First version of ecp_mul_comb()
This commit is contained in:
Manuel Pégourié-Gonnard
parent
d1bac4ae55
commit
d1c1ba90ca
@ -476,10 +476,14 @@ int ecp_sub( const ecp_group *grp, ecp_point *R,
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* has very low overhead, it is recommended to always provide
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* a non-NULL f_rng parameter when using secret inputs.
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*/
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int ecp_mul( ecp_group *grp, ecp_point *R,
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const mpi *m, const ecp_point *P,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
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// Temporary, WIP
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int ecp_mul_wnaf( ecp_group *grp, ecp_point *R,
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const mpi *m, const ecp_point *P,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
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int ecp_mul_comb( ecp_group *grp, ecp_point *R,
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const mpi *m, const ecp_point *P,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng );
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#define ecp_mul ecp_mul_comb
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/**
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* \brief Check that a point is a valid public key on this curve
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312
library/ecp.c
312
library/ecp.c
@ -41,6 +41,11 @@
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* for elliptic curve cryptosystems. In : Cryptographic Hardware and
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* Embedded Systems. Springer Berlin Heidelberg, 1999. p. 292-302.
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* <http://link.springer.com/chapter/10.1007/3-540-48059-5_25>
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*
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* [3] HEDABOU, Mustapha, PINEL, Pierre, et BÉNÉTEAU, Lucien. A comb method to
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* render ECC resistant against Side Channel Attacks. IACR Cryptology
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* ePrint Archive, 2004, vol. 2004, p. 342.
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* <http://eprint.iacr.org/2004/342.pdf>
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*/
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#include "polarssl/config.h"
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@ -902,7 +907,7 @@ cleanup:
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}
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/*
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* Normalize jacobian coordinates of an array of points,
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* Normalize jacobian coordinates of an array of (pointers to) points,
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* using Montgomery's trick to perform only one inversion mod P.
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* (See for example Cohen's "A Course in Computational Algebraic Number
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* Theory", Algorithm 10.3.4.)
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@ -911,14 +916,14 @@ cleanup:
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* This should never happen, see choice of w in ecp_mul().
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*/
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static int ecp_normalize_many( const ecp_group *grp,
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ecp_point T[], size_t t_len )
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ecp_point *T[], size_t t_len )
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{
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int ret;
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size_t i;
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mpi *c, u, Zi, ZZi;
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if( t_len < 2 )
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return( ecp_normalize( grp, T ) );
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return( ecp_normalize( grp, *T ) );
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if( ( c = (mpi *) polarssl_malloc( t_len * sizeof( mpi ) ) ) == NULL )
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return( POLARSSL_ERR_ECP_MALLOC_FAILED );
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@ -930,10 +935,10 @@ static int ecp_normalize_many( const ecp_group *grp,
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/*
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* c[i] = Z_0 * ... * Z_i
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*/
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MPI_CHK( mpi_copy( &c[0], &T[0].Z ) );
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MPI_CHK( mpi_copy( &c[0], &T[0]->Z ) );
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for( i = 1; i < t_len; i++ )
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{
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MPI_CHK( mpi_mul_mpi( &c[i], &c[i-1], &T[i].Z ) );
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MPI_CHK( mpi_mul_mpi( &c[i], &c[i-1], &T[i]->Z ) );
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MOD_MUL( c[i] );
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}
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@ -953,18 +958,18 @@ static int ecp_normalize_many( const ecp_group *grp,
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}
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else
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{
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MPI_CHK( mpi_mul_mpi( &Zi, &u, &c[i-1] ) ); MOD_MUL( Zi );
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MPI_CHK( mpi_mul_mpi( &u, &u, &T[i].Z ) ); MOD_MUL( u );
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MPI_CHK( mpi_mul_mpi( &Zi, &u, &c[i-1] ) ); MOD_MUL( Zi );
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MPI_CHK( mpi_mul_mpi( &u, &u, &T[i]->Z ) ); MOD_MUL( u );
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}
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/*
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* proceed as in normalize()
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*/
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MPI_CHK( mpi_mul_mpi( &ZZi, &Zi, &Zi ) ); MOD_MUL( ZZi );
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MPI_CHK( mpi_mul_mpi( &T[i].X, &T[i].X, &ZZi ) ); MOD_MUL( T[i].X );
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MPI_CHK( mpi_mul_mpi( &T[i].Y, &T[i].Y, &ZZi ) ); MOD_MUL( T[i].Y );
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MPI_CHK( mpi_mul_mpi( &T[i].Y, &T[i].Y, &Zi ) ); MOD_MUL( T[i].Y );
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MPI_CHK( mpi_lset( &T[i].Z, 1 ) );
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MPI_CHK( mpi_mul_mpi( &ZZi, &Zi, &Zi ) ); MOD_MUL( ZZi );
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MPI_CHK( mpi_mul_mpi( &T[i]->X, &T[i]->X, &ZZi ) ); MOD_MUL( T[i]->X );
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MPI_CHK( mpi_mul_mpi( &T[i]->Y, &T[i]->Y, &ZZi ) ); MOD_MUL( T[i]->Y );
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MPI_CHK( mpi_mul_mpi( &T[i]->Y, &T[i]->Y, &Zi ) ); MOD_MUL( T[i]->Y );
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MPI_CHK( mpi_lset( &T[i]->Z, 1 ) );
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if( i == 0 )
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break;
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@ -1250,6 +1255,7 @@ static int ecp_precompute( const ecp_group *grp,
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int ret;
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size_t i;
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ecp_point PP;
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ecp_point *TT[ 1 << ( POLARSSL_ECP_WINDOW_SIZE - 1 ) ];
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ecp_point_init( &PP );
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@ -1261,9 +1267,11 @@ static int ecp_precompute( const ecp_group *grp,
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MPI_CHK( ecp_add_mixed( grp, &T[i], &T[i-1], &PP, +1 ) );
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/*
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* T[0] = P already has normalized coordinates
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* T[0] = P already has normalized coordinates, normalize others
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*/
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MPI_CHK( ecp_normalize_many( grp, T + 1, t_len - 1 ) );
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for( i = 1; i < t_len; i++ )
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TT[i-1] = &T[i];
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MPI_CHK( ecp_normalize_many( grp, TT, t_len - 1 ) );
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cleanup:
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@ -1342,9 +1350,9 @@ cleanup:
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* countermeasure against DPA in 5.3 of [2] (with the obvious adaptation that
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* we use jacobian coordinates, not standard projective coordinates).
