Match surae's recommendation to derive multisig keys

5 files changed, 43 insertions, 33 deletions

diff --git a/src/multisig/multisig.cpp b/src/multisig/multisig.cpp
index a99f66e64..39d0e1c4b 100644
--- a/src/multisig/multisig.cpp
+++ b/src/multisig/multisig.cpp
@@ -39,18 +39,29 @@
 
 using namespace std;
 
+static const rct::key multisig_salt = { {'M', 'u', 'l', 't' , 'i', 's', 'i', 'g', 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } };
+
 namespace cryptonote
 {
   //-----------------------------------------------------------------
+  crypto::secret_key get_multisig_blinded_secret_key(const crypto::secret_key &key)
+  {
+    rct::keyV data;
+    data.push_back(rct::sk2rct(key));
+    data.push_back(multisig_salt);
+    return rct::rct2sk(rct::hash_to_scalar(data));
+  }
+  //-----------------------------------------------------------------
   void generate_multisig_N_N(const account_keys &keys, const std::vector<crypto::public_key> &spend_keys, std::vector<crypto::secret_key> &multisig_keys, rct::key &spend_skey, rct::key &spend_pkey)
   {
     // the multisig spend public key is the sum of all spend public keys
     multisig_keys.clear();
-    spend_pkey = rct::pk2rct(keys.m_account_address.m_spend_public_key);
+    const crypto::secret_key spend_secret_key = get_multisig_blinded_secret_key(keys.m_spend_secret_key);
+    CHECK_AND_ASSERT_THROW_MES(crypto::secret_key_to_public_key(spend_secret_key, (crypto::public_key&)spend_pkey), "Failed to derive public key");
     for (const auto &k: spend_keys)
       rct::addKeys(spend_pkey, spend_pkey, rct::pk2rct(k));
-    multisig_keys.push_back(keys.m_spend_secret_key);
-    spend_skey = rct::sk2rct(keys.m_spend_secret_key);
+    multisig_keys.push_back(spend_secret_key);
+    spend_skey = rct::sk2rct(spend_secret_key);
   }
   //-----------------------------------------------------------------
   void generate_multisig_N1_N(const account_keys &keys, const std::vector<crypto::public_key> &spend_keys, std::vector<crypto::secret_key> &multisig_keys, rct::key &spend_skey, rct::key &spend_pkey)
@@ -60,23 +71,19 @@ namespace cryptonote
     spend_skey = rct::zero();
 
     // create all our composite private keys
+    crypto::secret_key blinded_skey = get_multisig_blinded_secret_key(keys.m_spend_secret_key);
     for (const auto &k: spend_keys)
     {
-      rct::keyV data;
-      data.push_back(rct::scalarmultKey(rct::pk2rct(k), rct::sk2rct(keys.m_spend_secret_key)));
-      static const rct::key salt = { {'M', 'u', 'l', 't' , 'i', 's', 'i', 'g' , 0x00, 0x00, 0x00,0x00 , 0x00, 0x00, 0x00,0x00 , 0x00, 0x00, 0x00,0x00 , 0x00, 0x00, 0x00,0x00 , 0x00, 0x00, 0x00,0x00 , 0x00, 0x00, 0x00,0x00  } };
-      data.push_back(salt);
-      rct::key msk = rct::hash_to_scalar(data);
-      multisig_keys.push_back(rct::rct2sk(msk));
-      sc_add(spend_skey.bytes, spend_skey.bytes, msk.bytes);
+      rct::key sk = rct::scalarmultKey(rct::pk2rct(k), rct::sk2rct(blinded_skey));
+      crypto::secret_key msk = get_multisig_blinded_secret_key(rct::rct2sk(sk));
+      multisig_keys.push_back(msk);
+      sc_add(spend_skey.bytes, spend_skey.bytes, (const unsigned char*)msk.data);
     }
   }
   //-----------------------------------------------------------------
   crypto::secret_key generate_multisig_view_secret_key(const crypto::secret_key &skey, const std::vector<crypto::secret_key> &skeys)
   {
-    crypto::hash hash;
-    crypto::cn_fast_hash(&skey, sizeof(crypto::hash), hash);
-    rct::key view_skey = rct::hash2rct(hash);
+    rct::key view_skey = rct::sk2rct(get_multisig_blinded_secret_key(skey));
     for (const auto &k: skeys)
       sc_add(view_skey.bytes, view_skey.bytes, rct::sk2rct(k).bytes);
     return rct::rct2sk(view_skey);
diff --git a/src/multisig/multisig.h b/src/multisig/multisig.h
index 5cb469c1b..f29b47987 100644
--- a/src/multisig/multisig.h
+++ b/src/multisig/multisig.h
@@ -38,6 +38,7 @@ namespace cryptonote
 {
   struct account_keys;
 
