/**
* Creates the initial multisig contract and incomplete refund transaction which can be requested
* at the appropriate time using {@link PaymentChannelClientState#getIncompleteRefundTransaction}
* and {@link PaymentChannelClientState#getMultisigContract()}. The way the contract is crafted
* can be adjusted by overriding {@link
* PaymentChannelClientState#editContractSendRequest(com.google.bitcoin.core.Wallet.SendRequest)}.
* By default unconfirmed coins are allowed to be used, as for micropayments the risk should be
* relatively low.
*
* @throws ValueOutOfRangeException if the value being used is too small to be accepted by the
* network
* @throws InsufficientMoneyException if the wallet doesn't contain enough balance to initiate
*/
public synchronized void initiate() throws ValueOutOfRangeException, InsufficientMoneyException {
final NetworkParameters params = wallet.getParams();
Transaction template = new Transaction(params);
// We always place the client key before the server key because, if either side wants some
// privacy, they can
// use a fresh key for the the multisig contract and nowhere else
List<ECKey> keys = Lists.newArrayList(myKey, serverMultisigKey);
// There is also probably a change output, but we don't bother shuffling them as it's obvious
// from the
// format which one is the change. If we start obfuscating the change output better in future
// this may
// be worth revisiting.
TransactionOutput multisigOutput =
template.addOutput(totalValue, ScriptBuilder.createMultiSigOutputScript(2, keys));
if (multisigOutput.getMinNonDustValue().compareTo(totalValue) > 0)
throw new ValueOutOfRangeException("totalValue too small to use");
Wallet.SendRequest req = Wallet.SendRequest.forTx(template);
req.coinSelector = AllowUnconfirmedCoinSelector.get();
editContractSendRequest(req);
req.shuffleOutputs = false; // TODO: Fix things so shuffling is usable.
wallet.completeTx(req);
Coin multisigFee = req.tx.getFee();
multisigContract = req.tx;
// Build a refund transaction that protects us in the case of a bad server that's just trying to
// cause havoc
// by locking up peoples money (perhaps as a precursor to a ransom attempt). We time lock it so
// the server
// has an assurance that we cannot take back our money by claiming a refund before the channel
// closes - this
// relies on the fact that since Bitcoin 0.8 time locked transactions are non-final. This will
// need to change
// in future as it breaks the intended design of timelocking/tx replacement, but for now it
// simplifies this
// specific protocol somewhat.
refundTx = new Transaction(params);
refundTx
.addInput(multisigOutput)
.setSequenceNumber(0); // Allow replacement when it's eventually reactivated.
refundTx.setLockTime(expiryTime);
if (totalValue.compareTo(Coin.CENT) < 0) {
// Must pay min fee.
final Coin valueAfterFee = totalValue.subtract(Transaction.REFERENCE_DEFAULT_MIN_TX_FEE);
if (Transaction.MIN_NONDUST_OUTPUT.compareTo(valueAfterFee) > 0)
throw new ValueOutOfRangeException("totalValue too small to use");
refundTx.addOutput(valueAfterFee, myKey.toAddress(params));
refundFees = multisigFee.add(Transaction.REFERENCE_DEFAULT_MIN_TX_FEE);
} else {
refundTx.addOutput(totalValue, myKey.toAddress(params));
refundFees = multisigFee;
}
refundTx.getConfidence().setSource(TransactionConfidence.Source.SELF);
log.info(
"initiated channel with multi-sig contract {}, refund {}",
multisigContract.getHashAsString(),
refundTx.getHashAsString());
state = State.INITIATED;
// Client should now call getIncompleteRefundTransaction() and send it to the server.
}
private synchronized Transaction makeUnsignedChannelContract(Coin valueToMe)
throws ValueOutOfRangeException {
Transaction tx = new Transaction(wallet.getParams());
tx.addInput(multisigContract.getOutput(0));
// Our output always comes first.
// TODO: We should drop myKey in favor of output key + multisig key separation
// (as its always obvious who the client is based on T2 output order)
tx.addOutput(valueToMe, myKey.toAddress(wallet.getParams()));
return tx;
}
/** Constructs a key from its components. This is not normally something you should use. */
public DeterministicKey(
ImmutableList<ChildNumber> childNumberPath,
byte[] chainCode,
BigInteger priv,
@Nullable DeterministicKey parent) {
super(priv, compressPoint(ECKey.publicPointFromPrivate(priv)));
checkArgument(chainCode.length == 32);
this.parent = parent;
this.childNumberPath = checkNotNull(childNumberPath);
this.chainCode = Arrays.copyOf(chainCode, chainCode.length);
this.depth = this.childNumberPath.size();
this.parentFingerprint = (parent != null) ? parent.getFingerprint() : 0;
}
/**
* Constructs a key from its components, including its private key data and possibly-redundant
* information about its parent key. Invoked when deserializing, but otherwise not something that
* you normally should use.
