poor man's derivation path parser

Author: svanas

web3.bip32.pas

@@ -27,7 +27,10 @@
 interface
 
 uses
+  // Delphi
+  System.SysUtils,
   // web3
+  web3,
   web3.bip39;
 
 type
@@ -36,18 +39,24 @@ interface
   end;
 
   IPrivateKey = interface(IPublicKey)
+    function Data: TBytes;
     function NewChildKey(childIdx: UInt32): IPrivateKey;
     function PublicKey: IPublicKey;
   end;
 
+  IMasterKey = interface(IPrivateKey)
+    function GetChildKey(const path: string): IResult<IPrivateKey>;
+  end;
+
 // creates a new master extended key
-function master(const seed: web3.bip39.TSeed): IPrivateKey;
+function master(const seed: web3.bip39.TSeed): IMasterKey;
 
 implementation
 
 uses
   // Delphi
-  System.SysUtils,
+  System.Character,
+  System.Classes,
   // CryptoLib4Pascal
   ClpBigInteger,
   ClpBigIntegers,
@@ -163,6 +172,7 @@   TPrivateKey = class(TPublicKey, IPrivateKey)
   protected
     class function isPrivate: Boolean; override;
   public
+    function Data: TBytes;
     function NewChildKey(childIdx: UInt32): IPrivateKey;
     function PublicKey: IPublicKey;
   end;
@@ -174,6 +184,11 @@ class function TPrivateKey.isPrivate: Boolean;
   Result := True;
 end;
 
+function TPrivateKey.Data: TBytes;
+begin
+  Result := Self.keyData;
+end;
+
 // derives a child key from a given parent
 function TPrivateKey.NewChildKey(childIdx: UInt32): IPrivateKey;
 begin
@@ -215,10 +230,53 @@ function TPrivateKey.PublicKey: IPublicKey;
   );
 end;
 
-function master(const seed: web3.bip39.TSeed): IPrivateKey;
+type
+  TMasterKey = class(TPrivateKey, IMasterKey)
+  public
+    function GetChildKey(const path: string): IResult<IPrivateKey>;
+  end;
+
+function TMasterKey.GetChildKey(const path: string): IResult<IPrivateKey>;
+begin
+  const SL = TStringList.Create;
+  try
+    SL.Delimiter := '/';
+    SL.DelimitedText := path;
+    var K: IPrivateKey := Self;
+    for var I := 0 to Pred(SL.Count) do
+    begin
+      var S := SL[I].Trim;
+      if (I = 0) and S.Equals('m') then CONTINUE;
+      var C, E: UInt32; // child, error
+      Val(S, C, E);
+      if E <> 0 then
+      begin
+        if (S = '') or S[High(S)].IsDigit then
+        begin
+          Result := TResult<IPrivateKey>.Err(nil, 'invalid derivation path');
+          EXIT;
+        end;
+        Delete(S, High(S), 1);
+        Val(S, C, E);
+        if E <> 0 then
+        begin
+          Result := TResult<IPrivateKey>.Err(nil, 'invalid derivation path');
+          EXIT;
+        end;
+        C := C + firstHardenedChild;
+      end;
+      K := K.NewChildKey(C);
+    end;
+    Result := TResult<IPrivateKey>.Ok(K);
+  finally
+    SL.Free;
+  end;
+end;
+
+function master(const seed: web3.bip39.TSeed): IMasterKey;
 begin
   const digest = hmac_sha512(seed, TConverters.ConvertStringToBytes('Bitcoin seed', TEncoding.UTF8));
-  Result := TPrivateKey.Create(
+  Result := TMasterKey.Create(
     privateWalletVersion, // version
     Copy(digest, 0, 32),  // key data
     Copy(digest, 32, 32), // chain code

