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extendedkey.go
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extendedkey.go
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package hdkey
import (
"errors"
"fmt"
"golang.org/x/crypto/ed25519"
)
const (
// RecommendedSeedLen is the recommended length in bytes for a seed
// to a master node.
RecommendedSeedLen = 32 // 256 bits
// HardenedKeyStart is the index at which a hardened key starts. Each
// extended key has 2^31 normal child keys and 2^31 hardened child keys.
// Thus the range for normal child keys is [0, 2^31 - 1] and the range
// for hardened child keys is [2^31, 2^32 - 1].
HardenedKeyStart = 0x80000000 // 2^31
// MinSeedBytes is the minimum number of bytes allowed for a seed to
// a master node.
MinSeedBytes = 16 // 128 bits
// MaxSeedBytes is the maximum number of bytes allowed for a seed to
// a master node.
MaxSeedBytes = 64 // 512 bits
// serializedKeyLen is the length of a serialized public or private
// extended key. It consists of 4 bytes version, 1 byte depth, 4 bytes
// fingerprint, 4 bytes child number, 32 bytes chain code, and 33 bytes
// public/private key data.
serializedKeyLen = 4 + 1 + 4 + 4 + 32 + 33 //nolint:unused // 78 bytes
// maxUint8 is the max positive integer which can be serialized in a uint8
maxUint8 = 1<<8 - 1
)
var (
// ErrDeriveHardFromPublic describes an error in which the caller
// attempted to derive a hardened extended key from a public key.
ErrDeriveHardFromPublic = errors.New("cannot derive a hardened key " +
"from a public key")
// ErrDeriveBeyondMaxDepth describes an error in which the caller
// has attempted to derive more than 255 keys from a root key.
ErrDeriveBeyondMaxDepth = errors.New("cannot derive a key with more than " +
"255 indices in its path")
// ErrNotPrivExtKey describes an error in which the caller attempted
// to extract a private key from a public extended key.
ErrNotPrivExtKey = errors.New("unable to create private keys from a " +
"public extended key")
// ErrInvalidChild describes an error in which the child at a specific
// index is invalid due to the derived key falling outside of the valid
// range for secp256k1 private keys. This error indicates the caller
// should simply ignore the invalid child extended key at this index and
// increment to the next index.
ErrInvalidChild = errors.New("the extended key at this index is invalid")
// ErrUnusableSeed describes an error in which the provided seed is not
// usable due to the derived key falling outside of the valid range for
// secp256k1 private keys. This error indicates the caller must choose
// another seed.
ErrUnusableSeed = errors.New("unusable seed")
// ErrInvalidSeedLen describes an error in which the provided seed or
// seed length is not in the allowed range.
ErrInvalidSeedLen = fmt.Errorf("seed length must be between %d and %d "+
"bits", MinSeedBytes*8, MaxSeedBytes*8)
// ErrBadChecksum describes an error in which the checksum encoded with
// a serialized extended key does not match the calculated value.
ErrBadChecksum = errors.New("bad extended key checksum")
// ErrInvalidKeyLen describes an error in which the provided serialized
// key is not the expected length.
ErrInvalidKeyLen = errors.New("the provided serialized extended key " +
"length is invalid")
)
// ExtendedKey houses all the information needed to support a hierarchical
// deterministic extended key. See the package overview documentation for
// more details on how to use extended keys.
type ExtendedKey struct {
key []byte // This will be the pubkey for extended pub keys
pubKey []byte // This will only be set for extended priv keys
chainCode []byte
depth uint8
parentFP []byte
childNum uint32
isPrivate bool
}
// NewExtendedKey returns a new instance of an extended key with the given
// fields. No error checking is performed here as it's only intended to be a
// convenience method used to create a populated struct. This function should
// only by used by applications that need to create custom ExtendedKeys. All
// other applications should just use NewMaster, Child, or Neuter.
func NewExtendedKey(key, chainCode, parentFP []byte, depth uint8,
childNum uint32, isPrivate bool) *ExtendedKey {
// NOTE: The pubKey field is intentionally left nil so it is only
// computed and memoized as required.
return &ExtendedKey{
key: key,
chainCode: chainCode,
depth: depth,
parentFP: parentFP,
childNum: childNum,
isPrivate: isPrivate,
}
}
func (e ExtendedKey) Depth() uint8 {
return e.depth
}
func (e ExtendedKey) PublicKey() []byte {
if e.isPrivate {
fullKey := ed25519.NewKeyFromSeed(e.key)
return fullKey.Public().(ed25519.PublicKey)
} else {
return e.pubKey
}
}
func (e ExtendedKey) PrivateKey() []byte {
return e.key
}