_free( R );
/* clear restart context when not in progress (done or error) */
#if defined(MBEDTLS_ECP_EARLY_RETURN) #if defined(MBEDTLS_ECP_EARLY_RETURN)
if( grp->rs != NULL && ret != MBEDTLS_ERR_ECP_IN_PROGRESS ) { if( grp->rs != NULL && ret != MBEDTLS_ERR_ECP_IN_PROGRESS ) {
ecp_restart_free( grp->rs ); ecp_restart_free( grp->rs );