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Added a nbits member to ecp_group

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Manuel Pégourié-Gonnard 2012-11-18 13:19:07 +01:00 committed by Paul Bakker
parent 4bdd47d2cb
commit 773ed546a2
2 changed files with 21 additions and 15 deletions
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24
include/polarssl/ecp.h
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@ -52,18 +52,17 @@ ecp_point;
/** /**
* \brief ECP group structure * \brief ECP group structure
* *
* The curves we consider are defined by y^2 = x^3 - 3x + b mod p, * The curves we consider are defined by y^2 = x^3 - 3x + B mod P,
* and a generator for a large subgroup is fixed. * and a generator for a large subgroup of order N is fixed.
* *
* If modp is NULL, pbits will not be used, and reduction modulo P is * pbits and nbits must be the size of P and N in bits.
* done using a generic algorithm.
* *
* If modp is not NULL, pbits must be the size of P in bits and modp * If modp is NULL, reduction modulo P is done using a generic
* must be a function that takes an mpi in the range 0..2^(2*pbits) and * algorithm. Otherwise, it must point to a function that takes an mpi
* transforms it in-place in an integer of little more than pbits, so * in the range 0..2^(2*pbits) and transforms it in-place in an integer
* that the integer may be efficiently brought in the 0..P range by a * of little more than pbits, so that the integer may be efficiently
* few additions or substractions. It must return 0 on success and a * brought in the 0..P range by a few additions or substractions. It
* POLARSSL_ERR_ECP_XXX error on failure. * must return 0 on success and a POLARSSL_ERR_ECP_XXX error on failure.
*/ */
typedef struct typedef struct
{ {
@ -71,8 +70,9 @@ typedef struct
mpi B; /*!< constant term in the equation */ mpi B; /*!< constant term in the equation */
ecp_point G; /*!< generator of the subgroup used */ ecp_point G; /*!< generator of the subgroup used */
mpi N; /*!< the order of G */ mpi N; /*!< the order of G */
size_t pbits; /*!< number of bits in P */
size_t nbits; /*!< number of bits in N */
int (*modp)(mpi *); /*!< function for fast reduction mod P */ int (*modp)(mpi *); /*!< function for fast reduction mod P */
unsigned pbits; /*!< number of bits in P */
} }
ecp_group; ecp_group;
@ -158,6 +158,8 @@ int ecp_point_read_string( ecp_point *P, int radix,
* \param n The generator's order * \param n The generator's order
* *
* \return 0 if successful, or a POLARSSL_ERR_MPI_XXX error code * \return 0 if successful, or a POLARSSL_ERR_MPI_XXX error code
*
* \note Sets all fields except modp.
*/ */
int ecp_group_read_string( ecp_group *grp, int radix, int ecp_group_read_string( ecp_group *grp, int radix,
const char *p, const char *b, const char *p, const char *b,

12
library/ecp.c
View File

@ -64,8 +64,10 @@ void ecp_group_init( ecp_group *grp )
ecp_point_init( &grp->G ); ecp_point_init( &grp->G );
mpi_init( &grp->N ); mpi_init( &grp->N );
grp->modp = NULL;
grp->pbits = 0; grp->pbits = 0;
grp->nbits = 0;
grp->modp = NULL;
} }
/* /*
@ -155,12 +157,16 @@ int ecp_group_read_string( ecp_group *grp, int radix,
MPI_CHK( ecp_point_read_string( &grp->G, radix, gx, gy ) ); MPI_CHK( ecp_point_read_string( &grp->G, radix, gx, gy ) );
MPI_CHK( mpi_read_string( &grp->N, radix, n ) ); MPI_CHK( mpi_read_string( &grp->N, radix, n ) );
grp->pbits = mpi_msb( &grp->P );
grp->nbits = mpi_msb( &grp->N );
cleanup: cleanup:
return( ret ); return( ret );
} }
/* /*
* Wrapper around fast quasi-modp functions, with fall-back to mpi_mod_mpi * Wrapper around fast quasi-modp functions, with fall-back to mpi_mod_mpi.
* See the documentation of struct ecp_group.
*/ */
static int ecp_modp( mpi *N, const ecp_group *grp ) static int ecp_modp( mpi *N, const ecp_group *grp )
{ {
@ -394,7 +400,6 @@ int ecp_use_known_dp( ecp_group *grp, size_t index )
{ {
case POLARSSL_ECP_DP_SECP192R1: case POLARSSL_ECP_DP_SECP192R1:
grp->modp = ecp_mod_p192; grp->modp = ecp_mod_p192;
grp->pbits = 192;
return( ecp_group_read_string( grp, 16, return( ecp_group_read_string( grp, 16,
SECP192R1_P, SECP192R1_B, SECP192R1_P, SECP192R1_B,
SECP192R1_GX, SECP192R1_GY, SECP192R1_N ) ); SECP192R1_GX, SECP192R1_GY, SECP192R1_N ) );
@ -416,7 +421,6 @@ int ecp_use_known_dp( ecp_group *grp, size_t index )
case POLARSSL_ECP_DP_SECP521R1: case POLARSSL_ECP_DP_SECP521R1:
grp->modp = ecp_mod_p521; grp->modp = ecp_mod_p521;
grp->pbits = 521;
return( ecp_group_read_string( grp, 16, return( ecp_group_read_string( grp, 16,
SECP521R1_P, SECP521R1_B, SECP521R1_P, SECP521R1_B,
SECP521R1_GX, SECP521R1_GY, SECP521R1_N ) ); SECP521R1_GX, SECP521R1_GY, SECP521R1_N ) );