*/
private DeterministicKey(
ImmutableList<ChildNumber> childNumberPath,
byte[] chainCode,
BigInteger priv,
@Nullable DeterministicKey parent,
int depth,
int parentFingerprint) {
super(priv, compressPoint(ECKey.publicPointFromPrivate(priv)));
checkArgument(chainCode.length == 32);
this.parent = parent;
this.childNumberPath = checkNotNull(childNumberPath);
this.chainCode = Arrays.copyOf(chainCode, chainCode.length);
this.depth = depth;
this.parentFingerprint = ascertainParentFingerprint(parent, parentFingerprint);
}
/**
* Called when the client provides the refund transaction. The refund transaction must have one
* input from the multisig contract (that we don't have yet) and one output that the client
* creates to themselves. This object will later be modified when we start getting paid.
*
* @param refundTx The refund transaction, this object will be mutated when payment is
* incremented.
* @param clientMultiSigPubKey The client's pubkey which is required for the multisig output
* @return Our signature that makes the refund transaction valid
* @throws VerificationException If the transaction isnt valid or did not meet the requirements of
* a refund transaction.
*/
public synchronized byte[] provideRefundTransaction(
Transaction refundTx, byte[] clientMultiSigPubKey) throws VerificationException {
checkNotNull(refundTx);
checkNotNull(clientMultiSigPubKey);
checkState(state == State.WAITING_FOR_REFUND_TRANSACTION);
log.info("Provided with refund transaction: {}", refundTx);
// Do a few very basic syntax sanity checks.
refundTx.verify();
// Verify that the refund transaction has a single input (that we can fill to sign the multisig
// output).
if (refundTx.getInputs().size() != 1)
throw new VerificationException("Refund transaction does not have exactly one input");
// Verify that the refund transaction has a time lock on it and a sequence number of zero.
if (refundTx.getInput(0).getSequenceNumber() != 0)
throw new VerificationException("Refund transaction's input's sequence number is non-0");
if (refundTx.getLockTime() < minExpireTime)
throw new VerificationException("Refund transaction has a lock time too soon");
// Verify the transaction has one output (we don't care about its contents, its up to the
// client)
// Note that because we sign with SIGHASH_NONE|SIGHASH_ANYOENCANPAY the client can later add
// more outputs and
// inputs, but we will need only one output later to create the paying transactions
if (refundTx.getOutputs().size() != 1)
throw new VerificationException("Refund transaction does not have exactly one output");
refundTransactionUnlockTimeSecs = refundTx.getLockTime();
// Sign the refund tx with the scriptPubKey and return the signature. We don't have the spending
// transaction
// so do the steps individually.
clientKey = ECKey.fromPublicOnly(clientMultiSigPubKey);
Script multisigPubKey =
ScriptBuilder.createMultiSigOutputScript(2, ImmutableList.of(clientKey, serverKey));
// We are really only signing the fact that the transaction has a proper lock time and don't
// care about anything
// else, so we sign SIGHASH_NONE and SIGHASH_ANYONECANPAY.
TransactionSignature sig =
refundTx.calculateSignature(0, serverKey, multisigPubKey, Transaction.SigHash.NONE, true);
log.info("Signed refund transaction.");
this.clientOutput = refundTx.getOutput(0);
state = State.WAITING_FOR_MULTISIG_CONTRACT;
return sig.encodeToBitcoin();
}
PaymentChannelServerState(
StoredServerChannel storedServerChannel, Wallet wallet, TransactionBroadcaster broadcaster)
throws VerificationException {
synchronized (storedServerChannel) {
this.wallet = checkNotNull(wallet);
this.broadcaster = checkNotNull(broadcaster);
this.multisigContract = checkNotNull(storedServerChannel.contract);
this.multisigScript = multisigContract.getOutput(0).getScriptPubKey();
this.clientKey = ECKey.fromPublicOnly(multisigScript.getChunks().get(1).data);
this.clientOutput = checkNotNull(storedServerChannel.clientOutput);
this.refundTransactionUnlockTimeSecs = storedServerChannel.refundTransactionUnlockTimeSecs;
this.serverKey = checkNotNull(storedServerChannel.myKey);
this.totalValue = multisigContract.getOutput(0).getValue();
this.bestValueToMe = checkNotNull(storedServerChannel.bestValueToMe);
this.bestValueSignature = storedServerChannel.bestValueSignature;
checkArgument(bestValueToMe.equals(Coin.ZERO) || bestValueSignature != null);
this.storedServerChannel = storedServerChannel;
storedServerChannel.state = this;
this.state = State.READY;
}
}
/**
* Called when the client provides us with a new signature and wishes to increment total payment
* by size. Verifies the provided signature and only updates values if everything checks out. If
* the new refundSize is not the lowest we have seen, it is simply ignored.
