Properly implement spam signing and checking to prevent it from been used to impersonate users.

"nobody" is an exception so default client could still send unauthenticated/anonymous spam
messages.

TODO

@@ -66,10 +66,6 @@ of his own torrent)
 - Estimate number of online followers by quering the "tracker" resource (implement a value within
 this resource to report the number of torrent peers)
 
-- Properly implement spam signing and checking to prevent it from been used to impersonate users.
-"nobody" might be an exception so default client could still send unauthenticated/anonymous spam
-messages.
-
 - Define and enforce html directory to serve from. Do installation scripts.
 
 - Don't accept dht "post"+k if k violates the validatePostNumberForUser() rule.

src/bitcoind.cpp

@@ -124,64 +124,6 @@ bool AppInit(int argc, char* argv[])
 }
 
 
-static const string strSecret1C    ("Kwr371tjA9u2rFSMZjTNun2PXXP3WPZu2afRHTcta6KxEUdm1vEw");
-
-static bool TestCreateSpamMsgTx()
-{
-    CTransaction txNew;
-
-    txNew.message = CScript() << strSpamMessage;
-
-    CBitcoinSecret bsecret1;
-    bsecret1.SetString (strSecret1C);
-
-    CKey key;
-    key.MakeNewKey(true);
-    //CKey key =  bsecret1.GetKey();
-    CPubKey pubkey( key.GetPubKey() );
-
-    printf("key valid: %d compressed: %d\n", key.IsValid(), key.IsCompressed());
-    printf("pubkey: %s\n", EncodeBase64(&pubkey[0], pubkey.size()).c_str() );
-
-    // compute message hash and sign it
-    CHashWriter ss(SER_GETHASH, PROTOCOL_VERSION);
-    ss << txNew.message;
-    uint256 hashMsg = ss.GetHash();
-
-    // vchSig is sig(hash(message))
-    vector<unsigned char> vchSig;
-    if (!key.Sign(hashMsg, vchSig)) {
-        printf("CreateNewBlock: Failed to sign SpamMessage\n");
-        return false;
-    }
-
-    /*
-    vector<unsigned char> vchSigCompact;
-    if (!key.SignCompact(hashMsg, vchSigCompact)) {
-        printf("CreateNewBlock: Failed to sign SpamMessage2\n");
-        return false;
-    }
-    printf("sign size: %zu signCompact size: %zu\n", vchSig.size(), vchSigCompact.size());
-    printf("signCompact: %s\n", EncodeBase64(&vchSigCompact[0], vchSigCompact.size()).c_str());
-    */
-
-    printf("CreateSpamMsgTx: msg = %s user = %s hash = %s signedhash = %s\n", txNew.message.ToString().c_str(), strSpamUser.c_str(),
-           hashMsg.ToString().c_str(), EncodeBase64(&vchSig[0], vchSig.size()).c_str() );
-
-    // add username and signature
-    txNew.userName = CScript() << strSpamUser;
-    txNew.userName += CScript() << vchSig;
-    txNew.pubKey.clear(); // pubKey will be updated to include extranonce
-    txNew.nNonce = 0; // no update needed for spamMessage's nonce.
-
-    std::vector< std::vector<unsigned char> > vData;
-    txNew.userName.ExtractPushData(vData);
-
-    printf("Verify: %d\n", pubkey.Verify(hashMsg,vData[1]));
-
-    exit(1);
-}
-
 extern void GenesisMiner();
 extern void noui_connect();
 int main(int argc, char* argv[])
@@ -190,7 +132,6 @@ int main(int argc, char* argv[])
     fHaveGUI = false;
 
     //GenesisMiner();
-    //TestCreateSpamMsgTx();
 
