From fea199d1c8ef8198bde5d6a8af81c4c65db53312 Mon Sep 17 00:00:00 2001
From: Shun Usami <usatie@gmail.com>
Date: Thu, 12 Sep 2019 22:12:19 +0900
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=9B=20Fix=20Private=20key=20derivation?=
 =?UTF-8?q?=20bug?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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- Pads with 0 if length is less than 32 bytes
---
 .../BitcoinKit.Private.swift                  |  5 ++++-
 Tests/BitcoinKitTests/HDPrivateKeyTests.swift | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/Sources/BitcoinKitPrivate/BitcoinKit.Private.swift b/Sources/BitcoinKitPrivate/BitcoinKit.Private.swift
index c6e581fd..81dd1634 100644
--- a/Sources/BitcoinKitPrivate/BitcoinKit.Private.swift
+++ b/Sources/BitcoinKitPrivate/BitcoinKit.Private.swift
@@ -180,7 +180,7 @@ public class _HDKey {
             return nil
         }
         
-        var result: Data = Data()
+        var result: Data
         if let privateKey = self.privateKey {
             let privateKeyNum = BN_new()!
             defer {
@@ -205,6 +205,9 @@ public class _HDKey {
                 BN_bn2bin(privateKeyNum, ptr)
                 return
             }
+            if result.count < 32 {
+                result = Data(repeating: 0, count: 32 - result.count) + result // 0 padding
+            }
         } else {
             let publicKeyNum = BN_new()
             defer {
diff --git a/Tests/BitcoinKitTests/HDPrivateKeyTests.swift b/Tests/BitcoinKitTests/HDPrivateKeyTests.swift
index 7d605605..725c5334 100644
--- a/Tests/BitcoinKitTests/HDPrivateKeyTests.swift
+++ b/Tests/BitcoinKitTests/HDPrivateKeyTests.swift
@@ -174,4 +174,23 @@ class HDPrivateKeyTests: XCTestCase {
         let m011pub = try! m01prv.extendedPublicKey().derived(at: 1)
         XCTAssertEqual(m011pub.extended(), "xpub6D4BDPcEgbv6teFCGk7PMijta2aSGvRbvFX8dthHedYVVMM8QBf9xp9TF6TeuHYD9xiHGcuGNZQkKmD9jvojPj7YqnqtB3iYXv3f8s1JzwS")
     }
+    
+    // https://github.com/yenom/BitcoinKit/issues/73
+    func testDeriveProblem() {
+        let seed = Data(hex: "f27fd395d30d00f1c11b7551a93961ca41c0a78bce21e9a618e83a99cf74aec159139ef3ef078bc0038557b7cb689933d0806ce33571df78bc4397e7f9976ff2")!
+        
+        let key = try! HDPrivateKey(seed: seed, network: .mainnet)
+            .derived(at: 44, hardened: true)
+            .derived(at: 0, hardened: true)
+            .derived(at: 0, hardened: true)
+            .derived(at: 1)
+            .derived(at: 19)
+        
+        let privKey = key.privateKey()
+        XCTAssertEqual(privKey.data.count, 32)
+        XCTAssertEqual(privKey.data.hex, "00f2c37dad54d1d2be57b06653ea655c6fd8eb3ca3f0b9671e036d50061d265b")
+        XCTAssertEqual(privKey.description, "KwFZ6jFtuvBu7w4R4x4WpzQgSSYTHLEw8Pr2PUkWjADkHJUPNDVg")
+        XCTAssertEqual(privKey.publicKey().description, "02a712f894d58baef44e4fbbc26ed6ca89487db1f17e944f9b45ca2ae666e99d72")
+        XCTAssertEqual(privKey.publicKey().toLegacy().description, "1DPUysR46jraybTwP3PfSbcBENeLScLxx")
+    }
 }