chore(PrivateKey): remove the redundant methods of duplicated implementation

Author: sammyne

extended_key.go

@@ -17,9 +17,9 @@ type ExtendedKey interface {
 	// bound to it for private keys
 	AddressPubKeyHash() []byte
 	// 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
-	// extended key will be also be a public extended key.
+	// extended key is a private extended key, a private extended key will be
+	// derived.  Otherwise, the derived extended key will be also be a public
+	// extended key.
 	//
 	// When the index is greater to or equal than the HardenedKeyStart constant,
 	// the derived extended key will be a hardened extended key.  It is only
@@ -62,6 +62,9 @@ type ExtendedKey interface {
 	Neuter() (*PublicKey, error)
 	// ParentFingerprint returns a fingerprint of the parent extended key from
 	// which this one was derived.
+	//
+	// It's defined the be the first 32 bits of the key identifier as specified by
+	// https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#key-identifiers
 	ParentFingerprint() uint32
 	// Public converts the extended key to a btcec public key and returns it.
 	Public() (*btcec.PublicKey, error)

internal.go

@@ -32,7 +32,6 @@ func appendMeta(buf []byte, pub *PublicKey) []byte {
 // key string.
 // Note: the decoded key goes through format check only, no on-curve check
 func decodePublicKey(data58 string) (*PublicKey, error) {
-	//version, decoded, err := base58.CheckDecodeX(data58, VersionLen)
 	decoded, version, err := base58.CheckDecodeX(data58, VersionLen)
 	if nil != err {
 		return nil, err
@@ -49,11 +48,8 @@ func decodePublicKey(data58 string) (*PublicKey, error) {
 	// where the version has separated from decoded
 
 	// decompose the decoded payload into fields
-	//a, b := 0, VersionLen
-	//pub.Version = decoded[a:b]
 	pub.Version = version
 
-	//a, b = b, b+DepthLen
 	a, b := 0, DepthLen
 	pub.Level = decoded[a:b][0]
 

magics.go

@@ -7,7 +7,7 @@ const MagicLen = 4
 // Magic represents the buffer to hold the magic bytes.
 type Magic [MagicLen]byte
 
-// magic bytes as version prefix for serialization, and their application goes
+// magic bytes as version prefix for base58 encoding, and their application goes
 // as named.
 var (
 	MainNetPrivateKey = &Magic{0x04, 0x88, 0xad, 0xe4} // starts with xprv

master_key.go

@@ -23,33 +23,13 @@ func GenerateMasterKey(rand io.Reader, keyID Magic,
 		return nil, ErrNoEnoughEntropy
 	}
 
-	/*
-		// I = HMAC-SHA512(Key = "Bitcoin seed", Data = S)
-		hmac512 := hmac.New(sha512.New, masterKey)
-		hmac512.Write(seed)
-		I := hmac512.Sum(nil)
-
-		secretKey, chainCode := I[:len(I)/2], I[len(I)/2:]
-		// Ensure the key in usable.
-		if x := new(big.Int).SetBytes(secretKey); 0 == x.Sign() ||
-			x.Cmp(btcec.S256().N) >= 0 {
-			return nil, ErrUnusableSeed
-		}
-
-		// fingerprint of parent
-		parentFP := []byte{0x00, 0x00, 0x00, 0x00}
-
-		//return NewExtendedKey(keyID[:], secretKey, chainCode,
-		//	parentFP, 0, 0, true), nil
-
-		return NewPrivateKey(keyID[:], 0, parentFP, 0, chainCode, secretKey), nil
-	*/
+	// delegate the common derivation routine
 	return newMaster(seed, keyID)
 }
 
 // NewMasterKey creates a new master node for use in creating a hierarchical
 // deterministic key chain.  The seed must be between 128 and 512 bits and
-// should be generated by a cryptographically secure random generation source.
+// should be generated by a cryptographically secure random source.
 //
 // NOTE: There is an extremely small chance (< 1 in 2^127) the provided seed
 // will derive to an unusable secret key.  The ErrUnusable error will be
@@ -65,7 +45,9 @@ func NewMasterKey(seed []byte, keyID Magic) (*PrivateKey, error) {
 }
 
 // newMaster is helper function to derives a extended private key based on the
-// given valid seed and the provided keyID
+// given valid seed and the provided keyID.
+//
+// Official specification goes as https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#master-key-generation
 func newMaster(seed []byte, keyID Magic) (*PrivateKey, error) {
 	// I = HMAC-SHA512(Key = "Bitcoin seed", Data = S)
 	hmac512 := hmac.New(sha512.New, masterHMACKey)

private_key.go

@@ -15,7 +15,7 @@ import (
 	"github.com/sammyne/base58"
 )
 
