--- /dev/null
+package chainkd
+
+import (
+ "crypto/hmac"
+ "crypto/rand"
+ "crypto/sha512"
+ "io"
+
+ "github.com/vapor/crypto/ed25519"
+ "github.com/vapor/crypto/ed25519/ecmath"
+)
+
+type (
+ //XPrv external private key
+ XPrv [64]byte
+ //XPub external public key
+ XPub [64]byte
+)
+
+// NewXPrv takes a source of random bytes and produces a new XPrv.
+// If r is nil, crypto/rand.Reader is used.
+func NewXPrv(r io.Reader) (xprv XPrv, err error) {
+ if r == nil {
+ r = rand.Reader
+ }
+ var entropy [64]byte
+ _, err = io.ReadFull(r, entropy[:])
+ if err != nil {
+ return xprv, err
+ }
+ return RootXPrv(entropy[:]), nil
+}
+
+// RootXPrv takes a seed binary string and produces a new xprv.
+func RootXPrv(seed []byte) (xprv XPrv) {
+ h := hmac.New(sha512.New, []byte{'R', 'o', 'o', 't'})
+ h.Write(seed)
+ h.Sum(xprv[:0])
+ pruneRootScalar(xprv[:32])
+ return
+}
+
+// XPub derives an extended public key from a given xprv.
+func (xprv XPrv) XPub() (xpub XPub) {
+ var scalar ecmath.Scalar
+ copy(scalar[:], xprv[:32])
+
+ var P ecmath.Point
+ P.ScMulBase(&scalar)
+ buf := P.Encode()
+
+ copy(xpub[:32], buf[:])
+ copy(xpub[32:], xprv[32:])
+
+ return
+}
+
+// Child derives a child xprv based on `selector` string and `hardened` flag.
+// If `hardened` is false, child xpub can be derived independently
+// from the parent xpub without using the parent xprv.
+// If `hardened` is true, child key can only be derived from the parent xprv.
+func (xprv XPrv) Child(sel []byte, hardened bool) XPrv {
+ if hardened {
+ return xprv.hardenedChild(sel)
+ }
+ return xprv.nonhardenedChild(sel)
+}
+
+func (xprv XPrv) hardenedChild(sel []byte) (res XPrv) {
+ h := hmac.New(sha512.New, xprv[32:])
+ h.Write([]byte{'H'})
+ h.Write(xprv[:32])
+ h.Write(sel)
+ h.Sum(res[:0])
+ pruneRootScalar(res[:32])
+ return
+}
+
+func (xprv XPrv) nonhardenedChild(sel []byte) (res XPrv) {
+ xpub := xprv.XPub()
+
+ h := hmac.New(sha512.New, xpub[32:])
+ h.Write([]byte{'N'})
+ h.Write(xpub[:32])
+ h.Write(sel)
+ h.Sum(res[:0])
+
+ pruneIntermediateScalar(res[:32])
+
+ // Unrolled the following loop:
+ // var carry int
+ // carry = 0
+ // for i := 0; i < 32; i++ {
+ // sum := int(xprv[i]) + int(res[i]) + carry
+ // res[i] = byte(sum & 0xff)
+ // carry = (sum >> 8)
+ // }
+
+ sum := int(0)
+
+ sum = int(xprv[0]) + int(res[0]) + (sum >> 8)
+ res[0] = byte(sum & 0xff)
+ sum = int(xprv[1]) + int(res[1]) + (sum >> 8)
+ res[1] = byte(sum & 0xff)
+ sum = int(xprv[2]) + int(res[2]) + (sum >> 8)
+ res[2] = byte(sum & 0xff)
+ sum = int(xprv[3]) + int(res[3]) + (sum >> 8)
+ res[3] = byte(sum & 0xff)
+ sum = int(xprv[4]) + int(res[4]) + (sum >> 8)
+ res[4] = byte(sum & 0xff)
+ sum = int(xprv[5]) + int(res[5]) + (sum >> 8)
+ res[5] = byte(sum & 0xff)
+ sum = int(xprv[6]) + int(res[6]) + (sum >> 8)
+ res[6] = byte(sum & 0xff)
+ sum = int(xprv[7]) + int(res[7]) + (sum >> 8)
+ res[7] = byte(sum & 0xff)
+ sum = int(xprv[8]) + int(res[8]) + (sum >> 8)
+ res[8] = byte(sum & 0xff)
+ sum = int(xprv[9]) + int(res[9]) + (sum >> 8)
+ res[9] = byte(sum & 0xff)
+ sum = int(xprv[10]) + int(res[10]) + (sum >> 8)
+ res[10] = byte(sum & 0xff)
+ sum = int(xprv[11]) + int(res[11]) + (sum >> 8)
+ res[11] = byte(sum & 0xff)
+ sum = int(xprv[12]) + int(res[12]) + (sum >> 8)
+ res[12] = byte(sum & 0xff)
+ sum = int(xprv[13]) + int(res[13]) + (sum >> 8)
+ res[13] = byte(sum & 0xff)
+ sum = int(xprv[14]) + int(res[14]) + (sum >> 8)
+ res[14] = byte(sum & 0xff)
+ sum = int(xprv[15]) + int(res[15]) + (sum >> 8)
+ res[15] = byte(sum & 0xff)
+ sum = int(xprv[16]) + int(res[16]) + (sum >> 8)
+ res[16] = byte(sum & 0xff)
+ sum = int(xprv[17]) + int(res[17]) + (sum >> 8)
+ res[17] = byte(sum & 0xff)
+ sum = int(xprv[18]) + int(res[18]) + (sum >> 8)
+ res[18] = byte(sum & 0xff)
+ sum = int(xprv[19]) + int(res[19]) + (sum >> 8)
+ res[19] = byte(sum & 0xff)
+ sum = int(xprv[20]) + int(res[20]) + (sum >> 8)
+ res[20] = byte(sum & 0xff)
