Add N/N multisig tx generation and signing

Scheme by luigi1111:

    Multisig for RingCT on Monero

    2 of 2

    User A (coordinator):
    Spendkey b,B
    Viewkey a,A (shared)

    User B:
    Spendkey c,C
    Viewkey a,A (shared)

    Public Address: C+B, A

    Both have their own watch only wallet via C+B, a

    A will coordinate spending process (though B could easily as well, coordinator is more needed for more participants)

    A and B watch for incoming outputs

    B creates "half" key images for discovered output D:
    I2_D = (Hs(aR)+c) * Hp(D)

    B also creates 1.5 random keypairs (one scalar and 2 pubkeys; one on base G and one on base Hp(D)) for each output, storing the scalar(k) (linked to D),
    and sending the pubkeys with I2_D.

    A also creates "half" key images:
    I1_D = (Hs(aR)+b) * Hp(D)

    Then I_D = I1_D + I2_D

    Having I_D allows A to check spent status of course, but more importantly allows A to actually build a transaction prefix (and thus transaction).

    A builds the transaction until most of the way through MLSAG_Gen, adding the 2 pubkeys (per input) provided with I2_D
    to his own generated ones where they are needed (secret row L, R).

    At this point, A has a mostly completed transaction (but with an invalid/incomplete signature). A sends over the tx and includes r,
    which allows B (with the recipient's address) to verify the destination and amount (by reconstructing the stealth address and decoding ecdhInfo).

    B then finishes the signature by computing ss[secret_index][0] = ss[secret_index][0] + k - cc[secret_index]*c (secret indices need to be passed as well).

    B can then broadcast the tx, or send it back to A for broadcasting. Once B has completed the signing (and verified the tx to be valid), he can add the full I_D
    to his cache, allowing him to verify spent status as well.

    NOTE:
    A and B *must* present key A and B to each other with a valid signature proving they know a and b respectively.
    Otherwise, trickery like the following becomes possible:
    A creates viewkey a,A, spendkey b,B, and sends a,A,B to B.
    B creates a fake key C = zG - B. B sends C back to A.
    The combined spendkey C+B then equals zG, allowing B to spend funds at any time!
    The signature fixes this, because B does not know a c corresponding to C (and thus can't produce a signature).

    2 of 3

    User A (coordinator)
    Shared viewkey a,A
    "spendkey" j,J

    User B
    "spendkey" k,K

    User C
    "spendkey" m,M

    A collects K and M from B and C
    B collects J and M from A and C
    C collects J and K from A and B

    A computes N = nG, n = Hs(jK)
    A computes O = oG, o = Hs(jM)

    B anc C compute P = pG, p = Hs(kM) || Hs(mK)
    B and C can also compute N and O respectively if they wish to be able to coordinate

    Address: N+O+P, A

    The rest follows as above. The coordinator possesses 2 of 3 needed keys; he can get the other
    needed part of the signature/key images from either of the other two.

    Alternatively, if secure communication exists between parties:
    A gives j to B
    B gives k to C
    C gives m to A

    Address: J+K+M, A

    3 of 3

    Identical to 2 of 2, except the coordinator must collect the key images from both of the others.
    The transaction must also be passed an additional hop: A -> B -> C (or A -> C -> B), who can then broadcast it
    or send it back to A.

    N-1 of N

    Generally the same as 2 of 3, except participants need to be arranged in a ring to pass their keys around
    (using either the secure or insecure method).
    For example (ignoring viewkey so letters line up):
    [4 of 5]
    User: spendkey
    A: a
    B: b
    C: c
    D: d
    E: e

    a -> B, b -> C, c -> D, d -> E, e -> A

    Order of signing does not matter, it just must reach n-1 users. A "remaining keys" list must be passed around with
    the transaction so the signers know if they should use 1 or both keys.
    Collecting key image parts becomes a little messy, but basically every wallet sends over both of their parts with a tag for each.
    Thia way the coordinating wallet can keep track of which images have been added and which wallet they come from. Reasoning:
    1. The key images must be added only once (coordinator will get key images for key a from both A and B, he must add only one to get the proper key actual key image)
    2. The coordinator must keep track of which helper pubkeys came from which wallet (discussed in 2 of 2 section). The coordinator
    must choose only one set to use, then include his choice in the "remaining keys" list so the other wallets know which of their keys to use.