web3.bip32.tests.json

@@ -5,27 +5,27 @@
         "pubKey": "xpub661MyMwAqRbcFtXgS5sYJABqqG9YLmC4Q1Rdap9gSE8NqtwybGhePY2gZ29ESFjqJoCu1Rupje8YtGqsefD265TMg7usUDFdp6W1EGMcet8",
         "children": [
             {
-                "path": 2147483648,
+                "path": "m/0H",
                 "privKey": "xprv9uHRZZhk6KAJC1avXpDAp4MDc3sQKNxDiPvvkX8Br5ngLNv1TxvUxt4cV1rGL5hj6KCesnDYUhd7oWgT11eZG7XnxHrnYeSvkzY7d2bhkJ7",
                 "pubKey": "xpub68Gmy5EdvgibQVfPdqkBBCHxA5htiqg55crXYuXoQRKfDBFA1WEjWgP6LHhwBZeNK1VTsfTFUHCdrfp1bgwQ9xv5ski8PX9rL2dZXvgGDnw"
             },
             {
-                "path": 1,
+                "path": "m/0H/1",
                 "privKey": "xprv9wTYmMFdV23N2TdNG573QoEsfRrWKQgWeibmLntzniatZvR9BmLnvSxqu53Kw1UmYPxLgboyZQaXwTCg8MSY3H2EU4pWcQDnRnrVA1xe8fs",
                 "pubKey": "xpub6ASuArnXKPbfEwhqN6e3mwBcDTgzisQN1wXN9BJcM47sSikHjJf3UFHKkNAWbWMiGj7Wf5uMash7SyYq527Hqck2AxYysAA7xmALppuCkwQ"
             },
             {
-                "path": 2147483650,
+                "path": "m/0H/1/2H",
                 "privKey": "xprv9z4pot5VBttmtdRTWfWQmoH1taj2axGVzFqSb8C9xaxKymcFzXBDptWmT7FwuEzG3ryjH4ktypQSAewRiNMjANTtpgP4mLTj34bhnZX7UiM",
                 "pubKey": "xpub6D4BDPcP2GT577Vvch3R8wDkScZWzQzMMUm3PWbmWvVJrZwQY4VUNgqFJPMM3No2dFDFGTsxxpG5uJh7n7epu4trkrX7x7DogT5Uv6fcLW5"
             },
             {
-                "path": 2,
+                "path": "m/0H/1/2H/2",
                 "privKey": "xprvA2JDeKCSNNZky6uBCviVfJSKyQ1mDYahRjijr5idH2WwLsEd4Hsb2Tyh8RfQMuPh7f7RtyzTtdrbdqqsunu5Mm3wDvUAKRHSC34sJ7in334",
                 "pubKey": "xpub6FHa3pjLCk84BayeJxFW2SP4XRrFd1JYnxeLeU8EqN3vDfZmbqBqaGJAyiLjTAwm6ZLRQUMv1ZACTj37sR62cfN7fe5JnJ7dh8zL4fiyLHV"
             },
             {
-                "path": 1000000000,
+                "path": "m/0H/1/2H/2/1000000000",
                 "privKey": "xprvA41z7zogVVwxVSgdKUHDy1SKmdb533PjDz7J6N6mV6uS3ze1ai8FHa8kmHScGpWmj4WggLyQjgPie1rFSruoUihUZREPSL39UNdE3BBDu76",
                 "pubKey": "xpub6H1LXWLaKsWFhvm6RVpEL9P4KfRZSW7abD2ttkWP3SSQvnyA8FSVqNTEcYFgJS2UaFcxupHiYkro49S8yGasTvXEYBVPamhGW6cFJodrTHy"
             }
@@ -37,27 +37,27 @@
         "pubKey": "xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB",
         "children": [
             {
-                "path": 0,
+                "path": "m/0",
                 "privKey": "xprv9vHkqa6EV4sPZHYqZznhT2NPtPCjKuDKGY38FBWLvgaDx45zo9WQRUT3dKYnjwih2yJD9mkrocEZXo1ex8G81dwSM1fwqWpWkeS3v86pgKt",
                 "pubKey": "xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH"
             },
             {
-                "path": 4294967295,
+                "path": "m/0/2147483647H",
                 "privKey": "xprv9wSp6B7kry3Vj9m1zSnLvN3xH8RdsPP1Mh7fAaR7aRLcQMKTR2vidYEeEg2mUCTAwCd6vnxVrcjfy2kRgVsFawNzmjuHc2YmYRmagcEPdU9",
                 "pubKey": "xpub6ASAVgeehLbnwdqV6UKMHVzgqAG8Gr6riv3Fxxpj8ksbH9ebxaEyBLZ85ySDhKiLDBrQSARLq1uNRts8RuJiHjaDMBU4Zn9h8LZNnBC5y4a"
             },
             {
-                "path": 1,
+                "path": "m/0/2147483647H/1",
                 "privKey": "xprv9zFnWC6h2cLgpmSA46vutJzBcfJ8yaJGg8cX1e5StJh45BBciYTRXSd25UEPVuesF9yog62tGAQtHjXajPPdbRCHuWS6T8XA2ECKADdw4Ef",
                 "pubKey": "xpub6DF8uhdarytz3FWdA8TvFSvvAh8dP3283MY7p2V4SeE2wyWmG5mg5EwVvmdMVCQcoNJxGoWaU9DCWh89LojfZ537wTfunKau47EL2dhHKon"
             },
             {
-                "path": 4294967294,
+                "path": "m/0/2147483647H/1/2147483646H",
                 "privKey": "xprvA1RpRA33e1JQ7ifknakTFpgNXPmW2YvmhqLQYMmrj4xJXXWYpDPS3xz7iAxn8L39njGVyuoseXzU6rcxFLJ8HFsTjSyQbLYnMpCqE2VbFWc",
                 "pubKey": "xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL"
             },
             {
-                "path": 2,
+                "path": "m/0/2147483647H/1/2147483646H/2",
                 "privKey": "xprvA2nrNbFZABcdryreWet9Ea4LvTJcGsqrMzxHx98MMrotbir7yrKCEXw7nadnHM8Dq38EGfSh6dqA9QWTyefMLEcBYJUuekgW4BYPJcr9E7j",
                 "pubKey": "xpub6FnCn6nSzZAw5Tw7cgR9bi15UV96gLZhjDstkXXxvCLsUXBGXPdSnLFbdpq8p9HmGsApME5hQTZ3emM2rnY5agb9rXpVGyy3bdW6EEgAtqt"
             }
@@ -69,7 +69,7 @@
         "pubKey": "xpub661MyMwAqRbcEZVB4dScxMAdx6d4nFc9nvyvH3v4gJL378CSRZiYmhRoP7mBy6gSPSCYk6SzXPTf3ND1cZAceL7SfJ1Z3GC8vBgp2epUt13",
         "children": [
             {
-                "path": 2147483648,
+                "path": "m/0H",
                 "privKey": "xprv9uPDJpEQgRQfDcW7BkF7eTya6RPxXeJCqCJGHuCJ4GiRVLzkTXBAJMu2qaMWPrS7AANYqdq6vcBcBUdJCVVFceUvJFjaPdGZ2y9WACViL4L",
                 "pubKey": "xpub68NZiKmJWnxxS6aaHmn81bvJeTESw724CRDs6HbuccFQN9Ku14VQrADWgqbhhTHBaohPX4CjNLf9fq9MYo6oDaPPLPxSb7gwQN3ih19Zm4Y"
             }            
@@ -81,12 +81,12 @@
         "pubKey": "xpub661MyMwAqRbcGczjuMoRm6dXaLDEhW1u34gKenbeYqAix21mdUKJyuyu5F1rzYGVxyL6tmgBUAEPrEz92mBXjByMRiJdba9wpnN37RLLAXa",
         "children": [
             {
-                "path": 2147483648,
+                "path": "m/0H",
                 "privKey": "xprv9vB7xEWwNp9kh1wQRfCCQMnZUEG21LpbR9NPCNN1dwhiZkjjeGRnaALmPXCX7SgjFTiCTT6bXes17boXtjq3xLpcDjzEuGLQBM5ohqkao9G",
                 "pubKey": "xpub69AUMk3qDBi3uW1sXgjCmVjJ2G6WQoYSnNHyzkmdCHEhSZ4tBok37xfFEqHd2AddP56Tqp4o56AePAgCjYdvpW2PU2jbUPFKsav5ut6Ch1m"
             },
             {
-                "path": 2147483649,
+                "path": "m/0H/1H",
                 "privKey": "xprv9xJocDuwtYCMNAo3Zw76WENQeAS6WGXQ55RCy7tDJ8oALr4FWkuVoHJeHVAcAqiZLE7Je3vZJHxspZdFHfnBEjHqU5hG1Jaj32dVoS6XLT1",
                 "pubKey": "xpub6BJA1jSqiukeaesWfxe6sNK9CCGaujFFSJLomWHprUL9DePQ4JDkM5d88n49sMGJxrhpjazuXYWdMf17C9T5XnxkopaeS7jGk1GyyVziaMt"
             }                              

