hush3/src/cc/channels.cpp

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#include "CCChannels.h"

/*
 The idea here is to allow instant (mempool) payments that are secured by dPoW. In order to simplify things, channels CC will require creating reserves for each payee locked in the destination user's CC address. This will look like the payment is already made, but it is locked until further released. The dPoW protection comes from the cancel channel having a delayed effect until the next notarization. This way, if a payment release is made and the chain reorged, the same payment release will still be valid when it is re-broadcast into the mempool.
 
 In order to achieve this effect, the payment release needs to be in a special form where its input cannot be spent only by the sender.

 Given sender's payment to dest CC address, only the destination is able to spend, so we need to constrain that spending with a release mechanism. One idea is a 2of2 multisig, but that has the issue of needing confirmation and since a sender utxo is involved, subject to doublespend and we lose the speed. Another idea is release on secrets! since once revealed, the secret remains valid, this method is immune from double spend. Also, there is no worry about an MITM attack as the funds are only spendable by the destination pubkey and only with the secret. The secrets can be sent via any means, including OP_RETURN of normal transaction in the mempool.
 
 Now the only remaining issue for sending is how to allocate funds to the secrets. This needs to be sent as hashes of secrets when the channel is created. A bruteforce method would be one secret per COIN, but for large amount channels this is cumbersome. A more practical approach is to have a set of secrets for each order of magnitude:
 
 123.45 channel funds -> 1x secret100, 2x secret10, 3x secret1, 4x secret.1, 5x secret.01
 15 secrets achieves the 123.45 channel funding.
 
 In order to avoid networking issues, the convention can be to send tx to normal address of destination with just an OP_RETURN, for the cost of txfee. For micropayments, a separate method of secret release needs to be established, but that is beyond the scope of this CC.
 
 There is now the dPoW security that needs to be ensured. In order to close the channel, a tx needs to be confirmed that cancels the channel. As soon as this tx is seen, the destination will know that the channel will be closing soon, if the node is online. If not, the payments cant be credited anyway, so it seems no harm. Even after the channel is closed, it is possible for secrets to be releasing funds, but depending on when the notarization happens, it could invalidate the spends, so it is safest that as soon as the channel cancel tx is confirmed to invalidate any further payments released.
 
 Given a channelclose and notarization confirmation (or enough blocks), the remaining funds needs to be able to come back to the sender. this means the funds need to be in a 1of2 CC multisig to allow either party to spend. Cheating is prevented by the additional rules of spending, ie. denomination secrets, or channelclose.
 
 For efficiency we want to allow batch spend with multiple secrets to claim a single total
 
*/

// start of consensus code

int64_t IsChannelsvout(struct CCcontract_info *cp,const CTransaction& tx,int32_t v)
{
    char destaddr[64];
    if ( tx.vout[v].scriptPubKey.IsPayToCryptoCondition() != 0 )
    {
        if ( Getscriptaddress(destaddr,tx.vout[v].scriptPubKey) > 0 && strcmp(destaddr,cp->unspendableCCaddr) == 0 )
            return(tx.vout[v].nValue);
    }
    return(0);
}

