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Added ecp_check_pubkey().

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Manuel Pégourié-Gonnard
2012-11-24 12:05:44 +01:00
committed by Paul Bakker
parent c554e9acf1
commit 1c33057a63
4 changed files with 123 additions and 0 deletions
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45
library/ecp.c
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@ -467,6 +467,51 @@ int ecp_use_known_dp( ecp_group *grp, size_t index )
while( mpi_cmp_mpi( &N, &grp->P ) >= 0 ) \
MPI_CHK( mpi_sub_mpi( &N, &N, &grp->P ) )
/*
* Check that a point is valid as a public key (SEC1 3.2.3.1)
*/
int ecp_check_pubkey( const ecp_group *grp, const ecp_point *pt )
{
int ret;
mpi YY, RHS;
if( mpi_cmp_int( &pt->Z, 0 ) == 0 )
return( POLARSSL_ERR_ECP_GENERIC );
/*
* pt coordinates must be normalized for our checks
*/
if( mpi_cmp_int( &pt->Z, 1 ) != 0 )
return( POLARSSL_ERR_ECP_GENERIC );
if( mpi_cmp_int( &pt->X, 0 ) < 0 ||
mpi_cmp_int( &pt->Y, 0 ) < 0 ||
mpi_cmp_mpi( &pt->X, &grp->P ) >= 0 ||
mpi_cmp_mpi( &pt->Y, &grp->P ) >= 0 )
return( POLARSSL_ERR_ECP_GENERIC );
mpi_init( &YY ); mpi_init( &RHS );
/*
* YY = Y^2
* RHS = X (X^2 - 3) + B = X^3 - 3X + B
*/
MPI_CHK( mpi_mul_mpi( &YY, &pt->Y, &pt->Y ) ); MOD_MUL( YY );
MPI_CHK( mpi_mul_mpi( &RHS, &pt->X, &pt->X ) ); MOD_MUL( RHS );
MPI_CHK( mpi_sub_int( &RHS, &RHS, 3 ) ); MOD_SUB( RHS );
MPI_CHK( mpi_mul_mpi( &RHS, &RHS, &pt->X ) ); MOD_MUL( RHS );
MPI_CHK( mpi_add_mpi( &RHS, &RHS, &grp->B ) ); MOD_ADD( RHS );
if( mpi_cmp_mpi( &YY, &RHS ) != 0 )
ret = POLARSSL_ERR_ECP_GENERIC;
cleanup:
mpi_free( &YY ); mpi_free( &RHS );
return( ret );
}
/*
* Normalize jacobian coordinates so that Z == 0 || Z == 1 (GECC 3.2.1)
*/