From 671a5aec18654a8ef9d7beedbdc46362b1e13742 Mon Sep 17 00:00:00 2001
From: Mike Hearn <hearn@google.com>
Date: Wed, 26 Dec 2012 18:14:39 +0000
Subject: [PATCH] Add a TransactionInput.verify() method that checks signatures
 and use it from the basicSpending test to ensure we generate valid
 signatures/scripts.

---
 .../java/com/google/bitcoin/core/Script.java     | 16 +++++++++++-----
 .../google/bitcoin/core/TransactionInput.java    | 13 +++++++++++++
 .../java/com/google/bitcoin/core/WalletTest.java |  4 ++--
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/core/src/main/java/com/google/bitcoin/core/Script.java b/core/src/main/java/com/google/bitcoin/core/Script.java
index 520e51ab..98043c09 100644
--- a/core/src/main/java/com/google/bitcoin/core/Script.java
+++ b/core/src/main/java/com/google/bitcoin/core/Script.java
@@ -875,7 +875,8 @@ public class Script {
         return Utils.decodeMPI(Utils.reverseBytes(chunk), false);
     }
     
-    private static void executeScript(Transaction txContainingThis, long index, Script script, LinkedList<byte[]> stack) throws ScriptException {
+    private static void executeScript(Transaction txContainingThis, long index,
+                                      Script script, LinkedList<byte[]> stack) throws ScriptException {
         int opCount = 0;
         int lastCodeSepLocation = 0;
         
@@ -1479,19 +1480,24 @@ public class Script {
 
     /**
      * Verifies that this script (interpreted as a scriptSig) correctly spends the given scriptPubKey.
+     * @param txContainingThis The transaction in which this input scriptSig resides.
+     * @param scriptSigIndex The index in txContainingThis of the scriptSig (note: NOT the index of the scriptPubKey).
+     * @param scriptPubKey The connected scriptPubKey containing the conditions needed to claim the value.
+     * @param enforceP2SH Whether "pay to script hash" rules should be enforced. If in doubt, set to true.
      * @throws VerificationException if this script does not correctly spend the scriptPubKey
      */
-    public void correctlySpends(Transaction txContainingThis, long index, Script scriptPubKey, boolean enforceP2SH) throws ScriptException {
+    public void correctlySpends(Transaction txContainingThis, long scriptSigIndex, Script scriptPubKey,
+                                boolean enforceP2SH) throws ScriptException {
         if (program.length > 10000 || scriptPubKey.program.length > 10000)
             throw new ScriptException("Script larger than 10,000 bytes");
         
         LinkedList<byte[]> stack = new LinkedList<byte[]>();
         LinkedList<byte[]> p2shStack = null;
         
-        executeScript(txContainingThis, index, this, stack);
+        executeScript(txContainingThis, scriptSigIndex, this, stack);
         if (enforceP2SH)
             p2shStack = new LinkedList<byte[]>(stack);
-        executeScript(txContainingThis, index, scriptPubKey, stack);
+        executeScript(txContainingThis, scriptSigIndex, scriptPubKey, stack);
         
         if (stack.size() == 0)
             throw new ScriptException("Stack empty at end of script execution.");
@@ -1520,7 +1526,7 @@ public class Script {
             byte[] scriptPubKeyBytes = p2shStack.pollLast();
             Script scriptPubKeyP2SH = new Script(params, scriptPubKeyBytes, 0, scriptPubKeyBytes.length);
             
-            executeScript(txContainingThis, index, scriptPubKeyP2SH, p2shStack);
+            executeScript(txContainingThis, scriptSigIndex, scriptPubKeyP2SH, p2shStack);
             
             if (p2shStack.size() == 0)
                 throw new ScriptException("P2SH stack empty at end of script execution.");
diff --git a/core/src/main/java/com/google/bitcoin/core/TransactionInput.java b/core/src/main/java/com/google/bitcoin/core/TransactionInput.java
index d4279069..b4c66039 100644
--- a/core/src/main/java/com/google/bitcoin/core/TransactionInput.java
+++ b/core/src/main/java/com/google/bitcoin/core/TransactionInput.java
@@ -340,4 +340,17 @@ public class TransactionInput extends ChildMessage implements Serializable {
     public boolean hasSequence() {
         return sequence != NO_SEQUENCE;
     }
+
+    /**
+     * For a connected transaction, runs the script against the connected pubkey and verifies they are correct.
+     * @throws ScriptException if the script did not verify.
+     */
+    public void verify() throws ScriptException {
+        Preconditions.checkNotNull(getOutpoint().fromTx, "Not connected");
+        long spendingIndex = getOutpoint().getIndex();
+        Script pubKey = getOutpoint().fromTx.getOutputs().get((int) spendingIndex).getScriptPubKey();
+        Script sig = getScriptSig();
+        int myIndex = parentTransaction.getInputs().indexOf(this);
+        sig.correctlySpends(parentTransaction, myIndex, pubKey, true);
+    }
 }
diff --git a/core/src/test/java/com/google/bitcoin/core/WalletTest.java b/core/src/test/java/com/google/bitcoin/core/WalletTest.java
index 3c4b9249..670fb5fb 100644
--- a/core/src/test/java/com/google/bitcoin/core/WalletTest.java
+++ b/core/src/test/java/com/google/bitcoin/core/WalletTest.java
@@ -89,8 +89,8 @@ public class WalletTest {
         assertEquals(destination, t2.getOutputs().get(0).getScriptPubKey().getToAddress());
         assertEquals(wallet.getChangeAddress(), t2.getOutputs().get(1).getScriptPubKey().getToAddress());
         assertEquals(toNanoCoins(0, 49), t2.getOutputs().get(1).getValue());
-
-        // We have NOT proven that the signature is correct!
+        // Check the script runs and signatures verify.
+        t2.getInputs().get(0).verify();
 
         final LinkedList<Transaction> txns = Lists.newLinkedList();
         wallet.addEventListener(new AbstractWalletEventListener() {