通过以前的一些文章，我们知道Bitshares中operation都需要签名，也了解到签名一般都使用公私钥，看起来Bitshares签名有不少代码，到底都做了些什么呢？

对公私钥有兴趣的请google非对称加密、RSA、公私钥等

需要的签名公钥

在operation函数最后，一般都会调用

      return sign_transaction( tx, broadcast );

看看sign_transaction()函数：

   signed_transaction sign_transaction(signed_transaction tx, bool broadcast = false)
   {
      set<public_key_type> pks = _remote_db->get_potential_signatures( tx );
      flat_set<public_key_type> owned_keys;
      owned_keys.reserve( pks.size() );
      std::copy_if( pks.begin(), pks.end(), std::inserter(owned_keys, owned_keys.end()),
                    [this](const public_key_type& pk){ return _keys.find(pk) != _keys.end(); } );
      set<public_key_type> approving_key_set = _remote_db->get_required_signatures( tx, owned_keys );

      auto dyn_props = get_dynamic_global_properties();
      tx.set_reference_block( dyn_props.head_block_id );

      // first, some bookkeeping, expire old items from _recently_generated_transactions
      // since transactions include the head block id, we just need the index for keeping transactions unique
      // when there are multiple transactions in the same block.  choose a time period that should be at
      // least one block long, even in the worst case.  2 minutes ought to be plenty.
      fc::time_point_sec oldest_transaction_ids_to_track(dyn_props.time - fc::minutes(2));
      auto oldest_transaction_record_iter = _recently_generated_transactions.get<timestamp_index>().lower_bound(oldest_transaction_ids_to_track);
      auto begin_iter = _recently_generated_transactions.get<timestamp_index>().begin();
      _recently_generated_transactions.get<timestamp_index>().erase(begin_iter, oldest_transaction_record_iter);

      uint32_t expiration_time_offset = 0;
      for (;;)
      {
         tx.set_expiration( dyn_props.time + fc::seconds(30 + expiration_time_offset) );
         tx.signatures.clear();

         for( const public_key_type& key : approving_key_set )
            tx.sign( get_private_key(key), _chain_id );

         graphene::chain::transaction_id_type this_transaction_id = tx.id();
         auto iter = _recently_generated_transactions.find(this_transaction_id);
         if (iter == _recently_generated_transactions.end())
         {
            // we haven't generated this transaction before, the usual case
            recently_generated_transaction_record this_transaction_record;
            this_transaction_record.generation_time = dyn_props.time;
            this_transaction_record.transaction_id = this_transaction_id;
            _recently_generated_transactions.insert(this_transaction_record);
            break;
         }

         // else we've generated a dupe, increment expiration time and re-sign it
         ++expiration_time_offset;
      }
      ...
      return tx;
   }

看起来是通过 get_potential_signatures() 函数先取到可能的公钥，然后再通过 get_required_signatures() 取到需要签名的公钥，再填充交易块信息等签名后发送。

没明白怎么通过交易取到可能的签名公钥，继续看下这个函数：

set<public_key_type> database_api_impl::get_potential_signatures( const signed_transaction& trx )const
{
   set<public_key_type> result;
   trx.get_required_signatures(
      _db.get_chain_id(),
      flat_set<public_key_type>(),
      [&]( account_id_type id )
      {
         const auto& auth = id(_db).active;
         for( const auto& k : auth.get_keys() )
            result.insert(k);
         return &auth;
      },
      [&]( account_id_type id )
      {
         const auto& auth = id(_db).owner;
         for( const auto& k : auth.get_keys() )
            result.insert(k);
         return &auth;
      },
      _db.get_global_properties().parameters.max_authority_depth
   );

   // Insert keys in required "other" authories
   flat_set<account_id_type> required_active;
   flat_set<account_id_type> required_owner;
   vector<authority> other;
   trx.get_required_authorities( required_active, required_owner, other );
   for( const auto& auth : other )
      for( const auto& key : auth.get_keys() )
         result.insert( key );

   return result;
}

函数内部又调用交易的 get_required_signatures() 函数：

set<public_key_type> signed_transaction::get_required_signatures(
   const chain_id_type& chain_id,
   const flat_set<public_key_type>& available_keys,
   const std::function<const authority*(account_id_type)>& get_active,
   const std::function<const authority*(account_id_type)>& get_owner,
   uint32_t max_recursion_depth )const
{
   flat_set<account_id_type> required_active;
   flat_set<account_id_type> required_owner;
   vector<authority> other;
   get_required_authorities( required_active, required_owner, other );

