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Adapt key checking functions for Curve25519

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Manuel Pégourié-Gonnard 2013-12-04 11:08:01 +01:00
parent 661536677b
commit 312d2e8ea2
4 changed files with 125 additions and 19 deletions
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58
library/ecp.c
View file

@ -176,6 +176,14 @@ const ecp_curve_info *ecp_curve_info_from_name( const char *name )
return( NULL );
}
/*
* Tell if a group structure is associated to a Montgomery curve
*/
static inline int ecp_is_montgomery( const ecp_group *grp )
{
return( grp->G.X.p != NULL && grp->G.Y.p == NULL );
}
/*
* Initialize (the components of) a point
*/
@ -1498,22 +1506,31 @@ cleanup:
}
/*
* Check that a point is valid as a public key (SEC1 3.2.3.1)
* Check that a point is valid as a public key
*/
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_INVALID_KEY );
/*
* pt coordinates must be normalized for our checks
*/
/* Must use affine coordinates */
if( mpi_cmp_int( &pt->Z, 1 ) != 0 )
return( POLARSSL_ERR_ECP_INVALID_KEY );
if( ecp_is_montgomery( grp ) )
{
/* Just check X is the correct number of bytes */
if( mpi_size( &pt->X ) > ( grp->nbits + 7 ) / 8 )
return( POLARSSL_ERR_ECP_INVALID_KEY );
return( 0 );
}
/*
* Ok, so we have a short Weierstrass curve as in SEC1 3.2.3.1
*/
/* pt coordinates must be normalized for our checks */
if( mpi_cmp_int( &pt->X, 0 ) < 0 ||
mpi_cmp_int( &pt->Y, 0 ) < 0 ||
mpi_cmp_mpi( &pt->X, &grp->P ) >= 0 ||
@ -1522,6 +1539,12 @@ int ecp_check_pubkey( const ecp_group *grp, const ecp_point *pt )
mpi_init( &YY ); mpi_init( &RHS );
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_INVALID_KEY );
/*
* YY = Y^2
* RHS = X (X^2 + A) + B = X^3 + A X + B
@ -1543,13 +1566,26 @@ cleanup:
}
/*
* Check that an mpi is valid as a private key (SEC1 3.2)
* Check that an mpi is valid as a private key
*/
int ecp_check_privkey( const ecp_group *grp, const mpi *d )
{
/* We want 1 <= d <= N-1 */
if ( mpi_cmp_int( d, 1 ) < 0 || mpi_cmp_mpi( d, &grp->N ) >= 0 )
return( POLARSSL_ERR_ECP_INVALID_KEY );
if( ecp_is_montgomery( grp ) )
{
/* see the Curve25519 paper */
if( mpi_get_bit( d, 0 ) != 0 ||
mpi_get_bit( d, 1 ) != 0 ||
mpi_get_bit( d, 2 ) != 0 ||
mpi_msb( d ) - 1 != grp->nbits ) /* mpi_msb is one-based! */
return( POLARSSL_ERR_ECP_INVALID_KEY );
}
else
{
/* see SEC1 3.2 */
if( mpi_cmp_int( d, 1 ) < 0 ||
mpi_cmp_mpi( d, &grp->N ) >= 0 )
return( POLARSSL_ERR_ECP_INVALID_KEY );
}
return( 0 );
}

6
library/ecp_curves.c
View file

@ -357,6 +357,12 @@ static int ecp_use_curve25519( ecp_group *grp )
MPI_CHK( mpi_sub_int( &grp->P, &grp->P, 19 ) );
grp->pbits = mpi_msb( &grp->P );
/* Y intentionaly not set, since we use x/z coordinates.
* This is used as a marker to identify Montgomery curves! */
MPI_CHK( mpi_lset( &grp->G.X, 9 ) );
MPI_CHK( mpi_lset( &grp->G.Z, 1 ) );
mpi_free( &grp->G.Y );
/* Actually, the required msb for private keys */
grp->nbits = 254;