Added ecp_check_pubkey().
diff --git a/library/ecp.c b/library/ecp.c
index 3bef06c..4073288 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -468,6 +468,51 @@
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)
*/
static int ecp_normalize( const ecp_group *grp, ecp_point *pt )