From 3b402d00c61fc50a290a8d3f6bfb3749b8c13e63 Mon Sep 17 00:00:00 2001
From: junderw <junderwood@bitcoinbank.co.jp>
Date: Fri, 12 Apr 2019 17:44:55 +0900
Subject: [PATCH] Add low R grinding option

---
 src/ecpair.js     | 19 +++++++++++++++++--
 ts_src/ecpair.ts  | 18 ++++++++++++++++--
 types/ecpair.d.ts |  2 +-
 3 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/src/ecpair.js b/src/ecpair.js
index 2026c63..6bb7eb9 100644
--- a/src/ecpair.js
+++ b/src/ecpair.js
@@ -35,10 +35,25 @@ class ECPair {
             throw new Error('Missing private key');
         return wif.encode(this.network.wif, this.__D, this.compressed);
     }
-    sign(hash) {
+    sign(hash, lowR = false) {
         if (!this.__D)
             throw new Error('Missing private key');
-        return ecc.sign(hash, this.__D);
+        if (lowR === false) {
+            return ecc.sign(hash, this.__D);
+        }
+        else {
+            let sig = ecc.sign(hash, this.__D);
+            const extraData = Buffer.alloc(32, 0);
+            let counter = 0;
+            // if first try is lowR, skip the loop
+            // for second try and on, add extra entropy counting up
+            while (sig[0] > 0x7f) {
+                counter++;
+                extraData.writeUIntLE(counter, 0, 6);
+                sig = ecc.signWithEntropy(hash, this.__D, extraData);
+            }
+            return sig;
+        }
     }
     verify(hash, signature) {
         return ecc.verify(hash, this.publicKey, signature);
diff --git a/ts_src/ecpair.ts b/ts_src/ecpair.ts
index 3941afa..7245d0d 100644
--- a/ts_src/ecpair.ts
+++ b/ts_src/ecpair.ts
@@ -61,9 +61,23 @@ class ECPair implements ECPairInterface {
     return wif.encode(this.network.wif, this.__D, this.compressed);
   }
 
-  sign(hash: Buffer): Buffer {
+  sign(hash: Buffer, lowR: boolean = false): Buffer {
     if (!this.__D) throw new Error('Missing private key');
-    return ecc.sign(hash, this.__D);
+    if (lowR === false) {
+      return ecc.sign(hash, this.__D);
+    } else {
+      let sig = ecc.sign(hash, this.__D);
+      const extraData = Buffer.alloc(32, 0);
+      let counter = 0;
+      // if first try is lowR, skip the loop
+      // for second try and on, add extra entropy counting up
+      while (sig[0] > 0x7f) {
+        counter++;
+        extraData.writeUIntLE(counter, 0, 6);
+        sig = ecc.signWithEntropy(hash, this.__D, extraData);
+      }
+      return sig;
+    }
   }
 
   verify(hash: Buffer, signature: Buffer): Buffer {
diff --git a/types/ecpair.d.ts b/types/ecpair.d.ts
index a5ae716..2f9bbc4 100644
--- a/types/ecpair.d.ts
+++ b/types/ecpair.d.ts
@@ -24,7 +24,7 @@ declare class ECPair implements ECPairInterface {
     readonly privateKey: Buffer | undefined;
     readonly publicKey: Buffer | undefined;
     toWIF(): string;
-    sign(hash: Buffer): Buffer;
+    sign(hash: Buffer, lowR?: boolean): Buffer;
     verify(hash: Buffer, signature: Buffer): Buffer;
 }
 declare function fromPrivateKey(buffer: Buffer, options?: ECPairOptions): ECPair;