From 960d144455e1012010535dfaae03c97d5cfeefe4 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sat, 24 Sep 2016 19:28:59 -0700
Subject: [PATCH] ec: start migrating towards secp256k1.

---
 lib/crypto/ec.js | 97 +++++++++++++++++++++++++++---------------------
 1 file changed, 55 insertions(+), 42 deletions(-)

diff --git a/lib/crypto/ec.js b/lib/crypto/ec.js
index d159151e..723387d8 100644
--- a/lib/crypto/ec.js
+++ b/lib/crypto/ec.js
@@ -21,6 +21,19 @@ try {
   ;
 }
 
+/*
+ * Constants
+ */
+
+var ZERO_S = new Buffer(
+  '0000000000000000000000000000000000000000000000000000000000000000',
+  'hex'
+);
+
+var HALF_ORDER = new Buffer(
+  '7fffffffffffffffffffffffffffffff5d576e7357a4501ddfe92f46681b20a0',
+  'hex');
+
 /**
  * @exports ec
  */
@@ -173,8 +186,7 @@ ec.ecdh = function ecdh(pub, priv) {
 
   if (secp256k1) {
     point = secp256k1.ecdhUnsafe(pub, priv, true);
-    point = ec.curve.decodePoint(point);
-    return point.getX().toArrayLike(Buffer, 'be', 32);
+    return point.slice(1, 33);
   }
 
   priv = ec.elliptic.keyPair({ priv: priv });
@@ -204,11 +216,13 @@ ec.recover = function recover(msg, sig, j, compressed) {
     } catch (e) {
       return;
     }
+
     try {
       key = secp256k1.recover(msg, sig, j, compressed);
     } catch (e) {
       return;
     }
+
     return key;
   }
 
@@ -248,22 +262,16 @@ ec.verify = function verify(msg, sig, key, historical, high) {
   if (key.length === 0)
     return false;
 
-  // Attempt to normalize the signature
-  // length before passing to elliptic.
-  // Note: We only do this for historical data!
-  // https://github.com/indutny/elliptic/issues/78
-  if (historical)
-    sig = ec.normalizeLength(sig);
-
   if (secp256k1) {
-    // secp256k1 fails on high s values. This is
-    // bad for verifying historical data.
-    if (high)
-      sig = ec.toLowS(sig);
-
     try {
-      // Import from DER.
-      sig = secp256k1.signatureImport(sig);
+      if (historical)
+        sig = secp256k1.signatureImportLax(sig);
+      else
+        sig = secp256k1.signatureImport(sig);
+
+      if (high)
+        sig = secp256k1.signatureNormalize(sig);
+
       result = secp256k1.verify(msg, sig, key);
     } catch (e) {
       result = false;
@@ -272,6 +280,13 @@ ec.verify = function verify(msg, sig, key, historical, high) {
     return result;
   }
 
+  // Attempt to normalize the signature
+  // length before passing to elliptic.
+  // Note: We only do this for historical data!
+  // https://github.com/indutny/elliptic/issues/78
+  if (historical)
+    sig = ec.normalizeLength(sig);
+
   // Make elliptic mimic secp256k1's
   // failure with high S values.
   if (!high && !ec.isLowS(sig))
@@ -446,14 +461,36 @@ ec.normalizeLength = function normalizeLength(sig) {
  */
 
 ec.isLowS = function isLowS(sig) {
-  if (Buffer.isBuffer(sig)) {
+  var rs, s;
+
+  if (secp256k1) {
     try {
-      sig = new ec.signature(sig);
+      rs = secp256k1.signatureImport(sig);
+      s = rs.slice(32, 64);
     } catch (e) {
       return false;
     }
+
+    if (utils.equal(s, ZERO_S))
+      return false;
+
+    // If S is greater than half the order,
+    // it's too high.
+    if (utils.cmp(s, HALF_ORDER) > 0)
+      return false;
+
+    return true;
   }
 
+  try {
+    sig = new ec.signature(sig);
+  } catch (e) {
+    return false;
+  }
+
+  if (sig.s.cmpn(0) === 0)
+    return false;
+
   // If S is greater than half the order,
   // it's too high.
   if (sig.s.cmp(ec.elliptic.nh) > 0)
@@ -462,30 +499,6 @@ ec.isLowS = function isLowS(sig) {
   return true;
 };
 
-/**
- * Lower the S value of a signature (used
- * for verifying historical data).
- * @param {Buffer} sig - DER formatted.
- * @returns {Buffer}
- */
-
-ec.toLowS = function toLowS(sig) {
-  if (Buffer.isBuffer(sig)) {
-    try {
-      sig = new ec.signature(sig);
-    } catch (e) {
-      return sig;
-    }
-  }
-
-  // If S is greater than half the order,
-  // it's too high.
-  if (sig.s.cmp(ec.elliptic.nh) > 0)
-    sig.s = ec.curve.n.sub(sig.s);
-
-  return new Buffer(sig.toDER());
-};
-
 /*
  * Helpers
  */