*
* @param refundSize How many satoshis of the original contract are refunded to the client (the
* rest are ours)
* @param signatureBytes The new signature spending the multi-sig contract to a new payment
* transaction
* @throws VerificationException If the signature does not verify or size is out of range (incl
* being rejected by the network as dust).
* @return true if there is more value left on the channel, false if it is now fully used up.
*/
public synchronized boolean incrementPayment(Coin refundSize, byte[] signatureBytes)
throws VerificationException, ValueOutOfRangeException, InsufficientMoneyException {
checkState(state == State.READY);
checkNotNull(refundSize);
checkNotNull(signatureBytes);
TransactionSignature signature = TransactionSignature.decodeFromBitcoin(signatureBytes, true);
// We allow snapping to zero for the payment amount because it's treated specially later, but
// not less than
// the dust level because that would prevent the transaction from being relayed/mined.
final boolean fullyUsedUp = refundSize.equals(Coin.ZERO);
if (refundSize.compareTo(clientOutput.getMinNonDustValue()) < 0 && !fullyUsedUp)
throw new ValueOutOfRangeException(
"Attempt to refund negative value or value too small to be accepted by the network");
Coin newValueToMe = totalValue.subtract(refundSize);
if (newValueToMe.signum() < 0)
throw new ValueOutOfRangeException("Attempt to refund more than the contract allows.");
if (newValueToMe.compareTo(bestValueToMe) < 0)
throw new ValueOutOfRangeException("Attempt to roll back payment on the channel.");
// Get the wallet's copy of the multisigContract (ie with confidence information), if this is
// null, the wallet
// was not connected to the peergroup when the contract was broadcast (which may cause issues
// down the road, and
// disables our double-spend check next)
Transaction walletContract = wallet.getTransaction(multisigContract.getHash());
checkNotNull(
walletContract,
"Wallet did not contain multisig contract {} after state was marked READY",
multisigContract.getHash());
// Note that we check for DEAD state here, but this test is essentially useless in production
// because we will
// miss most double-spends due to bloom filtering right now anyway. This will eventually fixed
// by network-wide
// double-spend notifications, so we just wait instead of attempting to add all dependant
// outpoints to our bloom
// filters (and probably missing lots of edge-cases).
if (walletContract.getConfidence().getConfidenceType()
== TransactionConfidence.ConfidenceType.DEAD) {
close();
throw new VerificationException("Multisig contract was double-spent");
}
Transaction.SigHash mode;
// If the client doesn't want anything back, they shouldn't sign any outputs at all.
if (fullyUsedUp) mode = Transaction.SigHash.NONE;
else mode = Transaction.SigHash.SINGLE;
if (signature.sigHashMode() != mode || !signature.anyoneCanPay())
throw new VerificationException(
"New payment signature was not signed with the right SIGHASH flags.");
Wallet.SendRequest req = makeUnsignedChannelContract(newValueToMe);
// Now check the signature is correct.
// Note that the client must sign with SIGHASH_{SINGLE/NONE} | SIGHASH_ANYONECANPAY to allow us
// to add additional
// inputs (in case we need to add significant fee, or something...) and any outputs we want to
// pay to.
Sha256Hash sighash = req.tx.hashForSignature(0, multisigScript, mode, true);
if (!clientKey.verify(sighash, signature))
throw new VerificationException("Signature does not verify on tx\n" + req.tx);
bestValueToMe = newValueToMe;
bestValueSignature = signatureBytes;
updateChannelInWallet();
return !fullyUsedUp;
}
/**
* The creation time of a deterministic key is equal to that of its parent, unless this key is the
* root of a tree. Thus, setting the creation time on a leaf is forbidden.
*/
@Override
public void setCreationTimeSeconds(long newCreationTimeSeconds) {
if (parent != null)
throw new IllegalStateException("Creation time can only be set on root keys.");
else super.setCreationTimeSeconds(newCreationTimeSeconds);
}