Safeguard against calling p255 reduction with single-width MPI
(In this case, there's nothing to do anyway since we only do a
quasi-reduction to N+1 limbs)
Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index 6bc8591..5f541ad 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -5223,7 +5223,7 @@
/* Helper references for top part of N */
mbedtls_mpi_uint * const NT_p = N->p + P255_WIDTH;
unsigned const NT_n = N->n - P255_WIDTH;
- if( NT_n > P255_WIDTH )
+ if( NT_n == 0 || NT_n > P255_WIDTH )
return( 0 );
/* Split N as N + 2^256 M */