plonk: created a new transcript_hasher.hpp file with just a comment t…

…hat describes the interface of a common transcript hasher. addresses step 1. from comment #61 (comment) of PR#61.

libsnark/transcript_hasher/transcript_hasher.hpp

@@ -0,0 +1,32 @@
+/** @file
+ *****************************************************************************
+ * @author     This file is part of libff, developed by Clearmatics Ltd
+ *             (originally developed by SCIPR Lab) and contributors
+ *             (see AUTHORS).
+ * @copyright  MIT license (see LICENSE file)
+ *****************************************************************************/
+
+#ifndef LIBSNARK_TRANSCRIPT_HASHER_TRANSCRIPT_HASHER_HPP_
+#define LIBSNARK_TRANSCRIPT_HASHER_TRANSCRIPT_HASHER_HPP_
+
+// // interface for a common transcript_hasher class used to implement
+// // functionality for hashing the communication transcript in ZK proof
+// // systems under ./zk_proof_systems
+// template<typename ppT> class transcript_hasher
+// {
+// public:
+//     transcript_hasher();
+//
+//     // add an Fr element to the transcript buffer for hashing
+//     void add_element(const libff::Fr<ppT> &element);
+//     // add the coordinates of a G1 curve point to the transcript buffer for
+//     // hashing
+//     void add_element(const libff::G1<ppT> &element);
+//     // add the coordinates of a G2 curve point to the transcript buffer for
+//     // hashing
+//     void add_element(const libff::G2<ppT> &element);
+//     // return the hash value of the communication transcript
+//     libff::Fr<ppT> get_hash();
+// };
+
+#endif // LIBSNARK_ZK_PROOF_SYSTEMS_PLONK_SRS_HPP_