package keychain import ( "fmt" "github.com/btcsuite/btcd/btcec" ) const ( // KeyDerivationVersion is the version of the key derivation schema // defined below. We use a version as this means that we'll be able to // accept new seed in the future and be able to discern if the software // is compatible with the version of the seed. KeyDerivationVersion = 0 // BIP0043Purpose is the "purpose" value that we'll use for the first // version or our key derivation scheme. All keys are expected to be // derived from this purpose, then the particular coin type of the // chain where the keys are to be used. Slightly adhering to BIP0043 // allows us to not deviate too far from a widely used standard, and // also fits into existing implementations of the BIP's template. // // NOTE: BRICK SQUUUUUAD. BIP0043Purpose = 1017 ) var ( // MaxKeyRangeScan is the maximum number of keys that we'll attempt to // scan with if a caller knows the public key, but not the KeyLocator // and wishes to derive a private key. MaxKeyRangeScan = 100000 // ErrCannotDerivePrivKey is returned when DerivePrivKey is unable to // derive a private key given only the public key and target key // family. ErrCannotDerivePrivKey = fmt.Errorf("unable to derive private key") ) // KeyFamily represents a "family" of keys that will be used within various // contracts created by lnd. These families are meant to be distinct branches // within the HD key chain of the backing wallet. Usage of key families within // the interface below are strict in order to promote integrability and the // ability to restore all keys given a user master seed backup. // // The key derivation in this file follows the following hierarchy based on // BIP43: // // * m/1017'/coinType'/keyFamily/0/index type KeyFamily uint32 const ( // KeyFamilyMultiSig are keys to be used within multi-sig scripts. KeyFamilyMultiSig KeyFamily = 0 // KeyFamilyRevocationBase are keys that are used within channels to // create revocation basepoints that the remote party will use to // create revocation keys for us. KeyFamilyRevocationBase = 1 // KeyFamilyHtlcBase are keys used within channels that will be // combined with per-state randomness to produce public keys that will // be used in HTLC scripts. KeyFamilyHtlcBase KeyFamily = 2 // KeyFamilyPaymentBase are keys used within channels that will be // combined with per-state randomness to produce public keys that will // be used in scripts that pay directly to us without any delay. KeyFamilyPaymentBase KeyFamily = 3 // KeyFamilyDelayBase are keys used within channels that will be // combined with per-state randomness to produce public keys that will // be used in scripts that pay to us, but require a CSV delay before we // can sweep the funds. KeyFamilyDelayBase KeyFamily = 4 // KeyFamilyRevocationRoot is a family of keys which will be used to // derive the root of a revocation tree for a particular channel. KeyFamilyRevocationRoot KeyFamily = 5 // KeyFamilyNodeKey is a family of keys that will be used to derive // keys that will be advertised on the network to represent our current // "identity" within the network. Peers will need our latest node key // in order to establish a transport session with us on the Lightning // p2p level (BOLT-0008). KeyFamilyNodeKey KeyFamily = 6 // KeyFamilyStaticBackup is the family of keys that will be used to // derive keys that we use to encrypt and decrypt our set of static // backups. These backups may either be stored within watch towers for // a payment, or self stored on disk in a single file containing all // the static channel backups. KeyFamilyStaticBackup KeyFamily = 7 ) // KeyLocator is a two-tuple that can be used to derive *any* key that has ever // been used under the key derivation mechanisms described in this file. // Version 0 of our key derivation schema uses the following BIP43-like // derivation: // // * m/201'/coinType'/keyFamily/0/index // // Our purpose is 201 (chosen arbitrary for now), and the coin type will vary // based on which coin/chain the channels are being created on. The key family // are actually just individual "accounts" in the nomenclature of BIP43. By // default we assume a branch of 0 (external). Finally, the key index (which // will vary per channel and use case) is the final element which allows us to // deterministically derive keys. type KeyLocator struct { // TODO(roasbeef): add the key scope as well?? // Family is the family of key being identified. Family KeyFamily // Index is the precise index of the key being identified. Index uint32 } // IsEmpty returns true if a KeyLocator is "empty". This may be the case where // we learn of a key from a remote party for a contract, but don't know the // precise details of its derivation (as we don't know the private key!). func (k KeyLocator) IsEmpty() bool { return k.Family == 0 && k.Index == 0 } // KeyDescriptor wraps a KeyLocator and also optionally includes a public key. // Either the KeyLocator must be non-empty, or the public key pointer be // non-nil. This will be used by the KeyRing interface to lookup arbitrary // private keys, and also within the SignDescriptor struct to locate precisely // which keys should be used for signing. type KeyDescriptor struct { // KeyLocator is the internal KeyLocator of the descriptor. KeyLocator // PubKey is an optional public key that fully describes a target key. // If this is nil, the KeyLocator MUST NOT be empty. PubKey *btcec.PublicKey } // KeyRing is the primary interface that will be used to perform public // derivation of various keys used within the peer-to-peer network, and also // within any created contracts. All derivation required by the KeyRing is // based off of public derivation, so a system with only an extended public key // (for the particular purpose+family) can derive this set of keys. type KeyRing interface { // DeriveNextKey attempts to derive the *next* key within the key // family (account in BIP43) specified. This method should return the // next external child within this branch. DeriveNextKey(keyFam KeyFamily) (KeyDescriptor, error) // DeriveKey attempts to derive an arbitrary key specified by the // passed KeyLocator. This may be used in several recovery scenarios, // or when manually rotating something like our current default node // key. DeriveKey(keyLoc KeyLocator) (KeyDescriptor, error) } // SecretKeyRing is a similar to the regular KeyRing interface, but it is also // able to derive *private keys*. As this is a super-set of the regular // KeyRing, we also expect the SecretKeyRing to implement the fully KeyRing // interface. The methods in this struct may be used to extract the node key in // order to accept inbound network connections, or to do manual signing for // recovery purposes. type SecretKeyRing interface { KeyRing // DerivePrivKey attempts to derive the private key that corresponds to // the passed key descriptor. If the public key is set, then this // method will perform an in-order scan over the key set, with a max of // MaxKeyRangeScan keys. In order for this to work, the caller MUST set // the KeyFamily within the partially populated KeyLocator. DerivePrivKey(keyDesc KeyDescriptor) (*btcec.PrivateKey, error) // ScalarMult performs a scalar multiplication (ECDH-like operation) // between the target key descriptor and remote public key. The output // returned will be the sha256 of the resulting shared point serialized // in compressed format. If k is our private key, and P is the public // key, we perform the following operation: // // sx := k*P // s := sha256(sx.SerializeCompressed()) ScalarMult(keyDesc KeyDescriptor, pubKey *btcec.PublicKey) ([]byte, error) } // TODO(roasbeef): extend to actually support scalar mult of key? // * would allow to push in initial handshake auth into interface as well