bool ChannelsExactAmounts(struct CCcontract_info *cp,Eval* eval,const CTransaction &tx,int32_t minage,uint64_t txfee)
{
    static uint256 zerohash;
    CTransaction vinTx; uint256 hashBlock,activehash; int32_t i,numvins,numvouts; int64_t inputs=0,outputs=0,assetoshis;
    numvins = tx.vin.size();
    numvouts = tx.vout.size();
    for (i=0; i<numvins; i++)
    {
        //fprintf(stderr,"vini.%d\n",i);
        if ( (*cp->ismyvin)(tx.vin[i].scriptSig) != 0 )
        {
            //fprintf(stderr,"vini.%d check mempool\n",i);
            if ( eval->GetTxUnconfirmed(tx.vin[i].prevout.hash,vinTx,hashBlock) == 0 )
                return eval->Invalid("cant find vinTx");
            else
            {
                //fprintf(stderr,"vini.%d check hash and vout\n",i);
                if ( hashBlock == zerohash )
                    return eval->Invalid("cant Channels from mempool");
                if ( (assetoshis= IsChannelsvout(cp,vinTx,tx.vin[i].prevout.n)) != 0 )
                    inputs += assetoshis;
            }
        }
    }
    for (i=0; i<numvouts; i++)
    {
        //fprintf(stderr,"i.%d of numvouts.%d\n",i,numvouts);
        if ( (assetoshis= IsChannelsvout(cp,tx,i)) != 0 )
            outputs += assetoshis;
    }
    if ( inputs != outputs+txfee )
    {
        fprintf(stderr,"inputs %llu vs outputs %llu\n",(long long)inputs,(long long)outputs);
        return eval->Invalid("mismatched inputs != outputs + txfee");
    }
    else return(true);
}

bool ChannelsValidate(struct CCcontract_info *cp,Eval* eval,const CTransaction &tx)
{
    int32_t numvins,numvouts,preventCCvins,preventCCvouts,i,numblocks; bool retval; uint256 txid; uint8_t hash[32]; char str[65],destaddr[64];
    return(false);
    std::vector<std::pair<CAddressIndexKey, CAmount> > txids;
    numvins = tx.vin.size();
    numvouts = tx.vout.size();
    preventCCvins = preventCCvouts = -1;
    if ( numvouts < 1 )
        return eval->Invalid("no vouts");
    else
    {
        for (i=0; i<numvins; i++)
        {
            if ( IsCCInput(tx.vin[0].scriptSig) == 0 )
            {
                return eval->Invalid("illegal normal vini");
            }
        }
        //fprintf(stderr,"check amounts\n");
        if ( ChannelsExactAmounts(cp,eval,tx,1,10000) == false )
        {
            fprintf(stderr,"Channelsget invalid amount\n");
            return false;
        }
        else
        {
            txid = tx.GetHash();
            memcpy(hash,&txid,sizeof(hash));
            retval = PreventCC(eval,tx,preventCCvins,numvins,preventCCvouts,numvouts);
            if ( retval != 0 )
                fprintf(stderr,"Channelsget validated\n");
            else fprintf(stderr,"Channelsget invalid\n");
            return(retval);
        }
    }
}
// end of consensus code

// helper functions for rpc calls in rpcwallet.cpp

int64_t AddChannelsInputs(struct CCcontract_info *cp,CMutableTransaction &mtx,CPubKey pk,int64_t total,int32_t maxinputs)
{
    char coinaddr[64]; int64_t nValue,price,totalinputs = 0; uint256 txid,hashBlock; std::vector<uint8_t> origpubkey; CTransaction vintx; int32_t vout,n = 0;
    std::vector<std::pair<CAddressUnspentKey, CAddressUnspentValue> > unspentOutputs;
    GetCCaddress(cp,coinaddr,pk);
    SetCCunspents(unspentOutputs,coinaddr);
    for (std::vector<std::pair<CAddressUnspentKey, CAddressUnspentValue> >::const_iterator it=unspentOutputs.begin(); it!=unspentOutputs.end(); it++)
    {
        txid = it->first.txhash;
        vout = (int32_t)it->first.index;
        // no need to prevent dup
        if ( GetTransaction(txid,vintx,hashBlock,false) != 0 )
        {
            if ( (nValue= IsChannelsvout(cp,vintx,vout)) > 1000000 && myIsutxo_spentinmempool(txid,vout) == 0 )
            {
                if ( total != 0 && maxinputs != 0 )
                    mtx.vin.push_back(CTxIn(txid,vout,CScript()));
                nValue = it->second.satoshis;
                totalinputs += nValue;
                n++;
                if ( (total > 0 && totalinputs >= total) || (maxinputs > 0 && n >= maxinputs) )
                    break;
            }
        }
    }
    return(totalinputs);
}

