func TestPubKeys(t *testing.T) {
	for _, test := range pubKeyTests {
		pk, err := btcec.ParsePubKey(test.key, btcec.S256())
		if err != nil {
			if test.isValid {
				t.Errorf("%s pubkey failed when shouldn't %v",
					test.name, err)
			}
			continue
		}
		if !test.isValid {
			t.Errorf("%s counted as valid when it should fail",
				test.name)
			continue
		}
		var pkStr []byte
		switch test.format {
		case btcec.TstPubkeyUncompressed:
			pkStr = (*btcec.PublicKey)(pk).SerializeUncompressed()
		case btcec.TstPubkeyCompressed:
			pkStr = (*btcec.PublicKey)(pk).SerializeCompressed()
		case btcec.TstPubkeyHybrid:
			pkStr = (*btcec.PublicKey)(pk).SerializeHybrid()
		}
		if !bytes.Equal(test.key, pkStr) {
			t.Errorf("%s pubkey: serialized keys do not match.",
				test.name)
			spew.Dump(test.key)
			spew.Dump(pkStr)
		}
	}
}
// NewKeyFromString returns a new extended key instance from a base58-encoded
// extended key.
func NewKeyFromString(key string) (*ExtendedKey, error) {
	// The base58-decoded extended key must consist of a serialized payload
	// plus an additional 4 bytes for the checksum.
	decoded := base58.Decode(key)
	if len(decoded) != serializedKeyLen+4 {
		return nil, ErrInvalidKeyLen
	}

	// The serialized format is:
	//   version (4) || depth (1) || parent fingerprint (4)) ||
	//   child num (4) || chain code (32) || key data (33) || checksum (4)

	// Split the payload and checksum up and ensure the checksum matches.
	payload := decoded[:len(decoded)-4]
	checkSum := decoded[len(decoded)-4:]
	expectedCheckSum := wire.DoubleSha256(payload)[:4]
	if !bytes.Equal(checkSum, expectedCheckSum) {
		return nil, ErrBadChecksum
	}

	// Deserialize each of the payload fields.
	version := payload[:4]
	depth := uint16(payload[4:5][0])
	parentFP := payload[5:9]
	childNum := binary.BigEndian.Uint32(payload[9:13])
	chainCode := payload[13:45]
	keyData := payload[45:78]

	// The key data is a private key if it starts with 0x00.  Serialized
	// compressed pubkeys either start with 0x02 or 0x03.
	isPrivate := keyData[0] == 0x00
	if isPrivate {
		// Ensure the private key is valid.  It must be within the range
		// of the order of the secp256k1 curve and not be 0.
		keyData = keyData[1:]
		keyNum := new(big.Int).SetBytes(keyData)
		if keyNum.Cmp(btcec.S256().N) >= 0 || keyNum.Sign() == 0 {
			return nil, ErrUnusableSeed
		}
	} else {
		// Ensure the public key parses correctly and is actually on the
		// secp256k1 curve.
		_, err := btcec.ParsePubKey(keyData, btcec.S256())
		if err != nil {
			return nil, err
		}
	}

	return newExtendedKey(version, keyData, chainCode, parentFP, depth,
		childNum, isPrivate), nil
}
// This example demonstrates encrypting a message for a public key that is first
// parsed from raw bytes, then decrypting it using the corresponding private key.
func Example_encryptMessage() {
	// Decode the hex-encoded pubkey of the recipient.
	pubKeyBytes, err := hex.DecodeString("04115c42e757b2efb7671c578530ec191a1" +
		"359381e6a71127a9d37c486fd30dae57e76dc58f693bd7e7010358ce6b165e483a29" +
		"21010db67ac11b1b51b651953d2") // uncompressed pubkey
	if err != nil {
		fmt.Println(err)
		return
	}
	pubKey, err := btcec.ParsePubKey(pubKeyBytes, btcec.S256())
	if err != nil {
		fmt.Println(err)
		return
	}

	// Encrypt a message decryptable by the private key corresponding to pubKey
	message := "test message"
	ciphertext, err := btcec.Encrypt(pubKey, []byte(message))
	if err != nil {
		fmt.Println(err)
		return
	}

	// Decode the hex-encoded private key.
	pkBytes, err := hex.DecodeString("a11b0a4e1a132305652ee7a8eb7848f6ad" +
		"5ea381e3ce20a2c086a2e388230811")
	if err != nil {
		fmt.Println(err)
		return
	}
	// note that we already have corresponding pubKey
	privKey, _ := btcec.PrivKeyFromBytes(btcec.S256(), pkBytes)

	// Try decrypting and verify if it's the same message.
	plaintext, err := btcec.Decrypt(privKey, ciphertext)
	if err != nil {
		fmt.Println(err)
		return
	}

	fmt.Println(string(plaintext))