-// PrivateKey represents an extended private key.
+// PrivateKey houses all the information of an extended private key.
 type PrivateKey struct {
 	PublicKey
 	Data    []byte
@@ -27,7 +27,7 @@ func (priv *PrivateKey) AddressPubKeyHash() []byte {
 	return btcutil.Hash160(priv.publicKeyData())
 }
 
-// Child  implements ExtendedKey
+// Child implements ExtendedKey
 func (priv *PrivateKey) Child(i uint32) (ExtendedKey, error) {
 	// Prevent derivation of children beyond the max allowed depth.
 	if priv.Level == math.MaxUint8 {
@@ -44,7 +44,7 @@ func (priv *PrivateKey) Child(i uint32) (ExtendedKey, error) {
 	data := make([]byte, KeyDataLen+ChildIndexLen)
 	if i < HardenedKeyStart { // normal
 		copy(data, priv.publicKeyData())
-	} else { // harden
+	} else { // harden, where 0x00 prefix plus 32-byte data
 		data[0] = 0x00
 		ReverseCopy(data[1:KeyDataLen], priv.Data)
 	}
@@ -60,7 +60,7 @@ func (priv *PrivateKey) Child(i uint32) (ExtendedKey, error) {
 	IL, chainCode := I[:len(I)/2], I[len(I)/2:]
 
 	// Both derived public or private keys rely on treating the left 32-byte
-	// sequence calculated above (Il) as a 256-bit integer that must be
+	// sequence calculated above (IL) as a 256-bit integer that must be
 	// within the valid range for a secp256k1 private key.  There is a small
 	// chance (< 1 in 2^127) this condition will not hold, and in that case,
 	// a child extended key can't be created for this index and the caller
@@ -74,7 +74,7 @@ func (priv *PrivateKey) Child(i uint32) (ExtendedKey, error) {
 	// Add the parent private key to the intermediate private key to
 	// derive the final child key.
 	//
-	// childKey = parse256(Il) + parenKey
+	// childKey = parse256(IL) + parenKey
 	k := new(big.Int).SetBytes(priv.Data)
 	z.Add(z, k)
 	z.Mod(z, secp256k1Curve.N)
@@ -88,21 +88,6 @@ func (priv *PrivateKey) Child(i uint32) (ExtendedKey, error) {
 		chainCode, childData), nil
 }
 
-// Depth implements ExtendedKey
-func (priv *PrivateKey) Depth() uint8 {
-	return priv.Level
-}
-
-// Hardened implements ExtendedKey
-func (priv *PrivateKey) Hardened() bool {
-	return priv.PublicKey.Hardened()
-}
-
-// Index implements ExtendedKey
-func (priv *PrivateKey) Index() uint32 {
-	return priv.PublicKey.Index()
-}
-
 // IsForNet implements ExtendedKey
 func (priv *PrivateKey) IsForNet(keyID Magic) bool {
 	return bytes.Equal(priv.Version, keyID[:])
@@ -135,11 +120,6 @@ func (priv *PrivateKey) Neuter() (*PublicKey, error) {
 	return &priv.PublicKey, nil
 }
 
-// ParentFingerprint implements ExtendedKey
-func (priv *PrivateKey) ParentFingerprint() uint32 {
-	return priv.PublicKey.ParentFingerprint()
-}
-
 // Public implements ExtendedKey
 func (priv *PrivateKey) Public() (*btcec.PublicKey, error) {
 	return btcec.ParsePubKey(priv.publicKeyData(), secp256k1Curve)
@@ -169,7 +149,7 @@ func (priv *PrivateKey) String() string {
 
 // ToECPrivate converts the extended key to a btcec private key and returns it.
 // As you might imagine this is only possible if the extended key is a private
-// extended key (as determined by the IsPrivate function).
+// extended key.
 func (priv *PrivateKey) ToECPrivate() *btcec.PrivateKey {
 	privKey, _ := btcec.PrivKeyFromBytes(secp256k1Curve, priv.Data)
 
@@ -216,14 +196,15 @@ func NewPrivateKey(version []byte, depth uint8, parentFP []byte, index uint32,
 // ParsePrivateKey a new extended private key instance out of a base58-encoded
 // extended key.
 func ParsePrivateKey(data58 string) (*PrivateKey, error) {
+	// decodePublicKey is applicable here too !!!
 	pub, err := decodePublicKey(data58)
 	if nil != err {
 		return nil, err
 	}
 
 	priv := &PrivateKey{
 		PublicKey: *pub,
-		Data:      pub.Data[1:],
+		Data:      pub.Data[1:], // simply trims out the 0x00 prefix
 	}
 	priv.Version = priv.PublicKey.Version
 	priv.PublicKey.Data, priv.PublicKey.Version = nil, nil