    You can generalize it further to N-2 of N or even M of N, but I'm not sure there's legitimate demand to justify the complexity. It might
    also be straightforward enough to support with minimal changes from N-1 format.
    You basically just give each user additional keys for each additional "-1" you desire. N-2 would be 3 keys per user, N-3 4 keys, etc.

The process is somewhat cumbersome:

To create a N/N multisig wallet:

 - each participant creates a normal wallet
 - each participant runs "prepare_multisig", and sends the resulting string to every other participant
 - each participant runs "make_multisig N A B C D...", with N being the threshold and A B C D... being the strings received from other participants (the threshold must currently equal N)

As txes are received, participants' wallets will need to synchronize so that those new outputs may be spent:

 - each participant runs "export_multisig FILENAME", and sends the FILENAME file to every other participant
 - each participant runs "import_multisig A B C D...", with A B C D... being the filenames received from other participants

Then, a transaction may be initiated:

 - one of the participants runs "transfer ADDRESS AMOUNT"
 - this partly signed transaction will be written to the "multisig_monero_tx" file
 - the initiator sends this file to another participant
 - that other participant runs "sign_multisig multisig_monero_tx"
 - the resulting transaction is written to the "multisig_monero_tx" file again
 - if the threshold was not reached, the file must be sent to another participant, until enough have signed
 - the last participant to sign runs "submit_multisig multisig_monero_tx" to relay the transaction to the Monero network

1 files changed, 93 insertions, 7 deletions

diff --git a/src/wallet/wallet2.h b/src/wallet/wallet2.h
index 9b068df3c..97abb1476 100644
--- a/src/wallet/wallet2.h
+++ b/src/wallet/wallet2.h
@@ -145,7 +145,7 @@ namespace tools
     };
 
   private:
-    wallet2(const wallet2&) : m_run(true), m_callback(0), m_testnet(false), m_always_confirm_transfers(true), m_print_ring_members(false), m_store_tx_info(true), m_default_mixin(0), m_default_priority(0), m_refresh_type(RefreshDefault), m_auto_refresh(true), m_refresh_from_block_height(0), m_confirm_missing_payment_id(true), m_ask_password(true), m_min_output_count(0), m_min_output_value(0), m_merge_destinations(false), m_confirm_backlog(true), m_is_initialized(false),m_node_rpc_proxy(m_http_client, m_daemon_rpc_mutex) {}
+    wallet2(const wallet2&) : m_multisig_rescan_info(NULL), m_multisig_rescan_k(NULL), m_run(true), m_callback(0), m_testnet(false), m_always_confirm_transfers(true), m_print_ring_members(false), m_store_tx_info(true), m_default_mixin(0), m_default_priority(0), m_refresh_type(RefreshDefault), m_auto_refresh(true), m_refresh_from_block_height(0), m_confirm_missing_payment_id(true), m_ask_password(true), m_min_output_count(0), m_min_output_value(0), m_merge_destinations(false), m_confirm_backlog(true), m_is_initialized(false),m_node_rpc_proxy(m_http_client, m_daemon_rpc_mutex) {}
 
   public:
     static const char* tr(const char* str);
@@ -168,7 +168,20 @@ namespace tools
 
     static bool verify_password(const std::string& keys_file_name, const epee::wipeable_string& password, bool no_spend_key);
 
