bip32_derive.go

package hdkey

import (
	"errors"
	"strconv"
	"strings"

	"github.com/btcsuite/btcutil/hdkeychain"
)

// DeriveFromPath derives extends key from bip32 path
func DerivePath(xprv *hdkeychain.ExtendedKey, path string) (*hdkeychain.ExtendedKey, error) {
	const (
		bip32MasterSymbol   = `m`
		bip32HardenedSymbol = `'`
		bip32PathDelimiter  = `/`
	)

	splitPath := strings.Split(path, bip32PathDelimiter)
	if splitPath[0] == bip32MasterSymbol {
		if xprv.ParentFingerprint() > 0 {
			return nil, errors.New("Derive private key from pubkey")
		}
		if len(splitPath) == 1 {
			return xprv, nil
		}
		splitPath = splitPath[1:]
	}

	next := xprv
	for _, item := range splitPath {
		if item == "" {
			continue
		}

		var err error
		var index uint64

		lastIndex := len(item) - 1
		if string(item[lastIndex]) == bip32HardenedSymbol {
			index, err = strconv.ParseUint(item[:lastIndex], 10, 32)
			index += hdkeychain.HardenedKeyStart
		} else {
			index, err = strconv.ParseUint(item, 10, 32)
		}

		if err != nil {
			return nil, errors.New("Not a positive integer")
		}

		next, err = next.Child(uint32(index))
		if err != nil {
			return nil, err
		}
	}
	return next, nil
}

bip32_derive_test.go

package hdkey

import (
	"reflect"
	"testing"

	"github.com/btcsuite/btcutil/hdkeychain"
)

func TestDerivePath(t *testing.T) {
	var mustFromSeed = func(seed string) *hdkeychain.ExtendedKey {
		res, err := hdkeychain.NewKeyFromString(seed)
		if err != nil {
			t.Errorf("Decode %s failed", seed)
			return nil
		}
		return res
	}

	type args struct {
		xprv *hdkeychain.ExtendedKey
		path string
	}
	tests := []struct {
		name    string
		args    args
		want    *hdkeychain.ExtendedKey
		wantErr bool
	}{
		{
			name: "valid",
			args: args{
				xprv: mustFromSeed("xprv9s21ZrQH143K2PunsF7pUyYnUBzJLRkg9RNYhVDRCGqJpKkAys6tH1LA49zw9t4jA61oh5AA6jCyXWTXbbLti6QSELWiTvcUTwKZcG4V8iA"),
				path: "m/44'/0'/0'/0",
			},
			want:    mustFromSeed("xprv9zc7gcUh94ThWj8kU4zkR3E8nKb5B7aNGYMW7ho3DqVdVfgfF2LZWUU2ykXLirVKxsjrC64AmopY23gZMV7t2gK582JWnpz8HVD73iPXD9P"),
			wantErr: false,
		},
		{
			name: "has redundant backslash",
			args: args{
				xprv: mustFromSeed("xprv9s21ZrQH143K2PunsF7pUyYnUBzJLRkg9RNYhVDRCGqJpKkAys6tH1LA49zw9t4jA61oh5AA6jCyXWTXbbLti6QSELWiTvcUTwKZcG4V8iA"),
				path: "m/44'/0'/0'/0/",
			},
			want:    mustFromSeed("xprv9zc7gcUh94ThWj8kU4zkR3E8nKb5B7aNGYMW7ho3DqVdVfgfF2LZWUU2ykXLirVKxsjrC64AmopY23gZMV7t2gK582JWnpz8HVD73iPXD9P"),
			wantErr: false,
		},
		{
			name: "only master symbol",
			args: args{
				xprv: mustFromSeed("xprv9s21ZrQH143K2PunsF7pUyYnUBzJLRkg9RNYhVDRCGqJpKkAys6tH1LA49zw9t4jA61oh5AA6jCyXWTXbbLti6QSELWiTvcUTwKZcG4V8iA"),
				path: "m",
			},
			want:    mustFromSeed("xprv9s21ZrQH143K2PunsF7pUyYnUBzJLRkg9RNYhVDRCGqJpKkAys6tH1LA49zw9t4jA61oh5AA6jCyXWTXbbLti6QSELWiTvcUTwKZcG4V8iA"),
			wantErr: false,
		},
		{
			name: "ErrDeriveNotMaster",
			args: args{
				xprv: mustFromSeed("xprvA19DxK9gkX44JVprp97UZEfVNCs587r8M6715rRaVkiy5azYHjDrJxMqeD8EWeSVupVz9NycS57gE17URk3TCNTdyMMuWw2VrXUg83iRfHN"),
				path: "m/44'/0'/0'/0",
			},
			want:    nil,
			wantErr: true,
		},
		{
			name: "invalid numberic",
			args: args{
				xprv: mustFromSeed("xprv9s21ZrQH143K3E3GR69HdDJZ3B6ncLa4sCdGeFJe4EoF1rnQSxmsAtqdQyBF1vZGga5VpCVjUZ6sba8RMihUzYVppAQiPAotbCkE6bmPGPF"),
				path: "abc/abc/abc/efg",
			},
			want:    nil,
			wantErr: true,
		},
		{
			name: "derive privkey from pubkey",
			args: args{
				xprv: mustFromSeed("xpub6FJ1fCip99xH43PykfeBhSwR2rh5WQtX8Tt3XSh7fWLZ71Rw1RNqtCLBPS2oGzWUoL4aBGPah2b92uV4E8wqUtp4HF17ZkWe3Yh8SMYhGYq"),
				path: `0'/0'/1`,
			},
			want:    nil,
			wantErr: true,
		},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got, err := DerivePath(tt.args.xprv, tt.args.path)
			if (err != nil) != tt.wantErr {
				t.Errorf("DerivePath() error = %v, wantErr %v", err, tt.wantErr)
				return
			}
			if !reflect.DeepEqual(got, tt.want) {
				t.Errorf("DerivePath() = %v, want %v", got, tt.want)
			}
		})
	}
}