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Change ecp_mul to handle Curve25519 too

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This commit is contained in:
Manuel Pégourié-Gonnard
2013-12-04 11:49:20 +01:00
parent 312d2e8ea2
commit a0179b8c4a
3 changed files with 98 additions and 27 deletions
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69
library/ecp.c
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@@ -1227,11 +1227,13 @@ cleanup:
}
/*
* Multiplication using the comb method
* Multiplication using the comb method,
* for curves in short Weierstrass form
*/
int ecp_mul( ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
static int ecp_mul_comb( ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
unsigned char w, m_is_odd, p_eq_g, pre_len, i;
@@ -1240,28 +1242,13 @@ int ecp_mul( ecp_group *grp, ecp_point *R,
ecp_point *T;
mpi M, mm;
/*
* Sanity checks (before we even initialize anything)
*/
if( mpi_cmp_int( &P->Z, 1 ) != 0 ||
mpi_get_bit( &grp->N, 0 ) != 1 )
{
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
}
if( ( ret = ecp_check_privkey( grp, m ) ) != 0 )
return( ret );
/* We'll need this later, but do it now to possibly avoid checking P */
p_eq_g = ( mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 &&
mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 );
if( ! p_eq_g && ( ret = ecp_check_pubkey( grp, P ) ) != 0 )
return( ret );
mpi_init( &M );
mpi_init( &mm );
/* we need N to be odd to trnaform m in an odd number, check now */
if( mpi_get_bit( &grp->N, 0 ) != 1 )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
/*
* Minimize the number of multiplications, that is minimize
* 10 * d * w + 18 * 2^(w-1) + 11 * d + 7 * w, with d = ceil( nbits / w )
@@ -1273,6 +1260,8 @@ int ecp_mul( ecp_group *grp, ecp_point *R,
* If P == G, pre-compute a bit more, since this may be re-used later.
* Just adding one ups the cost of the first mul by at most 3%.
*/
p_eq_g = ( mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 &&
mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 );
if( p_eq_g )
w++;
@@ -1466,11 +1455,13 @@ cleanup:
}
/*
* Multiplication with Montgomery ladder in x/z coordinates
* Multiplication with Montgomery ladder in x/z coordinates,
* for curves in Montgomery form
*/
int ecp_mul_mxz( ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
static int ecp_mul_mxz( ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
size_t i;
@@ -1505,6 +1496,30 @@ cleanup:
return( ret );
}
/*
* Multiplication R = m * P
*/
int ecp_mul( ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P,
int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
int ret;
/* Common sanity checks */
if( mpi_cmp_int( &P->Z, 1 ) != 0 )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
if( ( ret = ecp_check_privkey( grp, m ) ) != 0 ||
( ret = ecp_check_pubkey( grp, P ) ) != 0 )
return( ret );
/* Actual multiplication aglorithm depending of curve type */
if( ecp_is_montgomery( grp ) )
return( ecp_mul_mxz( grp, R, m, P, f_rng, p_rng ) );
else
return( ecp_mul_comb( grp, R, m, P, f_rng, p_rng ) );
}
/*
* Check that a point is valid as a public key
*/