+  crypto::secret_key get_multisig_blinded_secret_key(const crypto::secret_key &key);
   void generate_multisig_N_N(const account_keys &keys, const std::vector<crypto::public_key> &spend_keys, std::vector<crypto::secret_key> &multisig_keys, rct::key &spend_skey, rct::key &spend_pkey);
   void generate_multisig_N1_N(const account_keys &keys, const std::vector<crypto::public_key> &spend_keys, std::vector<crypto::secret_key> &multisig_keys, rct::key &spend_skey, rct::key &spend_pkey);
   crypto::secret_key generate_multisig_view_secret_key(const crypto::secret_key &skey, const std::vector<crypto::secret_key> &skeys);
diff --git a/src/simplewallet/simplewallet.cpp b/src/simplewallet/simplewallet.cpp
index 98d7ea14f..145d90d91 100644
--- a/src/simplewallet/simplewallet.cpp
+++ b/src/simplewallet/simplewallet.cpp
@@ -60,6 +60,7 @@
 #include "rapidjson/document.h"
 #include "common/json_util.h"
 #include "ringct/rctSigs.h"
+#include "multisig/multisig.h"
 #include "wallet/wallet_args.h"
 #include <stdexcept>
 
@@ -801,8 +802,8 @@ bool simple_wallet::make_multisig(const std::vector<std::string> &args)
   }
 
   // people may include their own, weed it out
-  const crypto::secret_key local_skey = m_wallet->get_account().get_keys().m_view_secret_key;
-  const crypto::public_key local_pkey = m_wallet->get_account().get_keys().m_account_address.m_spend_public_key;
+  const crypto::secret_key local_skey = cryptonote::get_multisig_blinded_secret_key(m_wallet->get_account().get_keys().m_view_secret_key);
+  const crypto::public_key local_pkey = m_wallet->get_multisig_signer_public_key(m_wallet->get_account().get_keys().m_spend_secret_key);
   for (size_t i = 0; i < secret_keys.size(); ++i)
   {
     if (secret_keys[i] == local_skey)
diff --git a/src/wallet/wallet2.cpp b/src/wallet/wallet2.cpp
index 013ad6a75..29ca3dd2f 100644
--- a/src/wallet/wallet2.cpp
+++ b/src/wallet/wallet2.cpp
@@ -2830,8 +2830,6 @@ std::string wallet2::make_multisig(const epee::wipeable_string &password,
     // We need an extra step, so we package all the composite public keys
     // we know about, and make a signed string out of them
     std::string data;
-    const crypto::public_key &pkey = get_account().get_keys().m_account_address.m_spend_public_key;
-    data += std::string((const char *)&pkey, sizeof(crypto::public_key));
     const crypto::public_key signer = get_multisig_signer_public_key(rct::rct2sk(spend_skey));
     data += std::string((const char *)&signer, sizeof(crypto::public_key));
 
@@ -2844,7 +2842,7 @@ std::string wallet2::make_multisig(const epee::wipeable_string &password,
     data.resize(data.size() + sizeof(crypto::signature));
     crypto::cn_fast_hash(data.data(), data.size() - sizeof(signature), hash);
     crypto::signature &signature = *(crypto::signature*)&data[data.size() - sizeof(crypto::signature)];
-    crypto::generate_signature(hash, pkey, get_account().get_keys().m_spend_secret_key, signature);
+    crypto::generate_signature(hash, signer, get_multisig_blinded_secret_key(rct::rct2sk(spend_skey)), signature);
 
     extra_multisig_info = std::string("MultisigxV1") + tools::base58::encode(data);
   }
@@ -2958,19 +2956,18 @@ bool wallet2::finalize_multisig(const epee::wipeable_string &password, const std
 std::string wallet2::get_multisig_info() const
 {
   // It's a signed package of private view key and public spend key
-  const crypto::secret_key &skey = get_account().get_keys().m_view_secret_key;
-  const crypto::public_key &pkey = get_account().get_keys().m_account_address.m_spend_public_key;
+  const crypto::secret_key skey = cryptonote::get_multisig_blinded_secret_key(get_account().get_keys().m_view_secret_key);
+  const crypto::public_key pkey = get_multisig_signer_public_key(get_account().get_keys().m_spend_secret_key);
   crypto::hash hash;
 
   std::string data;
-  crypto::cn_fast_hash(&skey, sizeof(crypto::secret_key), hash);
-  data += std::string((const char *)&hash, sizeof(crypto::hash));
+  data += std::string((const char *)&skey, sizeof(crypto::secret_key));
   data += std::string((const char *)&pkey, sizeof(crypto::public_key));
 
   data.resize(data.size() + sizeof(crypto::signature));
   crypto::cn_fast_hash(data.data(), data.size() - sizeof(signature), hash);
   crypto::signature &signature = *(crypto::signature*)&data[data.size() - sizeof(crypto::signature)];
-  crypto::generate_signature(hash, pkey, get_account().get_keys().m_spend_secret_key, signature);
+  crypto::generate_signature(hash, pkey, get_multisig_blinded_secret_key(get_account().get_keys().m_spend_secret_key), signature);
 
