dex/keygen: use ChildBIP32Std for extended key derivation

This updates the GenDeepChild helper, which is used in both client/core
to setup DEX account keys from the app seed, and in client/asset/eth to
derive the account private key from the wallet seed.

This is especially in the eth key derivation, where the intent is to
follow BIP44 with the path m/44'/60'/0'/0/0, which requires generating
child keys as per BIP32 strictly.

For generating DEX account keys from the app seed, it is also good from
a standardness point of view to use strict BIP32 derivation.  The legacy
derivation is only required for Decred wallets for compatibility.

dex/keygen/keygen.go

@@ -28,7 +28,7 @@ func GenDeepChild(seed []byte, kids []uint32) (*hdkeychain.ExtendedKey, error) {
 		err := hdkeychain.ErrInvalidChild
 		for err == hdkeychain.ErrInvalidChild {
 			var kid *hdkeychain.ExtendedKey
-			kid, err = parent.Child(childIdx)
+			kid, err = parent.ChildBIP32Std(childIdx)
 			if err == nil {
 				return kid, nil
 			}

dex/keygen/keygen_test.go

@@ -16,17 +16,17 @@ func TestGenDeepChild(t *testing.T) {
 		t.Fatalf("error getting HD keychain root: %v", err)
 	}
 
-	expectedChild, err := root.Child(1)
+	expectedChild, err := root.ChildBIP32Std(1)
 	if err != nil {
 		t.Fatalf("error deriving child: %v", err)
 	}
 
-	expectedChild, err = expectedChild.Child(2)
+	expectedChild, err = expectedChild.ChildBIP32Std(2)
 	if err != nil {
 		t.Fatalf("error deriving child: %v", err)
 	}
 
-	expectedChild, err = expectedChild.Child(3)
+	expectedChild, err = expectedChild.ChildBIP32Std(3)
 	if err != nil {
 		t.Fatalf("error deriving child: %v", err)
 	}

go.mod

@@ -2,6 +2,8 @@ module decred.org/dcrdex
 
 go 1.16
 
+replace github.com/decred/dcrd/hdkeychain/v3 => github.com/chappjc/dcrd/hdkeychain/v3 v3.0.0-20211209152155-a5ed31b4792c
+
 require (
 	decred.org/dcrwallet/v2 v2.0.0-20211206163037-9537363becbb
 	github.com/btcsuite/btcd v0.22.0-beta.0.20211026140004-31791ba4dc6e

go.sum

@@ -118,6 +118,8 @@ github.com/cespare/xxhash v1.1.0 h1:a6HrQnmkObjyL+Gs60czilIUGqrzKutQD6XZog3p+ko=
 github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
 github.com/cespare/xxhash/v2 v2.1.1 h1:6MnRN8NT7+YBpUIWxHtefFZOKTAPgGjpQSxqLNn0+qY=
 github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
+github.com/chappjc/dcrd/hdkeychain/v3 v3.0.0-20211209152155-a5ed31b4792c h1:38QutUk71CWIJS/R499su//6VABu3sDP7lD37AvcUes=
+github.com/chappjc/dcrd/hdkeychain/v3 v3.0.0-20211209152155-a5ed31b4792c/go.mod h1:rDCdqwGkcTfEyRheG1g8Wc38appT2C9+D1XTlLy21lo=
 github.com/chzyer/logex v1.1.10/go.mod h1:+Ywpsq7O8HXn0nuIou7OrIPyXbp3wmkHB+jjWRnGsAI=
 github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5PlCu98SY8svDHJxuZscDgtXS6KTTbou5AhLI=
 github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMnBNeIyt5eFwwo7qiLfzFZmjNmxjkiQlU=
@@ -185,8 +187,6 @@ github.com/decred/dcrd/dcrutil/v4 v4.0.0/go.mod h1:QQpX5WVH3/ixVtiW15xZMe+neugXX
 github.com/decred/dcrd/gcs/v3 v3.0.0-20210916172859-ca03de05ecd0/go.mod h1:cfMmjV1ArvX+nemwwq1texW5pD0wrUt5TEw4IYuTmMM=
 github.com/decred/dcrd/gcs/v3 v3.0.0 h1:MjWevhoAzKENUgpaJAbZkJlKDN4HIz2nR/i3laZAT5c=
 github.com/decred/dcrd/gcs/v3 v3.0.0/go.mod h1:/OVb/rYrAz4TCtxcPneYfBs0+YI1pGIp8RA6RUNqOp4=
-github.com/decred/dcrd/hdkeychain/v3 v3.0.1 h1:wvfHa3VY8YW1sB2TzXipCehO6N0u1H6rSsNAYtEE9VY=
-github.com/decred/dcrd/hdkeychain/v3 v3.0.1/go.mod h1:rDCdqwGkcTfEyRheG1g8Wc38appT2C9+D1XTlLy21lo=
 github.com/decred/dcrd/lru v1.0.0/go.mod h1:mxKOwFd7lFjN2GZYsiz/ecgqR6kkYAl+0pz0tEMk218=
 github.com/decred/dcrd/lru v1.1.0 h1:QwT6v8LFKOL3xQ3qtucgRk4pdiawrxIfCbUXWpm+JL4=
 github.com/decred/dcrd/lru v1.1.0/go.mod h1:mxKOwFd7lFjN2GZYsiz/ecgqR6kkYAl+0pz0tEMk218=