	// Output:
	// test message
}
func TestPrivKeys(t *testing.T) {
	tests := []struct {
		name string
		key  []byte
	}{
		{
			name: "check curve",
			key: []byte{
				0xea, 0xf0, 0x2c, 0xa3, 0x48, 0xc5, 0x24, 0xe6,
				0x39, 0x26, 0x55, 0xba, 0x4d, 0x29, 0x60, 0x3c,
				0xd1, 0xa7, 0x34, 0x7d, 0x9d, 0x65, 0xcf, 0xe9,
				0x3c, 0xe1, 0xeb, 0xff, 0xdc, 0xa2, 0x26, 0x94,
			},
		},
	}

	for _, test := range tests {
		priv, pub := btcec.PrivKeyFromBytes(btcec.S256(), test.key)

		_, err := btcec.ParsePubKey(
			pub.SerializeUncompressed(), btcec.S256())
		if err != nil {
			t.Errorf("%s privkey: %v", test.name, err)
			continue
		}

		hash := []byte{0x0, 0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8, 0x9}
		sig, err := priv.Sign(hash)
		if err != nil {
			t.Errorf("%s could not sign: %v", test.name, err)
			continue
		}

		if !sig.Verify(hash, pub) {
			t.Errorf("%s could not verify: %v", test.name, err)
			continue
		}

		serializedKey := priv.Serialize()
		if !bytes.Equal(serializedKey, test.key) {
			t.Errorf("%s unexpected serialized bytes - got: %x, "+
				"want: %x", test.name, serializedKey, test.key)
		}
	}
}
// This example demonstrates verifying a secp256k1 signature against a public
// key that is first parsed from raw bytes.  The signature is also parsed from
// raw bytes.
func Example_verifySignature() {
	// Decode hex-encoded serialized public key.
	pubKeyBytes, err := hex.DecodeString("02a673638cb9587cb68ea08dbef685c" +
		"6f2d2a751a8b3c6f2a7e9a4999e6e4bfaf5")
	if err != nil {
		fmt.Println(err)
		return
	}
	pubKey, err := btcec.ParsePubKey(pubKeyBytes, btcec.S256())
	if err != nil {
		fmt.Println(err)
		return
	}

	// Decode hex-encoded serialized signature.
	sigBytes, err := hex.DecodeString("30450220090ebfb3690a0ff115bb1b38b" +
		"8b323a667b7653454f1bccb06d4bbdca42c2079022100ec95778b51e707" +
		"1cb1205f8bde9af6592fc978b0452dafe599481c46d6b2e479")

	if err != nil {
		fmt.Println(err)
		return
	}
	signature, err := btcec.ParseSignature(sigBytes, btcec.S256())
	if err != nil {
		fmt.Println(err)
		return
	}

	// Verify the signature for the message using the public key.
	message := "test message"
	messageHash := wire.DoubleSha256([]byte(message))
	verified := signature.Verify(messageHash, pubKey)
	fmt.Println("Signature Verified?", verified)

	// Output:
	// Signature Verified? true
}
// NewAddressPubKey returns a new AddressPubKey which represents a pay-to-pubkey
// address.  The serializedPubKey parameter must be a valid pubkey and can be
// uncompressed, compressed, or hybrid.
func NewAddressPubKey(serializedPubKey []byte, net *chaincfg.Params) (*AddressPubKey, error) {
	pubKey, err := btcec.ParsePubKey(serializedPubKey, btcec.S256())
	if err != nil {
		return nil, err
	}

	// Set the format of the pubkey.  This probably should be returned
	// from btcec, but do it here to avoid API churn.  We already know the
	// pubkey is valid since it parsed above, so it's safe to simply examine
	// the leading byte to get the format.
	pkFormat := PKFUncompressed
	switch serializedPubKey[0] {
	case 0x02, 0x03:
		pkFormat = PKFCompressed
	case 0x06, 0x07:
		pkFormat = PKFHybrid
	}

