Merge pull request #220 from yenom/fix-privkey-derivation-bytes

🐛 Fix Private key derivation bug

Author: usatie

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 {

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")
+    }
 }