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*/
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int ecp_mul( ecp_group *grp, ecp_point *R,
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const mpi *m, const ecp_point *P,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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int ecp_mul_wnaf( ecp_group *grp, ecp_point *R,
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const mpi *m, const ecp_point *P,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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{
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int ret;
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unsigned char w, m_is_odd, p_eq_g;
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@ -1503,6 +1511,276 @@ cleanup:
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return( ret );
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}
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/*
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* Compute the representation of m that will be used with the comb method.
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*
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* The basic comb method is described in GECC 3.44 for example. We use a
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* modified version [3] that provides resistance to SPA by avoiding zero
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* digits in the representation. We represent (K_i, s_i) from the paper as a
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* single signed char.
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*
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* Calling conventions:
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* - x is an array of size d
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* - w is the size, ie number of teeth, of the comb
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* - m is the MPI, expected to be odd and such that, if l = bitlength(m):
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* ceil( l / w ) <= d (these two assumptions are not checked, an incorrect
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* result my be returned if they are not satisfied)
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*/
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static void ecp_comb_fixed( signed char x[], size_t d,
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unsigned char w, const mpi *m )
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{
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size_t i, j;
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memset( x, 0, d );
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/* For x[0] use the classical comb value without adjustement */
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for( j = 0; j < w; j++ )
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x[0] |= mpi_get_bit( m, d * j ) << j;
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for( i = 1; i < d; i++ )
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{
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/* Get the classical comb value */
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for( j = 0; j < w; j++ )
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x[i] |= mpi_get_bit( m, i + d * j ) << j;
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/* Adjust if it's zero */
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if( x[i] == 0 )
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{
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x[i] = x[i-1];
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x[i-1] *= -1;
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}
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}
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}
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/*
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* Precompute points for the comb method
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*
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* If i = i_{w-1} ... i_0 is the binary representation of i, then
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* T[i-1] = i_{w-1} 2^{(w-1)d} P + ... + i_1 2^d P + i_0 P
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*
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* T must be able to hold at least 2^w - 1 elements
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*/
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static int ecp_precompute_comb( const ecp_group *grp,
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ecp_point T[], const ecp_point *P,
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unsigned char w, size_t d )
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{
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int ret;
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unsigned char i, mask;
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size_t j, t_len = ( 1U << w ) - 1;
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ecp_point *cur, *TT[t_len - 1];
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/*
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* Compute the 2^{di}
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*/
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MPI_CHK( ecp_copy( &T[0], P ) );
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for( i = 1; i < w; i++ )
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{
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cur = T + ( 1 << i ) - 1;
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ecp_copy( cur, T + ( 1 << (i-1) ) - 1 );
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for( j = 0; j < d; j++ )
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MPI_CHK( ecp_double_jac( grp, cur, cur ) );
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TT[i-1] = cur;
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}
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/* P already normalized, so w - 1 points to do */
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ecp_normalize_many( grp, TT, w - 1);
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/*
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* Compute the remaining ones using the minimal number of additions
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*/
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j = 0;
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for( i = 3; i < (1U << w); i++ )
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{
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if( T[i - 1].X.p != NULL )
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continue;
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/* Find the least significant non-zero bit of the index */
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for( mask = 1; mask != 0; mask <<=1 )
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if( ( i & mask ) != 0 )
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break;
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/* Use the previously computed values */
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ecp_add_mixed( grp, &T[i - 1], &T[i - mask - 1], &T[mask - 1], +1 );
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/* Register for normalisation */
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TT[j++] = &T[i - 1];
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}
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ecp_normalize_many( grp, TT, j );
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cleanup:
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return( ret );
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}
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/*
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* Select precomputed point: R = sign(i) * T[ abs(i) ]
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*/
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static int ecp_select_comb( const ecp_group *grp, ecp_point *R,
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const ecp_point T[], signed char i )
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{
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int ret;
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if( i > 0 )
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return( ecp_copy( R, &T[i - 1] ) );
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MPI_CHK( ecp_copy( R, &T[-i - 1] ) );
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/*
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* -R = (R.X, -R.Y, R.Z), and
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* -R.Y mod P = P - R.Y unless R.Y == 0
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*/
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if( mpi_cmp_int( &R->Y, 0 ) != 0 )
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MPI_CHK( mpi_sub_mpi( &R->Y, &grp->P, &R->Y ) );
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cleanup:
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return( ret );
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}
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/*
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* Core multiplication algorithm for the (modified) comb method.
