zkSNARK: Authenticate h_sig with a_sk
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@ -23,8 +23,13 @@ private:
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// Input note gadgets
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boost::array<std::shared_ptr<input_note_gadget<FieldT>>, NumInputs> zk_input_notes;
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boost::array<std::shared_ptr<PRF_pk_gadget<FieldT>>, NumInputs> zk_hmac_authentication;
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public:
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// PRF_pk only has a 1-bit domain separation "nonce"
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// for different hmacs.
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BOOST_STATIC_ASSERT(NumInputs <= 2);
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joinsplit_gadget(protoboard<FieldT> &pb) : gadget<FieldT>(pb) {
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// Verification
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{
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@ -80,6 +85,17 @@ public:
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ZERO,
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zk_input_nullifiers[i]
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));
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// The input keys authenticate h_sig to prevent
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// malleability.
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zk_hmac_authentication[i].reset(new PRF_pk_gadget<FieldT>(
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pb,
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ZERO,
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zk_input_notes[i]->a_sk->bits,
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zk_h_sig->bits,
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i ? true : false,
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zk_input_hmacs[i]
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));
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}
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}
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@ -94,6 +110,9 @@ public:
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for (size_t i = 0; i < NumInputs; i++) {
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// Constrain the JoinSplit input constraints.
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zk_input_notes[i]->generate_r1cs_constraints();
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// Authenticate h_sig with a_sk
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zk_hmac_authentication[i]->generate_r1cs_constraints();
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}
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}
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@ -109,9 +128,18 @@ public:
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// Witness `zero`
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this->pb.val(ZERO) = FieldT::zero();
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// Witness h_sig
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zk_h_sig->bits.fill_with_bits(
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this->pb,
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uint256_to_bool_vector(h_sig)
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);
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for (size_t i = 0; i < NumInputs; i++) {
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// Witness the input information.
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zk_input_notes[i]->generate_r1cs_witness(inputs[i].key, inputs[i].note);
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// Witness hmacs
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zk_hmac_authentication[i]->generate_r1cs_witness();
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}
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// This happens last, because only by now are all the
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@ -131,11 +159,11 @@ public:
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std::vector<bool> verify_inputs;
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insert_uint256(verify_inputs, uint256()); // TODO: rt
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insert_uint256(verify_inputs, uint256()); // TODO: h_sig
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insert_uint256(verify_inputs, h_sig);
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for (size_t i = 0; i < NumInputs; i++) {
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insert_uint256(verify_inputs, nullifiers[i]);
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insert_uint256(verify_inputs, uint256()); // TODO: hmac
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insert_uint256(verify_inputs, hmacs[i]);
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}
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for (size_t i = 0; i < NumOutputs; i++) {
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@ -29,13 +29,14 @@ public:
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template<typename FieldT>
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class input_note_gadget : public note_gadget<FieldT> {
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public:
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std::shared_ptr<digest_variable<FieldT>> a_sk;
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private:
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std::shared_ptr<digest_variable<FieldT>> a_pk;
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std::shared_ptr<digest_variable<FieldT>> rho;
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std::shared_ptr<PRF_addr_a_pk_gadget<FieldT>> spend_authority;
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std::shared_ptr<PRF_nf_gadget<FieldT>> expose_nullifiers;
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public:
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std::shared_ptr<digest_variable<FieldT>> a_sk;
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input_note_gadget(
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protoboard<FieldT>& pb,
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@ -95,3 +95,24 @@ public:
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PRF_gadget<FieldT>::generate_r1cs_witness();
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}
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};
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template<typename FieldT>
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class PRF_pk_gadget : public PRF_gadget<FieldT> {
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public:
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PRF_pk_gadget(
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protoboard<FieldT>& pb,
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pb_variable<FieldT>& ZERO,
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pb_variable_array<FieldT>& a_sk,
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pb_variable_array<FieldT>& h_sig,
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bool nonce,
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std::shared_ptr<digest_variable<FieldT>> result
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) : PRF_gadget<FieldT>(pb, ZERO, 0, nonce, 0, 0, a_sk, h_sig, result) {}
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void generate_r1cs_constraints() {
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PRF_gadget<FieldT>::generate_r1cs_constraints();
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}
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void generate_r1cs_witness() {
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PRF_gadget<FieldT>::generate_r1cs_witness();
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}
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};
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