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Start working on mod_p224

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(Prototype, works only on 32-bit and little-endian 64-bit.)
This commit is contained in:
Manuel Pégourié-Gonnard
2013-10-21 14:52:21 +02:00
parent cc67aee9c8
commit e783f06f73
3 changed files with 106 additions and 1 deletions
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88
library/ecp.c
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@ -543,6 +543,93 @@ cleanup:
#undef LAST
#endif /* POLARSSL_ECP_DP_SECP192R1_ENABLED */
#if defined(POLARSSL_ECP_DP_SECP521R1_ENABLED)
/* For now, prototype version for 32-bit or little-endian 64 bits only */
static inline void add32( uint32_t *dst, uint32_t src, signed char *carry )
{
*dst += src;
*carry += ( *dst < src );
}
static inline void sub32( uint32_t *dst, uint32_t src, signed char *carry )
{
*carry -= ( *dst < src );
*dst -= src;
}
#define A( i ) ( ((uint32_t *) N->p)[i] )
#define ADD( i ) add32( p, A( i ), &c );
#define SUB( i ) sub32( p, A( i ), &c );
#define NEXT \
p++; \
cc = c; \
c = 0; \
if( cc < 0 ) \
sub32( p, -cc, &c ); \
else \
add32( p, cc, &c );
#define LAST \
p++; \
*p = c > 0 ? c : 0; /* see fix_negative */ \
while( ++p < end ) \
*p = 0; \
if( c < 0 ) fix_negative( N, c, bits );
/*
* If the result is negative, we get it in the form c * 2^192 + N,
* with c negative and N positive (the c >= 0 case is handled by LAST).
*/
static inline int fix_negative( mpi *N, signed char c, size_t bits )
{
int ret;
mpi C;
mpi_init( &C );
MPI_CHK( mpi_lset( &C, c ) );
MPI_CHK( mpi_shift_l( &C, bits ) );
MPI_CHK( mpi_add_mpi( N, N, &C ) );
cleanup:
mpi_free( &C );
return( ret );
}
/*
* Fast quasi-reduction modulo p224 (FIPS 186-3 D.2.2)
*/
static int ecp_mod_p224( mpi *N )
{
int ret;
signed char c, cc;
uint32_t *p, *end;
size_t bits = 224;
/* Make sure we have the correct number of blocks */
MPI_CHK( mpi_grow( N, bits * 2 / 8 / sizeof( t_uint ) ) );
/* Currently assuming 32-bit ints, or 64-bits little-endian */
p = (uint32_t *) N->p;
end = (uint32_t *) (N->p + N->n);
SUB( 7 ); SUB( 11 ); NEXT; // A0 += -A7 - A11
SUB( 8 ); SUB( 12 ); NEXT; // A1 += -A8 - A12
SUB( 9 ); SUB( 13 ); NEXT; // A2 += -A9 - A13
SUB( 10 ); ADD( 7 ); ADD( 11 ); NEXT; // A3 += -A10 + A7 + A11
SUB( 11 ); ADD( 8 ); ADD( 12 ); NEXT; // A4 += -A11 + A8 + A12
SUB( 12 ); ADD( 9 ); ADD( 13 ); NEXT; // A5 += -A12 + A9 + A13
SUB( 13 ); ADD( 10 ); LAST; // A6 += -A13 + A10
cleanup:
return( ret );
}
#endif /* POLARSSL_ECP_DP_SECP224R1_ENABLED */
#if defined(POLARSSL_ECP_DP_SECP521R1_ENABLED)
/*
* Size of p521 in terms of t_uint
@ -761,6 +848,7 @@ int ecp_use_known_dp( ecp_group *grp, ecp_group_id id )
#if defined(POLARSSL_ECP_DP_SECP224R1_ENABLED)
case POLARSSL_ECP_DP_SECP224R1:
grp->modp = ecp_mod_p224;
return( ecp_group_read_string( grp, 16,
SECP224R1_P, SECP224R1_B,
SECP224R1_GX, SECP224R1_GY, SECP224R1_N ) );