std::string ChannelsGet(uint64_t txfee,int64_t nValue)
{
    CMutableTransaction mtx,tmpmtx; CPubKey mypk,Channelspk; int64_t inputs,CCchange=0; struct CCcontract_info *cp,C; std::string rawhex; uint32_t j; int32_t i,len; uint8_t buf[32768]; bits256 hash;
    cp = CCinit(&C,EVAL_CHANNELS);
    if ( txfee == 0 )
        txfee = 10000;
    Channelspk = GetUnspendable(cp,0);
    mypk = pubkey2pk(Mypubkey());
    if ( (inputs= AddChannelsInputs(cp,mtx,Channelspk,nValue+txfee,60)) > 0 )
    {
        if ( inputs > nValue )
            CCchange = (inputs - nValue - txfee);
        if ( CCchange != 0 )
            mtx.vout.push_back(MakeCC1vout(EVAL_CHANNELS,CCchange,Channelspk));
        mtx.vout.push_back(CTxOut(nValue,CScript() << ParseHex(HexStr(mypk)) << OP_CHECKSIG));
        fprintf(stderr,"start at %u\n",(uint32_t)time(NULL));
        j = rand() & 0xfffffff;
        for (i=0; i<1000000; i++,j++)
        {
            tmpmtx = mtx;
            rawhex = FinalizeCCTx(-1LL,cp,tmpmtx,mypk,txfee,CScript() << OP_RETURN << E_MARSHAL(ss << (uint8_t)EVAL_CHANNELS << (uint8_t)'G' << j));
            if ( (len= (int32_t)rawhex.size()) > 0 && len < 65536 )
            {
                len >>= 1;
                decode_hex(buf,len,(char *)rawhex.c_str());
                hash = bits256_doublesha256(0,buf,len);
                if ( (hash.bytes[0] & 0xff) == 0 && (hash.bytes[31] & 0xff) == 0 )
                {
                    fprintf(stderr,"found valid txid after %d iterations %u\n",i,(uint32_t)time(NULL));
                    return(rawhex);
                }
                //fprintf(stderr,"%02x%02x ",hash.bytes[0],hash.bytes[31]);
            }
        }
        fprintf(stderr,"couldnt generate valid txid %u\n",(uint32_t)time(NULL));
        return("");
    } else fprintf(stderr,"cant find Channels inputs\n");
    return("");
}

std::string ChannelsFund(uint64_t txfee,int64_t funds)
{
    CMutableTransaction mtx; CPubKey mypk,Channelspk; CScript opret; struct CCcontract_info *cp,C;
    cp = CCinit(&C,EVAL_CHANNELS);
    if ( txfee == 0 )
        txfee = 10000;
    mypk = pubkey2pk(Mypubkey());
    Channelspk = GetUnspendable(cp,0);
    if ( AddNormalinputs(mtx,mypk,funds+txfee,64) > 0 )
    {
        mtx.vout.push_back(MakeCC1vout(EVAL_CHANNELS,funds,Channelspk));
        return(FinalizeCCTx(0,cp,mtx,mypk,txfee,opret));
    }
    return("");
}

UniValue ChannelsInfo()
{
    UniValue result(UniValue::VOBJ); char numstr[64];
    CMutableTransaction mtx; CPubKey Channelspk; struct CCcontract_info *cp,C; int64_t funding;
    result.push_back(Pair("result","success"));
    result.push_back(Pair("name","Channels"));
    cp = CCinit(&C,EVAL_CHANNELS);
    Channelspk = GetUnspendable(cp,0);
    funding = AddChannelsInputs(cp,mtx,Channelspk,0,0);
    sprintf(numstr,"%.8f",(double)funding/COIN);
    result.push_back(Pair("funding",numstr));
    return(result);
}