Fix a compliance issue in signature encoding
The issue is not present in the normal path because asn1write_mpi() does it
automatically, but we're not using that here...
diff --git a/library/pk_wrap.c b/library/pk_wrap.c
index 762dbfb..5e83602 100644
--- a/library/pk_wrap.c
+++ b/library/pk_wrap.c
@@ -807,8 +807,16 @@
*p -= len;
memmove( *p, start, len );
+ /* ASN.1 DER encoding requires minimal length, so skip leading 0s.
+ * Neither r nor s can be 0, so we can assume len > 0 at all times. */
+ while( **p == 0x00 )
+ {
+ ++(*p);
+ --len;
+ }
+
/* if the msb is 1, ASN.1 requires that we prepend a 0.
- * we're never called with n_len == 0, so we can always read back a byte */
+ * Neither r nor s can be 0, so we can assume len > 0 at all times. */
if( **p & 0x80 )
{
if( *p - start < 1 )