	return &AddressPubKey{
		pubKeyFormat: pkFormat,
		pubKey:       pubKey,
		pubKeyHashID: net.PubKeyHashAddrID,
	}, nil
}
// ECPubKey converts the extended key to a btcec public key and returns it.
func (k *ExtendedKey) ECPubKey() (*btcec.PublicKey, error) {
	return btcec.ParsePubKey(k.pubKeyBytes(), btcec.S256())
}
// 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.
//
// 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 possible to
// derive a hardended extended key from a private extended key.  Consequently,
// this function will return ErrDeriveHardFromPublic if a hardened child
// extended key is requested from a public extended key.
//
// A hardened extended key is useful since, as previously mentioned, it requires
// a parent private extended key to derive.  In other words, normal child
// extended public keys can be derived from a parent public extended key (no
// knowledge of the parent private key) whereas hardened extended keys may not
// be.
//
// NOTE: There is an extremely small chance (< 1 in 2^127) the specific child
// index does not derive to a usable child.  The ErrInvalidChild error will be
// returned if this should occur, and the caller is expected to ignore the
// invalid child and simply increment to the next index.
func (k *ExtendedKey) Child(i uint32) (*ExtendedKey, error) {
	// There are four scenarios that could happen here:
	// 1) Private extended key -> Hardened child private extended key
	// 2) Private extended key -> Non-hardened child private extended key
	// 3) Public extended key -> Non-hardened child public extended key
	// 4) Public extended key -> Hardened child public extended key (INVALID!)

	// Case #4 is invalid, so error out early.
	// A hardened child extended key may not be created from a public
	// extended key.
	isChildHardened := i >= HardenedKeyStart
	if !k.isPrivate && isChildHardened {
		return nil, ErrDeriveHardFromPublic
	}

	// The data used to derive the child key depends on whether or not the
	// child is hardened per [BIP32].
	//
	// For hardened children:
	//   0x00 || ser256(parentKey) || ser32(i)
	//
	// For normal children:
	//   serP(parentPubKey) || ser32(i)
	keyLen := 33
	data := make([]byte, keyLen+4)
	if isChildHardened {
		// Case #1.
		// When the child is a hardened child, the key is known to be a
		// private key due to the above early return.  Pad it with a
		// leading zero as required by [BIP32] for deriving the child.
		copy(data[1:], k.key)
	} else {
		// Case #2 or #3.
		// This is either a public or private extended key, but in
		// either case, the data which is used to derive the child key
		// starts with the secp256k1 compressed public key bytes.
		copy(data, k.pubKeyBytes())
	}
	binary.BigEndian.PutUint32(data[keyLen:], i)

	// Take the HMAC-SHA512 of the current key's chain code and the derived
	// data:
	//   I = HMAC-SHA512(Key = chainCode, Data = data)
	hmac512 := hmac.New(sha512.New, k.chainCode)
	hmac512.Write(data)
	ilr := hmac512.Sum(nil)

	// Split "I" into two 32-byte sequences Il and Ir where:
	//   Il = intermediate key used to derive the child
	//   Ir = child chain code
	il := ilr[:len(ilr)/2]
	childChainCode := ilr[len(ilr)/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
	// 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
	// should simply increment to the next index.
	ilNum := new(big.Int).SetBytes(il)
	if ilNum.Cmp(btcec.S256().N) >= 0 || ilNum.Sign() == 0 {
		return nil, ErrInvalidChild
	}

	// The algorithm used to derive the child key depends on whether or not
	// a private or public child is being derived.
	//
	// For private children:
	//   childKey = parse256(Il) + parentKey
	//
	// For public children:
	//   childKey = serP(point(parse256(Il)) + parentKey)
	var isPrivate bool
	var childKey []byte
	if k.isPrivate {
		// Case #1 or #2.
		// Add the parent private key to the intermediate private key to
		// derive the final child key.
		//
		// childKey = parse256(Il) + parenKey
		keyNum := new(big.Int).SetBytes(k.key)
		ilNum.Add(ilNum, keyNum)
		ilNum.Mod(ilNum, btcec.S256().N)
		childKey = ilNum.Bytes()
		isPrivate = true
	} else {
		// Case #3.
		// Calculate the corresponding intermediate public key for
		// intermediate private key.
		ilx, ily := btcec.S256().ScalarBaseMult(il)
		if ilx.Sign() == 0 || ily.Sign() == 0 {
			return nil, ErrInvalidChild
		}

		// Convert the serialized compressed parent public key into X
		// and Y coordinates so it can be added to the intermediate
		// public key.
		pubKey, err := btcec.ParsePubKey(k.key, btcec.S256())
		if err != nil {
			return nil, err
		}

		// Add the intermediate public key to the parent public key to
		// derive the final child key.
		//
		// childKey = serP(point(parse256(Il)) + parentKey)
		childX, childY := btcec.S256().Add(ilx, ily, pubKey.X, pubKey.Y)
		pk := btcec.PublicKey{Curve: btcec.S256(), X: childX, Y: childY}
		childKey = pk.SerializeCompressed()
	}

	// The fingerprint of the parent for the derived child is the first 4
	// bytes of the RIPEMD160(SHA256(parentPubKey)).
	parentFP := btcutil.Hash160(k.pubKeyBytes())[:4]
	return newExtendedKey(k.version, childKey, childChainCode, parentFP,
		k.depth+1, i, isPrivate), nil
}