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diff --git a/src/multisig/multisig_kex_msg.h b/src/multisig/multisig_kex_msg.h
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+++ b/src/multisig/multisig_kex_msg.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 "crypto/crypto.h"
+
+#include <cstdint>
+#include <vector>
+
+
+namespace multisig
+{
+  ////
+  // multisig key exchange message
+  // - can parse and validate an input message
+  // - can construct and sign a new message
+  //
+  // msg_content = kex_round | signing_pubkey | expand(msg_pubkeys) | OPTIONAL msg_privkey
+  // msg_to_sign = versioning-domain-sep | msg_content
+  // msg = versioning-domain-sep | b58(msg_content | crypto_sig[signing_privkey](msg_to_sign))
+  //
+  // note: round 1 messages will contain a private key (e.g. for the aggregate multisig private view key)
+  ///
+  class multisig_kex_msg final
+  {
+  //member types: none
+
+  //constructors
+  public:
+    // default constructor
+    multisig_kex_msg() = default;
+
+    // construct from info
+    multisig_kex_msg(const std::uint32_t round,
+      const crypto::secret_key &signing_privkey,
+      std::vector<crypto::public_key> msg_pubkeys,
+      const crypto::secret_key &msg_privkey = crypto::null_skey);
+
+    // construct from string
+    multisig_kex_msg(std::string msg);
+
+    // copy constructor: default
+
+  //destructor: default
+    ~multisig_kex_msg() = default;
+
+  //overloaded operators: none
+
+  //member functions
+    // get msg string
+    const std::string& get_msg() const { return m_msg; }
+    // get kex round
+    std::uint32_t get_round() const { return m_kex_round; }
+    // get msg pubkeys
+    const std::vector<crypto::public_key>& get_msg_pubkeys() const { return m_msg_pubkeys; }
+    // get msg privkey
+    const crypto::secret_key& get_msg_privkey() const { return m_msg_privkey; }
+    // get msg signing pubkey
+    const crypto::public_key& get_signing_pubkey() const { return m_signing_pubkey; }
+
+  private:
+    // msg_to_sign = versioning-domain-sep | kex_round | signing_pubkey | expand(msg_pubkeys) | OPTIONAL msg_privkey
+    crypto::hash get_msg_to_sign() const;
+    // set: msg string based on msg contents, signing pubkey based on input privkey
+    void construct_msg(const crypto::secret_key &signing_privkey);
+    // parse msg string into parts, validate contents and signature
+    void parse_and_validate_msg();
+
+  //member variables
+  private:
+    // message as string
+    std::string m_msg;
+
+    // key exchange round this msg was produced for
+    std::uint32_t m_kex_round;
+    // pubkeys stored in msg
+    std::vector<crypto::public_key> m_msg_pubkeys;
+    // privkey stored in msg (if kex round 1)
+    crypto::secret_key m_msg_privkey;
+    // pubkey used to sign this msg
+    crypto::public_key m_signing_pubkey;
+  };
+} //namespace multisig