hdkeychain: Use direct hashes and remove dcrutil dep

This change replaces usage of chainhash (which is intended solely for
transaction and blocks) and dcrutil.Hash160 (used in scripts for
hashing redeem scripts and pubkeys) with direct calls to each hashing
function from dcrd's crypto subpackages.  This improves clarity and
shortens the transitive package imports.  Notably, dcrutil and
everything it depends on is no longer transitively imported when
importing the hdkeychain package.

hdkeychain/extendedkey.go

@@ -20,9 +20,9 @@ import (
 	"math/big"
 
 	"github.com/decred/base58"
-	"github.com/decred/dcrd/chaincfg/chainhash"
+	"github.com/decred/dcrd/crypto/blake256"
+	"github.com/decred/dcrd/crypto/ripemd160"
 	"github.com/decred/dcrd/dcrec/secp256k1/v3"
-	"github.com/decred/dcrd/dcrutil/v3"
 )
 
 const (
@@ -197,6 +197,21 @@ func (k *ExtendedKey) ParentFingerprint() uint32 {
 	return binary.BigEndian.Uint32(k.parentFP)
 }
 
+// hash160 returns RIPEMD160(BLAKE256(v)).
+func hash160(v []byte) []byte {
+	blake256Hash := blake256.Sum256(v)
+	h := ripemd160.New()
+	h.Write(blake256Hash[:])
+	return h.Sum(nil)
+}
+
+// doubleBlake256Cksum returns the first four bytes of BLAKE256(BLAKE256(v)).
+func doubleBlake256Cksum(v []byte) []byte {
+	first := blake256.Sum256(v)
+	second := blake256.Sum256(first[:])
+	return second[:4]
+}
+
 // Child returns a derived child extended key at the given index.  When this
 // extended key is a private extended key (as determined by the IsPrivate
 // function), a private extended key will be derived.  Otherwise, the derived
@@ -332,7 +347,7 @@ func (k *ExtendedKey) Child(i uint32) (*ExtendedKey, error) {
 
 	// The fingerprint of the parent for the derived child is the first 4
 	// bytes of the RIPEMD160(BLAKE256(parentPubKey)).
-	parentFP := dcrutil.Hash160(k.pubKeyBytes())[:4]
+	parentFP := hash160(k.pubKeyBytes())[:4]
 	return newExtendedKey(k.privVer, k.pubVer, childKey, childChainCode,
 		parentFP, k.depth+1, i, isPrivate), nil
 }
@@ -419,7 +434,7 @@ func (k *ExtendedKey) String() string {
 		serializedBytes = append(serializedBytes, k.pubKeyBytes()...)
 	}
 
-	checkSum := chainhash.HashB(chainhash.HashB(serializedBytes))[:4]
+	checkSum := doubleBlake256Cksum(serializedBytes)
 	serializedBytes = append(serializedBytes, checkSum...)
 	return base58.Encode(serializedBytes)
 }
@@ -503,7 +518,7 @@ func NewKeyFromString(key string, net NetworkParams) (*ExtendedKey, error) {
 	// Split the payload and checksum up and ensure the checksum matches.
 	payload := decoded[:len(decoded)-4]
 	checkSum := decoded[len(decoded)-4:]
-	expectedCheckSum := chainhash.HashB(chainhash.HashB(payload))[:4]
+	expectedCheckSum := doubleBlake256Cksum(payload)
 	if !bytes.Equal(checkSum, expectedCheckSum) {
 		return nil, ErrBadChecksum
 	}

hdkeychain/go.mod

@@ -4,8 +4,9 @@ go 1.11
 
 require (
 	github.com/decred/base58 v1.0.2
-	github.com/decred/dcrd/chaincfg/chainhash v1.0.2
 	github.com/decred/dcrd/chaincfg/v3 v3.0.0-20200215031403-6b2ce76f0986
+	github.com/decred/dcrd/crypto/blake256 v1.0.0
+	github.com/decred/dcrd/crypto/ripemd160 v1.0.0
 	github.com/decred/dcrd/dcrec v1.0.0
 	github.com/decred/dcrd/dcrec/secp256k1/v3 v3.0.0-20200215031403-6b2ce76f0986
 	github.com/decred/dcrd/dcrutil/v3 v3.0.0-20200215031403-6b2ce76f0986