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/*
* Copyright 2013 Google Inc.
* Copyright 2014 Andreas Schildbach
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.bitcoinj.wallet;
import org.bitcoinj.core.Coin;
import org.bitcoinj.core.ECKey;
import org.bitcoinj.core.ECKey.ECDSASignature;
import org.bitcoinj.core.NetworkParameters;
import org.bitcoinj.core.SignatureDecodeException;
import org.bitcoinj.core.Transaction;
import org.bitcoinj.core.TransactionConfidence;
import org.bitcoinj.core.TransactionInput;
import org.bitcoinj.core.TransactionOutput;
import org.bitcoinj.crypto.TransactionSignature;
import org.bitcoinj.script.ScriptChunk;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.annotation.Nullable;
import java.util.List;
import static com.google.common.base.Preconditions.checkState;
/**
* The default risk analysis. Currently, it only is concerned with whether a tx/dependency is non-final or not, and
* whether a tx/dependency violates the dust rules. Outside of specialised protocols you should not encounter non-final
* transactions.
*/
public class DefaultRiskAnalysis implements RiskAnalysis {
private static final Logger log = LoggerFactory.getLogger(DefaultRiskAnalysis.class);
/**
* Any standard output smaller than this value (in satoshis) will be considered risky, as it's most likely be
* rejected by the network. This is usually the same as {@link Transaction#MIN_NONDUST_OUTPUT} but can be
* different when the fee is about to change in Bitcoin Core.
*/
public static final Coin MIN_ANALYSIS_NONDUST_OUTPUT = Transaction.MIN_NONDUST_OUTPUT;
protected final Transaction tx;
protected final List dependencies;
@Nullable protected final Wallet wallet;
private Transaction nonStandard;
protected Transaction nonFinal;
protected boolean analyzed;
private DefaultRiskAnalysis(Wallet wallet, Transaction tx, List dependencies) {
this.tx = tx;
this.dependencies = dependencies;
this.wallet = wallet;
}
@Override
public Result analyze() {
checkState(!analyzed);
analyzed = true;
Result result = analyzeIsFinal();
if (result != null && result != Result.OK)
return result;
return analyzeIsStandard();
}
@Nullable
private Result analyzeIsFinal() {
// Transactions we create ourselves are, by definition, not at risk of double spending against us.
if (tx.getConfidence().getSource() == TransactionConfidence.Source.SELF)
return Result.OK;
// We consider transactions that opt into replace-by-fee at risk of double spending.
if (tx.isOptInFullRBF()) {
nonFinal = tx;
return Result.NON_FINAL;
}
// Relative time-locked transactions are risky too. We can't check the locks because usually we don't know the
// spent outputs (to know when they were created).
if (tx.hasRelativeLockTime()) {
nonFinal = tx;
return Result.NON_FINAL;
}
if (wallet == null)
return null;
final int height = wallet.getLastBlockSeenHeight();
final long time = wallet.getLastBlockSeenTimeSecs();
// If the transaction has a lock time specified in blocks, we consider that if the tx would become final in the
// next block it is not risky (as it would confirm normally).
final int adjustedHeight = height + 1;
if (!tx.isFinal(adjustedHeight, time)) {
nonFinal = tx;
return Result.NON_FINAL;
}
for (Transaction dep : dependencies) {
if (!dep.isFinal(adjustedHeight, time)) {
nonFinal = dep;
return Result.NON_FINAL;
}
}
return Result.OK;
}
/**
* The reason a transaction is considered non-standard, returned by
* {@link #isStandard(Transaction)}.
*/
public enum RuleViolation {
NONE,
VERSION,
DUST,
SHORTEST_POSSIBLE_PUSHDATA,
NONEMPTY_STACK, // Not yet implemented (for post 0.12)
SIGNATURE_CANONICAL_ENCODING
}
/**
* Checks if a transaction is considered "standard" by Bitcoin Core's IsStandardTx and AreInputsStandard
* functions.
*
* Note that this method currently only implements a minimum of checks. More to be added later.
