multisig_account.h

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// Copyright (c) 2021-2022, The Monero Project
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#pragma once

#include "crypto/crypto.h"
#include "multisig_kex_msg.h"

#include <cstdint>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>


namespace multisig
{
  using multisig_keyset_map_memsafe_t = 
    std::unordered_map<crypto::public_key_memsafe, std::unordered_set<crypto::public_key>>;

  class multisig_account final
  {
  public:
  //constructors
    // default constructor
    multisig_account() = default;

    multisig_account(const crypto::secret_key &base_privkey,
      const crypto::secret_key &base_common_privkey);

    // reconstruct from full account details (not recommended)
    multisig_account(const std::uint32_t threshold,
      std::vector<crypto::public_key> signers,
      const crypto::secret_key &base_privkey,
      const crypto::secret_key &base_common_privkey,
      std::vector<crypto::secret_key> multisig_privkeys,
      const crypto::secret_key &common_privkey,
      const crypto::public_key &multisig_pubkey,
      const crypto::public_key &common_pubkey,
      const std::uint32_t kex_rounds_complete,
      multisig_keyset_map_memsafe_t kex_origins_map,
      std::string next_round_kex_message);

    // copy constructor: default

  //destructor: default
    ~multisig_account() = default;

  //overloaded operators: none

  //getters
    // get threshold
    std::uint32_t get_threshold() const { return m_threshold; }
    // get signers
    const std::vector<crypto::public_key>& get_signers() const { return m_signers; }
    // get base privkey
    const crypto::secret_key& get_base_privkey() const { return m_base_privkey; }
    // get base pubkey
    const crypto::public_key& get_base_pubkey() const { return m_base_pubkey; }
    // get base common privkey
    const crypto::secret_key& get_base_common_privkey() const { return m_base_common_privkey; }
    // get multisig privkeys
    const std::vector<crypto::secret_key>& get_multisig_privkeys() const { return m_multisig_privkeys; }
    // get common privkey
    const crypto::secret_key& get_common_privkey() const { return m_common_privkey; }
    // get multisig pubkey
    const crypto::public_key& get_multisig_pubkey() const { return m_multisig_pubkey; }
    // get common pubkey
    const crypto::public_key& get_common_pubkey() const { return m_common_pubkey; }
    // get kex rounds complete
    std::uint32_t get_kex_rounds_complete() const { return m_kex_rounds_complete; }
    // get kex keys to origins map
    const multisig_keyset_map_memsafe_t& get_kex_keys_to_origins_map() const { return m_kex_keys_to_origins_map; }
    // get the kex msg for the next round
    const std::string& get_next_kex_round_msg() const { return m_next_round_kex_message; }

  //account status functions
    // account has been intialized, and the account holder can use the 'common' key
    bool account_is_active() const;
    // account has gone through main kex rounds, only remaining step is to verify all other participants are ready
    bool main_kex_rounds_done() const;
    // account is ready to make multisig signatures
    bool multisig_is_ready() const;

  //account helpers
  private:
    // set the threshold (M) and signers (N)
    void set_multisig_config(const std::size_t threshold, std::vector<crypto::public_key> signers);

  //account mutators: key exchange to set up account
  public:
    void initialize_kex(const std::uint32_t threshold,
      std::vector<crypto::public_key> signers,
      const std::vector<multisig_kex_msg> &expanded_msgs_rnd1);
    void kex_update(const std::vector<multisig_kex_msg> &expanded_msgs,
      const bool force_update_use_with_caution = false);

  private:
    // implementation of kex_update() (non-transactional)
    void kex_update_impl(const std::vector<multisig_kex_msg> &expanded_msgs, const bool incomplete_signer_set);
    void initialize_kex_update(const std::vector<multisig_kex_msg> &expanded_msgs,
      const std::uint32_t kex_rounds_required,
      std::vector<crypto::public_key> &exclude_pubkeys_out);
    void finalize_kex_update(const std::uint32_t kex_rounds_required,
      multisig_keyset_map_memsafe_t result_keys_to_origins_map);

  //member variables
  private:
    // [M] minimum number of co-signers to sign a message with the aggregate pubkey
    std::uint32_t m_threshold{0};
    // [N] base keys of all participants in the multisig (used to initiate key exchange, and as participant ids for msg signing)
    std::vector<crypto::public_key> m_signers;

    // base keypair of the participant
    // - used for signing messages, as the initial base key for key exchange, and to make DH derivations for key exchange
    crypto::secret_key m_base_privkey;
    crypto::public_key m_base_pubkey;
    // common base privkey, used to produce the aggregate common privkey
    crypto::secret_key m_base_common_privkey;

    // the account's private key shares of the multisig address
    // TODO: also record which other signers have these privkeys, to enable aggregation signing (instead of round-robin)
    std::vector<crypto::secret_key> m_multisig_privkeys;
    // a privkey owned by all multisig participants (e.g. a cryptonote view key)
    crypto::secret_key m_common_privkey;
    // the multisig public key (e.g. a cryptonote spend key)
    crypto::public_key m_multisig_pubkey;
    // the common public key (e.g. a view spend key)
    crypto::public_key m_common_pubkey;

    // number of key exchange rounds that have been completed (all messages for the round collected and processed)
    std::uint32_t m_kex_rounds_complete{0};
    // this account's pubkeys for the in-progress key exchange round
    // - either DH derivations (intermediate rounds), H(derivation)*G (final round), empty (when kex is done)
    multisig_keyset_map_memsafe_t m_kex_keys_to_origins_map;
    // the account's message for the in-progress key exchange round
    std::string m_next_round_kex_message;
  };

  std::uint32_t multisig_kex_rounds_required(const std::uint32_t num_signers, const std::uint32_t threshold);

  std::uint32_t multisig_setup_rounds_required(const std::uint32_t num_signers, const std::uint32_t threshold);
} //namespace multisig