// 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 := chainhash.HashFuncB(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
}
// DecodeWIF creates a new WIF structure by decoding the string encoding of
// the import format.
//
// The WIF string must be a base58-encoded string of the following byte
// sequence:
//
// * 2 bytes to identify the network, must be 0x80 for mainnet or 0xef for
// either testnet or the regression test network
// * 1 extra byte
// * 32 bytes of a binary-encoded, big-endian, zero-padded private key
// * 4 bytes of checksum, must equal the first four bytes of the double SHA256
// of every byte before the checksum in this sequence
//
// If the base58-decoded byte sequence does not match this, DecodeWIF will
// return a non-nil error. ErrMalformedPrivateKey is returned when the WIF
// is of an impossible length. ErrChecksumMismatch is returned if the
// expected WIF checksum does not match the calculated checksum.
func DecodeWIF(wif string) (*WIF, error) {
decoded := base58.Decode(wif)
decodedLen := len(decoded)
if decodedLen != 39 {
return nil, ErrMalformedPrivateKey
}
// Checksum is first four bytes of hash of the identifier byte
// and privKey. Verify this matches the final 4 bytes of the decoded
// private key.
cksum := chainhash.HashFuncB(decoded[:decodedLen-4])
if !bytes.Equal(cksum[:4], decoded[decodedLen-4:]) {
return nil, address.ErrChecksumMismatch
}
netID := [2]byte{decoded[0], decoded[1]}
privKeyBytes := decoded[3 : 3+btcec.PrivKeyBytesLen]
privKey, _ := btcec.PrivKeyFromBytes(curve, privKeyBytes)
return &WIF{0, *privKey, netID}, nil
}
