working make_return_tx() code

src/carrot_core/enote_utils.h

@@ -138,7 +138,7 @@ void make_sparc_return_privkey(const unsigned char s_sender_receiver_unctx[32],
     crypto::secret_key &return_privkey_out);
 /**
 * brief: make_sparc_return_pubkey_encryption_mask - used for hiding return pubkey
-*    vt = H_32(s_sr || input_context || Ko)
+*    m_return = H_32(s_sr || input_context || Ko)
 * param: s_sender_receiver_unctx - s_sr
 * param: input_context - input_context
 * param: onetime_address - Ko

src/carrot_core/payment_proposal.cpp

@@ -401,6 +401,63 @@ void get_output_proposal_special_v1(const CarrotPaymentProposalSelfSendV1 &propo
     output_enote_out.amount                       = proposal.amount;
 }
 //-------------------------------------------------------------------------------------------------------------------
+void get_output_proposal_return_v1(const CarrotPaymentProposalV1 &proposal,
+                                   const crypto::key_image &tx_first_key_image,
+                                   RCTOutputEnoteProposal &output_enote_out,
+                                   encrypted_payment_id_t &encrypted_payment_id_out)
+{
+    // 1. sanity checks
+    CARROT_CHECK_AND_THROW(proposal.randomness != null_anchor,
+        missing_randomness, "invalid randomness for janus anchor (zero).");
+
+    // 2. input context: input_context = "R" || KI_1
+    const input_context_t input_context = make_carrot_input_context(tx_first_key_image);
+
+    // 3. make D_e and do external ECDH
+    mx25519_pubkey s_sender_receiver_unctx; auto dhe_wiper = auto_wiper(s_sender_receiver_unctx);
+    get_normal_proposal_ecdh_parts(proposal,
+        input_context,
+        output_enote_out.enote.enote_ephemeral_pubkey,
+        s_sender_receiver_unctx);
+
+    // 4. build the output enote address pieces
+    crypto::hash s_sender_receiver; auto q_wiper = auto_wiper(s_sender_receiver);
+    // HERE BE DRAGONS!!!
+    // SRCG: the following call needs the "destination" parameter adjusted for return_payment
+    get_external_output_proposal_parts(s_sender_receiver_unctx,
+                                       proposal.destination.address_spend_pubkey,
+                                       proposal.destination.payment_id,
+                                       proposal.amount,
+                                       CarrotEnoteType::PAYMENT,
+                                       output_enote_out.enote.enote_ephemeral_pubkey,
+                                       input_context,
+                                       false,
+                                       s_sender_receiver,
+                                       output_enote_out.amount_blinding_factor,
+                                       output_enote_out.enote.amount_commitment,
+                                       output_enote_out.enote.onetime_address,
+                                       output_enote_out.enote.amount_enc,
+                                       encrypted_payment_id_out,
+                                       output_enote_out.enote.view_tag);
+
+    // Override the onetime address
+    sc_add(to_bytes(output_enote_out.enote.onetime_address), to_bytes(proposal.destination.address_spend_pubkey), to_bytes(proposal.destination.address_view_pubkey));
+
+    // Recalculate the view tag : vt = H_3(s_sr || input_context || Ksra)
+    make_carrot_view_tag(s_sender_receiver_unctx.data, input_context, output_enote_out.enote.onetime_address, output_enote_out.enote.view_tag);
+
+    // LAND AHOY!!!
+    
+    // 5. anchor_enc = anchor XOR m_anchor
+    output_enote_out.enote.anchor_enc = encrypt_carrot_anchor(proposal.randomness,
+        s_sender_receiver,
+        output_enote_out.enote.onetime_address);
+
+    // 6. save the amount and first key image
+    output_enote_out.amount                   = proposal.amount;
+    output_enote_out.enote.tx_first_key_image = tx_first_key_image;
+}
+//-------------------------------------------------------------------------------------------------------------------
 void get_output_proposal_internal_v1(const CarrotPaymentProposalSelfSendV1 &proposal,
     const view_balance_secret_device &s_view_balance_dev,
     const crypto::key_image &tx_first_key_image,

src/carrot_core/payment_proposal.h

@@ -93,7 +93,7 @@ struct RCTOutputEnoteProposal
 
 /// equality operators
 bool operator==(const CarrotPaymentProposalV1 &a, const CarrotPaymentProposalV1 &b);
-/// equality operators
+  /// equality operators
 bool operator==(const CarrotPaymentProposalSelfSendV1 &a, const CarrotPaymentProposalSelfSendV1 &b);
 
 /**
@@ -134,7 +134,19 @@ void get_output_proposal_normal_v1(const CarrotPaymentProposalV1 &proposal,
     RCTOutputEnoteProposal &output_enote_out,
     encrypted_payment_id_t &encrypted_payment_id_out);
 /**
-* brief: get_output_proposal_v1 - convert the carrot proposal to an output proposal (external selfsend)
+* brief: get_output_proposal_return_v1 - convert the carrot proposal to an output proposal
+* param: proposal -
+* param: tx_first_key_image -
+* param: k_view_dev -
+* outparam: output_enote_out -
+* outparam: encrypted_payment_id_out - pid_enc
+*/
+void get_output_proposal_return_v1(const CarrotPaymentProposalV1 &proposal,
+                                   const crypto::key_image &tx_first_key_image,
+                                   RCTOutputEnoteProposal &output_enote_out,
+                                   encrypted_payment_id_t &encrypted_payment_id_out);
+/**
+* brief: get_output_proposal_special_v1 - convert the carrot proposal to an output proposal (external selfsend)
 * param: proposal -
 * param: k_view_dev -
 * param: tx_first_key_image -