-    wallet2(bool testnet = false, bool restricted = false) : m_run(true), m_callback(0), m_testnet(testnet), m_always_confirm_transfers(true), m_print_ring_members(false), m_store_tx_info(true), m_default_mixin(0), m_default_priority(0), m_refresh_type(RefreshDefault), m_auto_refresh(true), m_refresh_from_block_height(0), m_confirm_missing_payment_id(true), m_ask_password(true), m_min_output_count(0), m_min_output_value(0), m_merge_destinations(false), m_confirm_backlog(true), m_is_initialized(false), m_restricted(restricted), is_old_file_format(false), m_node_rpc_proxy(m_http_client, m_daemon_rpc_mutex), m_light_wallet(false), m_light_wallet_scanned_block_height(0), m_light_wallet_blockchain_height(0), m_light_wallet_connected(false), m_light_wallet_balance(0), m_light_wallet_unlocked_balance(0) {}
+    wallet2(bool testnet = false, bool restricted = false) : m_multisig_rescan_info(NULL), m_multisig_rescan_k(NULL), m_run(true), m_callback(0), m_testnet(testnet), m_always_confirm_transfers(true), m_print_ring_members(false), m_store_tx_info(true), m_default_mixin(0), m_default_priority(0), m_refresh_type(RefreshDefault), m_auto_refresh(true), m_refresh_from_block_height(0), m_confirm_missing_payment_id(true), m_ask_password(true), m_min_output_count(0), m_min_output_value(0), m_merge_destinations(false), m_confirm_backlog(true), m_is_initialized(false), m_restricted(restricted), is_old_file_format(false), m_node_rpc_proxy(m_http_client, m_daemon_rpc_mutex), m_light_wallet(false), m_light_wallet_scanned_block_height(0), m_light_wallet_blockchain_height(0), m_light_wallet_connected(false), m_light_wallet_balance(0), m_light_wallet_unlocked_balance(0) {}
+
+    struct multisig_info
+    {
+      crypto::key_image m_partial_key_image;
+      rct::key m_L;
+      rct::key m_R;
+
+      BEGIN_SERIALIZE_OBJECT()
+        FIELD(m_partial_key_image)
+        FIELD(m_L)
+        FIELD(m_R)
+      END_SERIALIZE()
+    };
 
     struct tx_scan_info_t
     {
@@ -199,6 +212,9 @@ namespace tools
       bool m_key_image_known;
       size_t m_pk_index;
       cryptonote::subaddress_index m_subaddr_index;
+      bool m_key_image_partial;
+      rct::key m_multisig_k;
+      std::vector<multisig_info> m_multisig_info;
 
       bool is_rct() const { return m_rct; }
       uint64_t amount() const { return m_amount; }
@@ -219,6 +235,9 @@ namespace tools
         FIELD(m_key_image_known)
         FIELD(m_pk_index)
         FIELD(m_subaddr_index)
+        FIELD(m_key_image_partial)
+        FIELD(m_multisig_k)
+        FIELD(m_multisig_info)
       END_SERIALIZE()
     };
 
@@ -322,6 +341,7 @@ namespace tools
       crypto::secret_key tx_key;
       std::vector<crypto::secret_key> additional_tx_keys;
       std::vector<cryptonote::tx_destination_entry> dests;
+      rct::multisig_out msout;
 
       tx_construction_data construction_data;
 
@@ -354,6 +374,12 @@ namespace tools
       std::vector<crypto::key_image> key_images;
     };
 