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* This part is actually common with the basic comb method (GECC 3.44)
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*/
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static int ecp_mul_comb_core( const ecp_group *grp, ecp_point *R,
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const ecp_point T[], const signed char x[],
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size_t d )
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{
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int ret;
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ecp_point Txi;
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size_t i;
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ecp_point_init( &Txi );
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/* Avoid useless doubling/addition of 0 by better initialisation */
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i = d - 1;
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MPI_CHK( ecp_select_comb( grp, R, T, x[i] ) );
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while( i-- != 0 )
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{
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MPI_CHK( ecp_double_jac( grp, R, R ) );
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MPI_CHK( ecp_select_comb( grp, &Txi, T, x[i] ) );
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MPI_CHK( ecp_add_mixed( grp, R, R, &Txi, +1 ) );
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}
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cleanup:
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ecp_point_free( &Txi );
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return( ret );
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}
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/*
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* Multiplication using the comb method, WIP
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*/
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int ecp_mul_comb( ecp_group *grp, ecp_point *R,
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const mpi *m, const ecp_point *P,
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int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
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{
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int ret;
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unsigned char w, m_is_odd, p_eq_g;
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size_t pre_len, d, i;
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signed char k[100]; // TODO
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ecp_point Q, *T = NULL, S[2];
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mpi M;
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(void) f_rng;
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(void) p_rng; // TODO
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if( mpi_cmp_int( m, 0 ) < 0 || mpi_msb( m ) > grp->nbits )
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return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
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mpi_init( &M );
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ecp_point_init( &Q );
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ecp_point_init( &S[0] );
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ecp_point_init( &S[1] );
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/*
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* Check if P == G
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*/
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p_eq_g = ( mpi_cmp_int( &P->Z, 1 ) == 0 &&
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mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 &&
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mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 );
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/* TODO: adjust exact value */
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w = grp->nbits >= 192 ? 5 : 2;
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pre_len = 1U << w;
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d = ( grp->nbits + w - 1 ) / w;
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/*
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* Prepare precomputed points: if P == G we want to
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* use grp->T if already initialized, or initiliaze it.
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*/
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if( ! p_eq_g || grp->T == NULL )
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{
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T = (ecp_point *) polarssl_malloc( pre_len * sizeof( ecp_point ) );
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if( T == NULL )
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{
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ret = POLARSSL_ERR_ECP_MALLOC_FAILED;
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goto cleanup;
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}
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for( i = 0; i < pre_len; i++ )
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ecp_point_init( &T[i] );
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MPI_CHK( ecp_precompute_comb( grp, T, P, w, d ) );
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if( p_eq_g )
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{
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grp->T = T;
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grp->T_size = pre_len;
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}
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}
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else
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{
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T = grp->T;
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/* Should never happen, but we want to be extra sure */
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if( pre_len != grp->T_size )
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{
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ret = POLARSSL_ERR_ECP_BAD_INPUT_DATA;
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goto cleanup;
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}
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}
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/*
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* Make sure M is odd (M = m + 1 or M = m + 2)
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* later we'll get m * P by subtracting P or 2 * P to M * P.
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*/
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m_is_odd = ( mpi_get_bit( m, 0 ) == 1 );
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MPI_CHK( mpi_copy( &M, m ) );
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MPI_CHK( mpi_add_int( &M, &M, 1 + m_is_odd ) );
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/*
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* Go for comb multiplication, Q = M * P
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*/
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ecp_comb_fixed( k, d, w, &M );
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ecp_mul_comb_core( grp, &Q, T, k, d );
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/*
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* Now get m * P from M * P
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*/
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MPI_CHK( ecp_copy( &S[0], P ) );
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MPI_CHK( ecp_add( grp, &S[1], P, P ) );
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MPI_CHK( ecp_sub( grp, R, &Q, &S[m_is_odd] ) );
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cleanup:
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if( T != NULL && ! p_eq_g )
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{
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for( i = 0; i < pre_len; i++ )
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ecp_point_free( &T[i] );
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polarssl_free( T );
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}
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ecp_point_free( &S[1] );
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ecp_point_free( &S[0] );
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ecp_point_free( &Q );
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mpi_free( &M );
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return( ret );
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}
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/*
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* Check that a point is valid as a public key (SEC1 3.2.3.1)
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*/
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