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diff --git a/src/multisig/multisig_tx_builder_ringct.h b/src/multisig/multisig_tx_builder_ringct.h
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+// Copyright (c) 2021, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
+#pragma once
+
+#include "ringct/rctTypes.h"
+
+#include <set>
+#include <vector>
+
+namespace cryptonote {
+
+class transaction;
+struct tx_source_entry;
+struct tx_destination_entry;
+struct account_keys;
+
+}
+
+namespace multisig {
+
+namespace signing {
+
+class CLSAG_context_t;
+
+// number of parallel signing nonces to use per signer (2 nonces as in musig2 and FROST)
+constexpr std::size_t kAlphaComponents = 2;
+
+class tx_builder_ringct_t final {
+private:
+  // the tx builder has been initialized
+  bool initialized;
+  // the tx builder is 'reconstructing' a tx that has already been created using this object
+  bool reconstruction;
+  // cached: mu_P*(local keys and sender-receiver secret and subaddress material) + mu_C*(commitment-to-zero secret)
+  // - these are only used for the initial building of a tx (not reconstructions)                                           
+  rct::keyV cached_w;
+  // contexts for making CLSAG challenges with multisig nonces
+  std::vector<CLSAG_context_t> CLSAG_contexts;
+public:
+  tx_builder_ringct_t();
+  ~tx_builder_ringct_t();
+
+  // prepare an unsigned transaction (and get tx privkeys for outputs)
+  bool init(
+    const cryptonote::account_keys& account_keys,
+    const std::vector<std::uint8_t>& extra,
+    const std::uint64_t unlock_time,
+    const std::uint32_t subaddr_account,
+    const std::set<std::uint32_t>& subaddr_minor_indices,
+    std::vector<cryptonote::tx_source_entry>& sources,
+    std::vector<cryptonote::tx_destination_entry>& destinations,
+    const cryptonote::tx_destination_entry& change,
+    const rct::RCTConfig& rct_config,
+    const bool use_rct,
+    const bool reconstruction,
+    crypto::secret_key& tx_secret_key,
+    std::vector<crypto::secret_key>& tx_aux_secret_keys,
+    cryptonote::transaction& unsigned_tx
+  );
+
+  // get the first partial signature for the specified input ('source')
+  bool first_partial_sign(
+    const std::size_t source,
+    const rct::keyV& total_alpha_G,
+    const rct::keyV& total_alpha_H,
+    const rct::keyV& alpha,
+    rct::key& c_0,
+    rct::key& s
+  );
+
+  // get intermediate partial signatures for all the inputs
+  bool next_partial_sign(
+    const rct::keyM& total_alpha_G,
+    const rct::keyM& total_alpha_H,
+    const rct::keyM& alpha,
+    const rct::key& x,
+    rct::keyV& c_0,
+    rct::keyV& s
+  );
+
+  // finalize an unsigned transaction (add challenges and real responses to incomplete CLSAG signatures)
+  static bool finalize_tx(
+    const std::vector<cryptonote::tx_source_entry>& sources,
+    const rct::keyV& c_0,
+    const rct::keyV& s,
+    cryptonote::transaction& unsigned_tx
+  );
+};
+
+} //namespace signing
+
+} //namespace multisig