     // Connect bitcoind signal handlers
     noui_connect();

src/main.cpp

@@ -425,10 +425,45 @@ bool CheckTransaction(const CTransaction& tx, CValidationState &state)
 {
     // Basic checks that don't depend on any context
     if (tx.IsSpamMessage()) {
-      if (tx.message.size() > MAX_SPAM_MSG_SIZE)
-          return state.DoS(100, error("CheckTransaction() : spam message too big"));
-      // [MF] TODO: check message signature
-      // [MF] Problem: registration of this user may be in the block itself, better check later.
+        string spamMsg = tx.message.ExtractPushDataString(0);
+        if (!spamMsg.size())
+            return state.DoS(100, error("CheckTransaction() : invalid or empty spam message"));
+        if (spamMsg.size() > MAX_SPAM_MSG_SIZE)
+            return state.DoS(100, error("CheckTransaction() : spam message too big"));
+
+        string spamUser = tx.userName.ExtractPushDataString(0);
+        if( spamUser != "nobody" ) {
+            string strSign = tx.userName.ExtractPushDataString(1);
+            if (!strSign.size())
+                return state.DoS(100, error("CheckTransaction() : spam signature missing"));
+            vector<unsigned char> vchSig((const unsigned char*)strSign.data(),
+                                         (const unsigned char*)strSign.data() + strSign.size());
+
+            CPubKey pubkey;
+            CTransaction txPubKey;
+            uint256 hashBlock;
+            uint256 userhash = SerializeHash(spamUser);
+            if( !GetTransaction(userhash, txPubKey, hashBlock) )
+                return state.DoS(100, error("CheckTransaction() : spam signed by unknown user"));
+
+            std::vector< std::vector<unsigned char> > vData;
+            if( !txPubKey.pubKey.ExtractPushData(vData) || vData.size() < 1 )
+                return state.DoS(100, error("CheckTransaction() : spam signed with broken pubkey"));
+
+            pubkey = CPubKey(vData[0]);
+
+            // compute message hash for signature checking
+            CHashWriter ss(SER_GETHASH, PROTOCOL_VERSION);
+            ss << strMessageMagic;
+            ss << tx.message;
+
+            CPubKey pubkeyRec;
+            if (!pubkeyRec.RecoverCompact(ss.GetHash(), vchSig))
+                return state.DoS(100, error("CheckTransaction() : RecoverCompact failed for spammsg"));
+
+            if (pubkeyRec.GetID() != pubkey.GetID())
+                return state.DoS(100, error("CheckTransaction() : spam signature verification failed"));
+        }
     } else {
       if (tx.userName.empty())
           return state.DoS(10, error("CheckTransaction() : username empty"));
@@ -1713,11 +1748,10 @@ bool ProcessBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, CDiskBl
     if( pblock->vtx[0].IsSpamMessage() ) {
         string msg = pblock->vtx[0].message.ExtractPushDataString(0);
         string user = pblock->vtx[0].userName.ExtractPushDataString(0);
-        // [MF] FIXME: validate user properly
-        if( msg.length() <= 140 ) {
-            printf("ProcessBlock: msg='%s' user='%s'\n", msg.c_str(), user.c_str());
-            receivedSpamMessage(msg, user);
-        }
+
+        // SpamMessage was already validated in CheckBlock => CheckTransation
+        printf("ProcessBlock: msg='%s' user='%s'\n", msg.c_str(), user.c_str());
+        receivedSpamMessage(msg, user);
     }
     return true;
 }
@@ -3492,7 +3526,7 @@ static bool CreateSpamMsgTx(CTransaction &txNew, std::vector<unsigned char> &sal
     std::string strUsername = strSpamUser;
 
     CKeyID keyID;
-    if( !pwalletMain->GetKeyIdFromUsername(strSpamUser, keyID) ) {
+    if( strSpamUser != "nobody" && !pwalletMain->GetKeyIdFromUsername(strSpamUser, keyID) ) {
       if( pwalletMain->vchDefaultKey.IsValid() ) {
         keyID = pwalletMain->vchDefaultKey.GetID();
         strUsername = pwalletMain->mapKeyMetadata[keyID].username;
@@ -3534,6 +3568,10 @@ static bool CreateSpamMsgTx(CTransaction &txNew, std::vector<unsigned char> &sal
     txNew.pubKey.clear(); // pubKey will be updated to include extranonce
     txNew.nNonce = 0; // no update needed for spamMessage's nonce.
 
+    CValidationState state;
+    bool ret = CheckTransaction(txNew, state);
+    printf("CheckTransaction returned %d\n", ret );
+
     return true;
 }