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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
View file

@ -52,18 +52,17 @@ ecp_point;
/**
* \brief ECP group structure
*
* The curves we consider are defined by y^2 = x^3 - 3x + b mod p,
* and a generator for a large subgroup is fixed.
* The curves we consider are defined by y^2 = x^3 - 3x + B mod P,
* 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
* done using a generic algorithm.
* pbits and nbits must be the size of P and N in bits.
*
* If modp is not NULL, pbits must be the size of P in bits and modp
* must be a function that takes an mpi in the range 0..2^(2*pbits) and
* transforms it in-place in an integer of little more than pbits, so
* that the integer may be efficiently brought in the 0..P range by a
* few additions or substractions. It must return 0 on success and a
* POLARSSL_ERR_ECP_XXX error on failure.
* If modp is NULL, reduction modulo P is done using a generic
* algorithm. Otherwise, it must point to a function that takes an mpi
* in the range 0..2^(2*pbits) and transforms it in-place in an integer
* of little more than pbits, so that the integer may be efficiently
* brought in the 0..P range by a few additions or substractions. It
* must return 0 on success and a POLARSSL_ERR_ECP_XXX error on failure.
*/
typedef struct
{
@ -71,8 +70,9 @@ typedef struct
mpi B; /*!< constant term in the equation */
ecp_point G; /*!< generator of the subgroup used */
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 */
unsigned pbits; /*!< number of bits in P */
}
ecp_group;
@ -158,6 +158,8 @@ int ecp_point_read_string( ecp_point *P, int radix,
* \param n The generator's order
*
* \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,
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 );
mpi_init( &grp->N );
grp->modp = NULL;
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( mpi_read_string( &grp->N, radix, n ) );
grp->pbits = mpi_msb( &grp->P );
grp->nbits = mpi_msb( &grp->N );
cleanup:
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 )
{
@ -394,7 +400,6 @@ int ecp_use_known_dp( ecp_group *grp, size_t index )
{
case POLARSSL_ECP_DP_SECP192R1:
grp->modp = ecp_mod_p192;
grp->pbits = 192;
return( ecp_group_read_string( grp, 16,
SECP192R1_P, SECP192R1_B,
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:
grp->modp = ecp_mod_p521;
grp->pbits = 521;
return( ecp_group_read_string( grp, 16,
SECP521R1_P, SECP521R1_B,
SECP521R1_GX, SECP521R1_GY, SECP521R1_N ) );