*/
public static RuleViolation isStandard(Transaction tx) {
// TODO: Finish this function off.
if (tx.getVersion() > 2 || tx.getVersion() < 1) {
log.warn("TX considered non-standard due to unknown version number {}", tx.getVersion());
return RuleViolation.VERSION;
}
final List outputs = tx.getOutputs();
for (int i = 0; i < outputs.size(); i++) {
TransactionOutput output = outputs.get(i);
RuleViolation violation = isOutputStandard(output);
if (violation != RuleViolation.NONE) {
log.warn("TX considered non-standard due to output {} violating rule {}", i, violation);
return violation;
}
}
final List inputs = tx.getInputs();
for (int i = 0; i < inputs.size(); i++) {
TransactionInput input = inputs.get(i);
RuleViolation violation = isInputStandard(input);
if (violation != RuleViolation.NONE) {
log.warn("TX considered non-standard due to input {} violating rule {}", i, violation);
return violation;
}
}
return RuleViolation.NONE;
}
/**
* Checks the output to see if the script violates a standardness rule. Not complete.
*/
public static RuleViolation isOutputStandard(TransactionOutput output) {
if (output.getValue().compareTo(MIN_ANALYSIS_NONDUST_OUTPUT) < 0)
return RuleViolation.DUST;
for (ScriptChunk chunk : output.getScriptPubKey().getChunks()) {
if (chunk.isPushData() && !chunk.isShortestPossiblePushData())
return RuleViolation.SHORTEST_POSSIBLE_PUSHDATA;
}
return RuleViolation.NONE;
}
/** Checks if the given input passes some of the AreInputsStandard checks. Not complete. */
public static RuleViolation isInputStandard(TransactionInput input) {
for (ScriptChunk chunk : input.getScriptSig().getChunks()) {
if (chunk.data != null && !chunk.isShortestPossiblePushData())
return RuleViolation.SHORTEST_POSSIBLE_PUSHDATA;
if (chunk.isPushData()) {
ECDSASignature signature;
try {
signature = ECKey.ECDSASignature.decodeFromDER(chunk.data);
} catch (SignatureDecodeException x) {
// Doesn't look like a signature.
signature = null;
}
if (signature != null) {
if (!TransactionSignature.isEncodingCanonical(chunk.data))
return RuleViolation.SIGNATURE_CANONICAL_ENCODING;
if (!signature.isCanonical())
return RuleViolation.SIGNATURE_CANONICAL_ENCODING;
}
}
}
return RuleViolation.NONE;
}
private Result analyzeIsStandard() {
// The IsStandard rules don't apply on testnet, because they're just a safety mechanism and we don't want to
// crush innovation with valueless test coins.
if (wallet != null && !wallet.getNetworkParameters().getId().equals(NetworkParameters.ID_MAINNET))
return Result.OK;
RuleViolation ruleViolation = isStandard(tx);
if (ruleViolation != RuleViolation.NONE) {
nonStandard = tx;
return Result.NON_STANDARD;
}
for (Transaction dep : dependencies) {
ruleViolation = isStandard(dep);
if (ruleViolation != RuleViolation.NONE) {
nonStandard = dep;
return Result.NON_STANDARD;
}
}
return Result.OK;
}
/** Returns the transaction that was found to be non-standard, or null. */
@Nullable
public Transaction getNonStandard() {
return nonStandard;
}
/** Returns the transaction that was found to be non-final, or null. */
@Nullable
public Transaction getNonFinal() {
return nonFinal;
}
@Override
public String toString() {
if (!analyzed)
return "Pending risk analysis for " + tx.getTxId();
else if (nonFinal != null)
return "Risky due to non-finality of " + nonFinal.getTxId();
else if (nonStandard != null)
return "Risky due to non-standard tx " + nonStandard.getTxId();
else
return "Non-risky";
}
public static class Analyzer implements RiskAnalysis.Analyzer {
@Override
public DefaultRiskAnalysis create(Wallet wallet, Transaction tx, List dependencies) {
return new DefaultRiskAnalysis(wallet, tx, dependencies);
}
}
public static Analyzer FACTORY = new Analyzer();
}
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