+    struct multisig_tx_set
+    {
+      std::vector<pending_tx> m_ptx;
+      std::unordered_set<crypto::hash> m_signers;
+    };
+
     struct keys_file_data
     {
       crypto::chacha8_iv iv;
@@ -434,6 +460,16 @@ namespace tools
      */
     static bool verify_multisig_info(const std::string &data, crypto::secret_key &skey, crypto::public_key &pkey);
     /*!
+     * Export multisig info
+     * This will generate and remember new k values
+     */
+    std::vector<tools::wallet2::multisig_info> export_multisig();
+    /*!
+     * Import a set of multisig info from multisig partners
+     * \return the number of inputs which were imported
+     */
+    size_t import_multisig(std::vector<std::vector<tools::wallet2::multisig_info>> info);
+    /*!
      * \brief Rewrites to the wallet file for wallet upgrade (doesn't generate key, assumes it's already there)
      * \param wallet_name Name of wallet file (should exist)
      * \param password    Password for wallet file
@@ -528,6 +564,7 @@ namespace tools
     bool restricted() const { return m_restricted; }
     bool watch_only() const { return m_watch_only; }
     bool multisig(uint32_t *threshold = NULL, uint32_t *total = NULL) const;
+    bool has_multisig_partial_key_images() const;
 
     // locked & unlocked balance of given or current subaddress account
     uint64_t balance(uint32_t subaddr_index_major) const;
@@ -555,6 +592,8 @@ namespace tools
     void commit_tx(pending_tx& ptx_vector);
     void commit_tx(std::vector<pending_tx>& ptx_vector);
     bool save_tx(const std::vector<pending_tx>& ptx_vector, const std::string &filename);
+    bool save_multisig_tx(multisig_tx_set txs, const std::string &filename);
+    bool save_multisig_tx(const std::vector<pending_tx>& ptx_vector, const std::string &filename);
     // load unsigned tx from file and sign it. Takes confirmation callback as argument. Used by the cli wallet
     bool sign_tx(const std::string &unsigned_filename, const std::string &signed_filename, std::vector<wallet2::pending_tx> &ptx, std::function<bool(const unsigned_tx_set&)> accept_func = NULL, bool export_raw = false);
     // sign unsigned tx. Takes unsigned_tx_set as argument. Used by GUI
@@ -567,6 +606,9 @@ namespace tools
     std::vector<wallet2::pending_tx> create_transactions_all(uint64_t below, const cryptonote::account_public_address &address, bool is_subaddress, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, uint32_t subaddr_account, std::set<uint32_t> subaddr_indices, bool trusted_daemon);
     std::vector<wallet2::pending_tx> create_transactions_single(const crypto::key_image &ki, const cryptonote::account_public_address &address, bool is_subaddress, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, bool trusted_daemon);
     std::vector<wallet2::pending_tx> create_transactions_from(const cryptonote::account_public_address &address, bool is_subaddress, std::vector<size_t> unused_transfers_indices, std::vector<size_t> unused_dust_indices, const size_t fake_outs_count, const uint64_t unlock_time, uint32_t priority, const std::vector<uint8_t>& extra, bool trusted_daemon);
+    bool load_multisig_tx_from_file(const std::string &filename, multisig_tx_set &exported_txs, std::function<bool(const multisig_tx_set&)> accept_func = NULL);
+    bool sign_multisig_tx_from_file(const std::string &filename, std::vector<crypto::hash> &txids, std::function<bool(const multisig_tx_set&)> accept_func);
+    bool sign_multisig_tx(multisig_tx_set &exported_txs, const std::string &filename, std::vector<crypto::hash> &txids);
     std::vector<pending_tx> create_unmixable_sweep_transactions(bool trusted_daemon);
     bool check_connection(uint32_t *version = NULL, uint32_t timeout = 200000);
     void get_transfers(wallet2::transfer_container& incoming_transfers) const;
@@ -881,7 +923,6 @@ namespace tools
     void check_genesis(const crypto::hash& genesis_hash) const; //throws
     bool generate_chacha8_key_from_secret_keys(crypto::chacha8_key &key) const;
     crypto::hash get_payment_id(const pending_tx &ptx) const;
-    crypto::hash8 get_short_payment_id(const pending_tx &ptx) const;
     void check_acc_out_precomp(const cryptonote::tx_out &o, const crypto::key_derivation &derivation, const std::vector<crypto::key_derivation> &additional_derivations, size_t i, tx_scan_info_t &tx_scan_info) const;
     void parse_block_round(const cryptonote::blobdata &blob, cryptonote::block &bl, crypto::hash &bl_id, bool &error) const;
     uint64_t get_upper_transaction_size_limit();
@@ -893,12 +934,15 @@ namespace tools
     void set_unspent(size_t idx);
     void get_outs(std::vector<std::vector<get_outs_entry>> &outs, const std::vector<size_t> &selected_transfers, size_t fake_outputs_count);
     bool tx_add_fake_output(std::vector<std::vector<tools::wallet2::get_outs_entry>> &outs, uint64_t global_index, const crypto::public_key& tx_public_key, const rct::key& mask, uint64_t real_index, bool unlocked) const;
-    bool wallet_generate_key_image_helper(const cryptonote::account_keys& ack, const crypto::public_key& tx_public_key, size_t real_output_index, cryptonote::keypair& in_ephemeral, crypto::key_image& ki);
     crypto::public_key get_tx_pub_key_from_received_outs(const tools::wallet2::transfer_details &td) const;
     bool should_pick_a_second_output(bool use_rct, size_t n_transfers, const std::vector<size_t> &unused_transfers_indices, const std::vector<size_t> &unused_dust_indices) const;
     std::vector<size_t> get_only_rct(const std::vector<size_t> &unused_dust_indices, const std::vector<size_t> &unused_transfers_indices) const;
     void scan_output(const cryptonote::account_keys &keys, const cryptonote::transaction &tx, const crypto::public_key &tx_pub_key, size_t i, tx_scan_info_t &tx_scan_info, int &num_vouts_received, std::unordered_map<cryptonote::subaddress_index, uint64_t> &tx_money_got_in_outs, std::vector<size_t> &outs);
     void trim_hashchain();
+    rct::multisig_kLRki get_multisig_composite_LRki(size_t n, const rct::key &k) const;
+    rct::multisig_kLRki get_multisig_LRki(size_t n, const rct::key &k) const;
+    rct::key get_multisig_k(size_t idx) const;
+    void update_multisig_rescan_info(const std::vector<rct::key> &multisig_k, const std::vector<std::vector<tools::wallet2::multisig_info>> &info, size_t n);
 