   flat_set<public_key_type> signature_keys = get_signature_keys( chain_id );
   sign_state s( signature_keys, get_active, available_keys );
   s.max_recursion = max_recursion_depth;

   for( const auto& auth : other )
      s.check_authority(&auth);
   for( auto& owner : required_owner )
      s.check_authority( get_owner( owner ) );
   for( auto& active : required_active )
      s.check_authority( active ) || s.check_authority( get_owner( active ) );

   s.remove_unused_signatures();

   set<public_key_type> result;

   for( auto& provided_sig : s.provided_signatures )
      if( available_keys.find( provided_sig.first ) != available_keys.end()
            && signature_keys.find( provided_sig.first ) == signature_keys.end() )
         result.insert( provided_sig.first );

   return result;
}

get_required_signatures函数有5个参数：链id、公钥set、get_active函数、get_owner函数、最大深度。

sign_state 用来存储签名状态，构造函数传入3个参数：已签名key、get_active函数、有效keys。这个函数后面一部分都是使用sign_state对象处理逻辑。

check_authority()函数可以判断出是否已有足够的key签名。

又会调用到 get_required_authorities() 函数，而此函数内部通过调用 operation_get_required_authorities() 得到需要的认证key。

void transaction::get_required_authorities( flat_set<account_id_type>& active, flat_set<account_id_type>& owner, vector<authority>& other )const
{
   for( const auto& op : operations )
      operation_get_required_authorities( op, active, owner, other );
   for( const auto& account : owner )
      active.erase( account );
}

void operation_get_required_authorities( const operation& op, 
                                         flat_set<account_id_type>& active,
                                         flat_set<account_id_type>& owner,
                                         vector<authority>&  other )
{
   op.visit( operation_get_required_auth( active, owner, other ) );
}

当前交易所带的operations必须大于0个，怎么通过 operation_get_required_authorities() 取得需要的认证key？

operation_get_required_auth 是一个如下的类定义：

struct operation_get_required_auth
{
   typedef void result_type;

   flat_set<account_id_type>& active;
   flat_set<account_id_type>& owner;
   vector<authority>&         other;


   operation_get_required_auth( flat_set<account_id_type>& a,
     flat_set<account_id_type>& own,
     vector<authority>&  oth ):active(a),owner(own),other(oth){}

   template<typename T>
   void operator()( const T& v )const 
   { 
      active.insert( v.fee_payer() );
      v.get_required_active_authorities( active ); 
      v.get_required_owner_authorities( owner ); 
      v.get_required_authorities( other );
   }
};

此处的v就是一个operation，active key会插入每个operation的fee_payer，这个fee_payer()函数是每个operation单独定义的。

从代码中看get_required_xxx也只有account_create_operation、account_update_operation、proposal_update_operation等少数几个operation有单独的处理，而缺省的operation并没有什么操作。那就是一般情况下，active key中会有操作的付费帐号。

operation特别指定

get_required_active_authorities

get_required_owner_authorities

account_update_operation，更新owner key时需要owner权限：

      void get_required_owner_authorities( flat_set<account_id_type>& a )const
      { if( is_owner_update() ) a.insert( account ); }

      void get_required_active_authorities( flat_set<account_id_type>& a )const
      { if( !is_owner_update() ) a.insert( account ); }      

proposal_update_operation，需要提议审批人的权限：

void proposal_update_operation::get_required_active_authorities( flat_set<account_id_type>& a )const
{
   for( const auto& i : active_approvals_to_add )    a.insert(i);
   for( const auto& i : active_approvals_to_remove ) a.insert(i);
}

void proposal_update_operation::get_required_owner_authorities( flat_set<account_id_type>& a )const
{
   for( const auto& i : owner_approvals_to_add )    a.insert(i);
   for( const auto& i : owner_approvals_to_remove ) a.insert(i);
}

get_required_authorities

get_required_authorities在 get_required_authorities、transfer_from_blind_operation、blind_transfer_operation、proposal_update_operation有单独的处理，来看下proposal_update_operation这块认证权限的指定：

void proposal_update_operation::get_required_authorities( vector<authority>& o )const
{
   authority auth;
   for( const auto& k : key_approvals_to_add )
      auth.key_auths[k] = 1;
   for( const auto& k : key_approvals_to_remove )
      auth.key_auths[k] = 1;
   auth.weight_threshold = auth.key_auths.size();