web3.bip32.tests.pas

@@ -70,20 +70,21 @@ procedure TTests.TestCase;
       for var vector in vectors as TJsonArray do
       begin
         const seed = '0x' + web3.json.getPropAsStr(vector, 'seed');
-        var parent := web3.bip32.master(web3.utils.fromHex(seed));
+        const master = web3.bip32.master(web3.utils.fromHex(seed));
         var privKey := web3.json.getPropAsStr(vector, 'privKey');
-        Assert.AreEqual(parent.ToString, privKey);
+        Assert.AreEqual(master.ToString, privKey);
         var pubKey := web3.json.getPropAsStr(vector, 'pubKey');
-        Assert.AreEqual(parent.PublicKey.ToString, pubKey);
+        Assert.AreEqual(master.PublicKey.ToString, pubKey);
         const children = web3.json.getPropAsArr(vector, 'children');
         for var child in children do
         begin
-          const path = web3.json.getPropAsBigInt(child, 'path');
-          parent := parent.NewChildKey(path.AsCardinal);
+          const path = web3.json.getPropAsStr(child, 'path');
+          const key = master.GetChildKey(path);
+          if key.IsErr then Assert.Fail(key.Error.Message);
           privKey := web3.json.getPropAsStr(child, 'privKey');
-          Assert.AreEqual(parent.ToString, privKey);
+          Assert.AreEqual(key.Value.ToString, privKey);
           pubKey := web3.json.getPropAsStr(child, 'pubKey');
-          Assert.AreEqual(parent.PublicKey.ToString, pubKey);
+          Assert.AreEqual(key.Value.PublicKey.ToString, pubKey);
         end;
       end;
     finally