openssl: Add helper function to convert BIGNUMs to chunks

src/libstrongswan/plugins/openssl/openssl_util.h

@@ -66,6 +66,15 @@ bool openssl_bn_cat(int len, BIGNUM *a, BIGNUM *b, chunk_t *chunk);
  */
 bool openssl_bn_split(chunk_t chunk, BIGNUM *a, BIGNUM *b);
 
+/**
+ * Exports the given bignum (assumed to be a positive number) to a chunk in
+ * two's complement format (i.e. a zero byte is added if the MSB is set).
+ *
+ * @param bn		the BIGNUM to export
+ * @param chunk		the chunk (data gets allocated)
+ * @return			TRUE on success, FALSE otherwise
+ */
+bool openssl_bn2chunk(BIGNUM *bn, chunk_t *chunk);
 
 /**
  * Allocate a chunk using the i2d function of a given object