   return std::string("MultisigV1") + tools::base58::encode(data);
 }
@@ -3027,28 +3024,26 @@ bool wallet2::verify_extra_multisig_info(const std::string &data, std::unordered
     MERROR("Multisig info decoding error");
     return false;
   }
-  if (decoded.size() < sizeof(crypto::public_key) + sizeof(crypto::public_key) + sizeof(crypto::signature))
+  if (decoded.size() < sizeof(crypto::public_key) + sizeof(crypto::signature))
   {
     MERROR("Multisig info is corrupt");
     return false;
   }
-  if ((decoded.size() - (sizeof(crypto::public_key) + sizeof(crypto::public_key) + sizeof(crypto::signature))) % sizeof(crypto::public_key))
+  if ((decoded.size() - (sizeof(crypto::public_key) + sizeof(crypto::signature))) % sizeof(crypto::public_key))
   {
     MERROR("Multisig info is corrupt");
     return false;
   }
 
-  const size_t n_keys = (decoded.size() - (sizeof(crypto::public_key) + sizeof(crypto::public_key) + sizeof(crypto::signature))) / sizeof(crypto::public_key);
+  const size_t n_keys = (decoded.size() - (sizeof(crypto::public_key) + sizeof(crypto::signature))) / sizeof(crypto::public_key);
   size_t offset = 0;
-  const crypto::public_key &pkey = *(const crypto::public_key*)(decoded.data() + offset);
-  offset += sizeof(pkey);
   signer = *(const crypto::public_key*)(decoded.data() + offset);
   offset += sizeof(signer);
   const crypto::signature &signature = *(const crypto::signature*)(decoded.data() + offset + n_keys * sizeof(crypto::public_key));
 
   crypto::hash hash;
   crypto::cn_fast_hash(decoded.data(), decoded.size() - sizeof(signature), hash);
-  if (!crypto::check_signature(hash, pkey, signature))
+  if (!crypto::check_signature(hash, signer, signature))
   {
     MERROR("Multisig info signature is invalid");
     return false;
@@ -8313,13 +8308,19 @@ size_t wallet2::import_outputs(const std::vector<tools::wallet2::transfer_detail
 crypto::public_key wallet2::get_multisig_signer_public_key(const crypto::secret_key &spend_skey) const
 {
   crypto::public_key pkey;
-  crypto::secret_key_to_public_key(spend_skey, pkey);
+  crypto::secret_key_to_public_key(get_multisig_blinded_secret_key(spend_skey), pkey);
   return pkey;
 }
 //----------------------------------------------------------------------------------------------------
 crypto::public_key wallet2::get_multisig_signer_public_key() const
 {
   CHECK_AND_ASSERT_THROW_MES(m_multisig, "Wallet is not multisig");
+  if (m_multisig_threshold == m_multisig_signers.size())
+  {
+    crypto::public_key signer;
+    CHECK_AND_ASSERT_THROW_MES(crypto::secret_key_to_public_key(get_account().get_keys().m_spend_secret_key, signer), "Failed to generate signer public key");
+    return signer;
+  }
   return get_multisig_signer_public_key(get_account().get_keys().m_spend_secret_key);
 }
 //----------------------------------------------------------------------------------------------------
diff --git a/src/wallet/wallet_rpc_server.cpp b/src/wallet/wallet_rpc_server.cpp
index 043890fd1..e6e5445b2 100644
--- a/src/wallet/wallet_rpc_server.cpp
+++ b/src/wallet/wallet_rpc_server.cpp
@@ -41,6 +41,7 @@ using namespace epee;
 #include "common/i18n.h"
 #include "cryptonote_basic/cryptonote_format_utils.h"
 #include "cryptonote_basic/account.h"
+#include "multisig/multisig.h"
 #include "wallet_rpc_server_commands_defs.h"
 #include "misc_language.h"
 #include "string_coding.h"
@@ -2424,11 +2425,10 @@ namespace tools
     }
 
     // people may include their own, weed it out
-    crypto::hash hash;
-    crypto::cn_fast_hash(&m_wallet->get_account().get_keys().m_view_secret_key, sizeof(crypto::secret_key), hash);
+    crypto::secret_key local_skey = cryptonote::get_multisig_blinded_secret_key(m_wallet->get_account().get_keys().m_view_secret_key);
     for (size_t i = 0; i < secret_keys.size(); ++i)
     {
-      if (rct::sk2rct(secret_keys[i]) == rct::hash2rct(hash))
+      if (rct::sk2rct(secret_keys[i]) == rct::sk2rct(local_skey))
       {
         secret_keys[i] = secret_keys.back();
         public_keys[i] = public_keys.back();