   o.emplace_back( std::move(auth) );
}

上面代码实现了提议的多重签名功能，weight_threshold指定了需要auth.key_auths指定的所有人同意提议。

签名

交易签名比较简单，用私钥生成签名后加到signatures就完事了，如下：

const signature_type& graphene::chain::signed_transaction::sign(const private_key_type& key, const chain_id_type& chain_id)
{
   digest_type h = sig_digest( chain_id );
   signatures.push_back(key.sign_compact(h));
   return signatures.back();
}

elliptic_impl_priv.cpp

    compact_signature private_key::sign_compact( const fc::sha256& digest, bool require_canonical )const
    {
        FC_ASSERT( my->_key != empty_priv );
        compact_signature result;
        int recid;
        unsigned int counter = 0;
        do
        {
            FC_ASSERT( secp256k1_ecdsa_sign_compact( detail::_get_context(), (unsigned char*) digest.data(), (unsigned char*) result.begin() + 1, (unsigned char*) my->_key.data(), extended_nonce_function, &counter, &recid ));
        } while( require_canonical && !public_key::is_canonical( result ) );
        result.begin()[0] = 27 + 4 + recid;
        return result;
    }

验证签名

void verify_authority( const vector<operation>& ops, const flat_set<public_key_type>& sigs, 
                       const std::function<const authority*(account_id_type)>& get_active,
                       const std::function<const authority*(account_id_type)>& get_owner,
                       uint32_t max_recursion_depth,
                       bool  allow_committe,
                       const flat_set<account_id_type>& active_aprovals,
                       const flat_set<account_id_type>& owner_approvals )
{ try {
   flat_set<account_id_type> required_active;
   flat_set<account_id_type> required_owner;
   vector<authority> other;

   for( const auto& op : ops )
      operation_get_required_authorities( op, required_active, required_owner, other );

   if( !allow_committe )
      GRAPHENE_ASSERT( required_active.find(GRAPHENE_COMMITTEE_ACCOUNT) == required_active.end(),
                       invalid_committee_approval, "Committee account may only propose transactions" );

   sign_state s(sigs,get_active);
   s.max_recursion = max_recursion_depth;
   for( auto& id : active_aprovals )
      s.approved_by.insert( id );
   for( auto& id : owner_approvals )
      s.approved_by.insert( id );

   for( const auto& auth : other )
   {
      GRAPHENE_ASSERT( s.check_authority(&auth), tx_missing_other_auth, "Missing Authority", ("auth",auth)("sigs",sigs) );
   }

   // fetch all of the top level authorities
   for( auto id : required_active )
   {
      GRAPHENE_ASSERT( s.check_authority(id) || 
                       s.check_authority(get_owner(id)), 
                       tx_missing_active_auth, "Missing Active Authority ${id}", ("id",id)("auth",*get_active(id))("owner",*get_owner(id)) );
   }

   for( auto id : required_owner )
   {
      GRAPHENE_ASSERT( owner_approvals.find(id) != owner_approvals.end() ||
                       s.check_authority(get_owner(id)), 
                       tx_missing_owner_auth, "Missing Owner Authority ${id}", ("id",id)("auth",*get_owner(id)) );
   }

   GRAPHENE_ASSERT(
      !s.remove_unused_signatures(),
      tx_irrelevant_sig,
      "Unnecessary signature(s) detected"
      );
} FC_CAPTURE_AND_RETHROW( (ops)(sigs) ) }

verify_authority函数中调用的其它函数在上面已经分析过了，就是判断需要哪些密钥签名和已经有哪些有效的签名。

这个函数在处理每笔交易时调用，如下：

processed_transaction database::_apply_transaction(const signed_transaction& trx)
{
   ...
   if( !(skip & (skip_transaction_signatures | skip_authority_check) ) )
   {
      auto get_active = [&]( account_id_type id ) { return &id(*this).active; };
      auto get_owner  = [&]( account_id_type id ) { return &id(*this).owner;  };
      trx.verify_authority( chain_id, get_active, get_owner, get_global_properties().parameters.max_authority_depth );
   }

结论

交易签名首先会需要operation指定的支付人的签名，对一些特殊的operation可能还需要其他帐户签名，如提议等。

简单过了一下权限签名相关的代码，下次再碰到“Missing Authority”提示时就容易了解和解决问题了。

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