From dfe74fa0d23b2a0c4ba3753fabfbd27405b257b3 Mon Sep 17 00:00:00 2001
From: Daniel Cousens <github@dcousens.com>
Date: Fri, 12 Dec 2014 15:19:03 +1100
Subject: [PATCH] TxBuilder: sign now signs inputs in known publicKey order

---
 src/transaction_builder.js  | 40 +++++++++++++++++++++++++++----------
 test/transaction_builder.js | 21 +++++++++++++++++++
 2 files changed, 51 insertions(+), 10 deletions(-)

diff --git a/src/transaction_builder.js b/src/transaction_builder.js
index ede0283..d05ee5b 100644
--- a/src/transaction_builder.js
+++ b/src/transaction_builder.js
@@ -33,10 +33,9 @@ function extractSignature(txIn) {
   switch (scriptType) {
     case 'pubkeyhash':
       parsed = ECSignature.parseScriptSignature(scriptSig.chunks[0])
-      var pubKey = ECPubKey.fromBuffer(scriptSig.chunks[1])
-
       hashType = parsed.hashType
-      pubKeys = [pubKey]
+
+      pubKeys = [ECPubKey.fromBuffer(scriptSig.chunks[1])]
       signatures = [parsed.signature]
 
       break
@@ -50,6 +49,10 @@ function extractSignature(txIn) {
       pubKeys = []
       signatures = parsed.map(function(p) { return p.signature })
 
+      if (redeemScript) {
+        pubKeys = redeemScript.chunks.slice(1, -2).map(ECPubKey.fromBuffer)
+      }
+
       break
 
     case 'pubkey':
@@ -59,6 +62,10 @@ function extractSignature(txIn) {
       pubKeys = []
       signatures = [parsed.signature]
 
+      if (redeemScript) {
+        pubKeys = [ECPubKey.fromBuffer(redeemScript.chunks[0])]
+      }
+
       break
 
     default:
@@ -249,15 +256,26 @@ TransactionBuilder.prototype.sign = function(index, privKey, redeemScript, hashT
 
   var input = this.signatures[index]
   if (!input) {
+    var pubKeys = []
+
+    if (redeemScript && scriptType === 'multisig') {
+      pubKeys = redeemScript.chunks.slice(1, -2).map(ECPubKey.fromBuffer)
+
+    } else {
+      pubKeys.push(privKey.pub)
+    }
+
     input = {
       hashType: hashType,
-      pubKeys: [],
+      pubKeys: pubKeys,
       redeemScript: redeemScript,
       scriptType: scriptType,
       signatures: []
     }
 
     this.signatures[index] = input
+    this.prevOutScripts[index] = prevOutScript
+    this.prevOutTypes[index] = prevOutType
 
   } else {
     assert.equal(scriptType, 'multisig', scriptType + ' doesn\'t support multiple signatures')
@@ -265,13 +283,15 @@ TransactionBuilder.prototype.sign = function(index, privKey, redeemScript, hashT
     assert.deepEqual(input.redeemScript, redeemScript, 'Inconsistent redeemScript')
   }
 
-  this.prevOutScripts[index] = prevOutScript
-  this.prevOutTypes[index] = prevOutType
+  // enforce signing in order of public keys
+  assert(input.pubKeys.some(function(pubKey, i) {
+    if (!privKey.pub.Q.equals(pubKey.Q)) return false // FIXME: could be better?
+
+    assert(!input.signatures[i], 'Signature already exists')
+    input.signatures[i] = privKey.sign(hash)
 
-  // TODO: order signatures for multisig, enforce m < n
-  var signature = privKey.sign(hash)
-  input.pubKeys.push(privKey.pub)
-  input.signatures.push(signature)
+    return true
+  }), 'privateKey cannot sign for this input')
 }
 
 module.exports = TransactionBuilder
diff --git a/test/transaction_builder.js b/test/transaction_builder.js
index cde634b..a53cdaf 100644
--- a/test/transaction_builder.js
+++ b/test/transaction_builder.js
@@ -184,6 +184,27 @@ describe('TransactionBuilder', function() {
         }, /RedeemScript not supported \(nonstandard\)/)
       })
     })
+
+    it('throws if signature already exists', function() {
+      var redeemScript = scripts.multisigOutput(1, [privKey.pub])
+
+      txb.addInput(prevTxHash, 0)
+      txb.sign(0, privKey, redeemScript)
+
+      assert.throws(function() {
+        txb.sign(0, privKey, redeemScript)
+      }, /Signature already exists/)
+    })
+
+    it('throws if private key is unable to sign for that input', function() {
+      var redeemScript = scripts.multisigOutput(1, [privKey.pub])
+
+      txb.addInput(prevTxHash, 0)
+
+      assert.throws(function() {
+        txb.sign(0, ECKey.makeRandom(), redeemScript)
+      }, /privateKey cannot sign for this input/)
+    })
   })
 
   describe('build', function() {