+ sum = int(xprv[21]) + int(res[21]) + (sum >> 8)
+ res[21] = byte(sum & 0xff)
+ sum = int(xprv[22]) + int(res[22]) + (sum >> 8)
+ res[22] = byte(sum & 0xff)
+ sum = int(xprv[23]) + int(res[23]) + (sum >> 8)
+ res[23] = byte(sum & 0xff)
+ sum = int(xprv[24]) + int(res[24]) + (sum >> 8)
+ res[24] = byte(sum & 0xff)
+ sum = int(xprv[25]) + int(res[25]) + (sum >> 8)
+ res[25] = byte(sum & 0xff)
+ sum = int(xprv[26]) + int(res[26]) + (sum >> 8)
+ res[26] = byte(sum & 0xff)
+ sum = int(xprv[27]) + int(res[27]) + (sum >> 8)
+ res[27] = byte(sum & 0xff)
+ sum = int(xprv[28]) + int(res[28]) + (sum >> 8)
+ res[28] = byte(sum & 0xff)
+ sum = int(xprv[29]) + int(res[29]) + (sum >> 8)
+ res[29] = byte(sum & 0xff)
+ sum = int(xprv[30]) + int(res[30]) + (sum >> 8)
+ res[30] = byte(sum & 0xff)
+ sum = int(xprv[31]) + int(res[31]) + (sum >> 8)
+ res[31] = byte(sum & 0xff)
+
+ if (sum >> 8) != 0 {
+ panic("sum does not fit in 256-bit int")
+ }
+ return
+}
+
+// Child derives a child xpub based on `selector` string.
+// The corresponding child xprv can be derived from the parent xprv
+// using non-hardened derivation: `parentxprv.Child(sel, false)`.
+func (xpub XPub) Child(sel []byte) (res XPub) {
+ h := hmac.New(sha512.New, xpub[32:])
+ h.Write([]byte{'N'})
+ h.Write(xpub[:32])
+ h.Write(sel)
+ h.Sum(res[:0])
+
+ pruneIntermediateScalar(res[:32])
+
+ var (
+ f ecmath.Scalar
+ F ecmath.Point
+ )
+ copy(f[:], res[:32])
+ F.ScMulBase(&f)
+
+ var (
+ pubkey [32]byte
+ P ecmath.Point
+ )
+ copy(pubkey[:], xpub[:32])
+ _, ok := P.Decode(pubkey)
+ if !ok {
+ panic("XPub should have been validated on initialization")
+ }
+
+ P.Add(&P, &F)
+ pubkey = P.Encode()
+ copy(res[:32], pubkey[:])
+
+ return
+}
+
+// Derive generates a child xprv by recursively deriving
+// non-hardened child xprvs over the list of selectors:
+// `Derive([a,b,c,...]) == Child(a).Child(b).Child(c)...`
+func (xprv XPrv) Derive(path [][]byte) XPrv {
+ res := xprv
+ for _, p := range path {
+ res = res.Child(p, false)
+ }
+ return res
+}
+
+// Derive generates a child xpub by recursively deriving
+// non-hardened child xpubs over the list of selectors:
+// `Derive([a,b,c,...]) == Child(a).Child(b).Child(c)...`
+func (xpub XPub) Derive(path [][]byte) XPub {
+ res := xpub
+ for _, p := range path {
+ res = res.Child(p)
+ }
+ return res
+}
+
+// Sign creates an EdDSA signature using expanded private key
+// derived from the xprv.
+func (xprv XPrv) Sign(msg []byte) []byte {
+ return Ed25519InnerSign(xprv.ExpandedPrivateKey(), msg)
+}
+
+// Verify checks an EdDSA signature using public key
+// extracted from the first 32 bytes of the xpub.
+func (xpub XPub) Verify(msg []byte, sig []byte) bool {
+ return ed25519.Verify(xpub.PublicKey(), msg, sig)
+}
+
+// ExpandedPrivateKey generates a 64-byte key where
+// the first half is the scalar copied from xprv,
+// and the second half is the `prefix` is generated via PRF
+// from the xprv.
+func (xprv XPrv) ExpandedPrivateKey() ExpandedPrivateKey {
+ var res [64]byte
+ h := hmac.New(sha512.New, []byte{'E', 'x', 'p', 'a', 'n', 'd'})
+ h.Write(xprv[:])
+ h.Sum(res[:0])
+ copy(res[:32], xprv[:32])
+ return res[:]
+}
+
+// PublicKey extracts the ed25519 public key from an xpub.
+func (xpub XPub) PublicKey() ed25519.PublicKey {
+ return ed25519.PublicKey(xpub[:32])
+}
+
+// s must be >= 32 bytes long and gets rewritten in place.
+// This is NOT the same pruning as in Ed25519: it additionally clears the third
+// highest bit to ensure subkeys do not overflow the second highest bit.
+func pruneRootScalar(s []byte) {
+ s[0] &= 248
+ s[31] &= 31 // clear top 3 bits
+ s[31] |= 64 // set second highest bit
+}
+
+// Clears lowest 3 bits and highest 23 bits of `f`.
+func pruneIntermediateScalar(f []byte) {
+ f[0] &= 248 // clear bottom 3 bits
+ f[29] &= 1 // clear 7 high bits
+ f[30] = 0 // clear 8 bits
+ f[31] = 0 // clear 8 bits
+}
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