     cryptonote::account_base m_account;
     boost::optional<epee::net_utils::http::login> m_daemon_login;
@@ -927,6 +971,8 @@ namespace tools
     std::unordered_map<std::string, std::string> m_attributes;
     std::vector<tools::wallet2::address_book_row> m_address_book;
     uint64_t m_upper_transaction_size_limit; //TODO: auto-calc this value or request from daemon, now use some fixed value
+    const std::vector<std::vector<tools::wallet2::multisig_info>> *m_multisig_rescan_info;
+    const std::vector<rct::key> *m_multisig_rescan_k;
 
     std::atomic<bool> m_run;
 
@@ -976,7 +1022,9 @@ namespace tools
   };
 }
 BOOST_CLASS_VERSION(tools::wallet2, 22)
-BOOST_CLASS_VERSION(tools::wallet2::transfer_details, 8)
+BOOST_CLASS_VERSION(tools::wallet2::transfer_details, 9)
+BOOST_CLASS_VERSION(tools::wallet2::multisig_info, 1)
+BOOST_CLASS_VERSION(tools::wallet2::multisig_tx_set, 1)
 BOOST_CLASS_VERSION(tools::wallet2::payment_details, 2)
 BOOST_CLASS_VERSION(tools::wallet2::pool_payment_details, 1)
 BOOST_CLASS_VERSION(tools::wallet2::unconfirmed_transfer_details, 7)
@@ -985,7 +1033,7 @@ BOOST_CLASS_VERSION(tools::wallet2::address_book_row, 17)
 BOOST_CLASS_VERSION(tools::wallet2::unsigned_tx_set, 0)
 BOOST_CLASS_VERSION(tools::wallet2::signed_tx_set, 0)
 BOOST_CLASS_VERSION(tools::wallet2::tx_construction_data, 2)
-BOOST_CLASS_VERSION(tools::wallet2::pending_tx, 2)
+BOOST_CLASS_VERSION(tools::wallet2::pending_tx, 3)
 
 namespace boost
 {
@@ -1023,6 +1071,12 @@ namespace boost
         {
           x.m_subaddr_index = {};
         }
+        if (ver < 9)
+        {
+          x.m_key_image_partial = false;
+          x.m_multisig_info.clear();
+          x.m_multisig_k = rct::zero();
+        }
     }
 
     template <class Archive>
@@ -1096,6 +1150,29 @@ namespace boost
         return;
       }
       a & x.m_subaddr_index;
+      if (ver < 9)
+      {
+        initialize_transfer_details(a, x, ver);
+        return;
+      }
+      a & x.m_multisig_info;
+      a & x.m_multisig_k;
+      a & x.m_key_image_partial;
+    }
+
+    template <class Archive>
+    inline void serialize(Archive &a, tools::wallet2::multisig_info &x, const boost::serialization::version_type ver)
+    {
+      a & x.m_partial_key_image;
+      a & x.m_L;
+      a & x.m_R;
+    }
+
+    template <class Archive>
+    inline void serialize(Archive &a, tools::wallet2::multisig_tx_set &x, const boost::serialization::version_type ver)
+    {
+      a & x.m_ptx;
+      a & x.m_signers;
     }
 
     template <class Archive>
@@ -1301,6 +1378,9 @@ namespace boost
       if (ver < 2)
         return;
       a & x.selected_transfers;
+      if (ver < 3)
+        return;
+      a & x.msout;
     }
   }
 }
@@ -1478,6 +1558,10 @@ namespace tools
       src.real_out_tx_key = get_tx_pub_key_from_extra(td.m_tx);
       src.real_output = interted_it - src.outputs.begin();
       src.real_output_in_tx_index = td.m_internal_output_index;
+      if (m_multisig)
+        src.multisig_kLRki = get_multisig_composite_LRki(idx, get_multisig_k(idx));
+      else
+        src.multisig_kLRki = rct::multisig_kLRki({rct::zero(), rct::zero(), rct::zero(), rct::zero()});
       detail::print_source_entry(src);
       ++i;
     }
@@ -1504,7 +1588,8 @@ namespace tools
 
     crypto::secret_key tx_key;
     std::vector<crypto::secret_key> additional_tx_keys;
-    bool r = cryptonote::construct_tx_and_get_tx_key(m_account.get_keys(), m_subaddresses, sources, splitted_dsts, change_dts.addr, extra, tx, unlock_time, tx_key, additional_tx_keys);
+    rct::multisig_out msout;
+    bool r = cryptonote::construct_tx_and_get_tx_key(m_account.get_keys(), m_subaddresses, sources, splitted_dsts, change_dts.addr, extra, tx, unlock_time, tx_key, additional_tx_keys, false, false, m_multisig ? &msout : NULL);
     THROW_WALLET_EXCEPTION_IF(!r, error::tx_not_constructed, sources, splitted_dsts, unlock_time, m_testnet);
     THROW_WALLET_EXCEPTION_IF(upper_transaction_size_limit <= get_object_blobsize(tx), error::tx_too_big, tx, upper_transaction_size_limit);
 
@@ -1532,6 +1617,7 @@ namespace tools
     ptx.tx_key = tx_key;
     ptx.additional_tx_keys = additional_tx_keys;
     ptx.dests = dsts;
+    ptx.msout = msout;
     ptx.construction_data.sources = sources;
     ptx.construction_data.change_dts = change_dts;
     ptx.construction_data.splitted_dsts = splitted_dsts;