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A Kotlin Multiplatform implementation of the Lightning Network
package fr.acinq.lightning.crypto
import fr.acinq.bitcoin.*
import fr.acinq.bitcoin.DeterministicWallet.derivePrivateKey
import fr.acinq.bitcoin.DeterministicWallet.hardened
import fr.acinq.bitcoin.crypto.Pack
import fr.acinq.lightning.Lightning.secureRandom
import fr.acinq.lightning.crypto.LocalKeyManager.Companion.channelKeyPath
/**
* An implementation of [KeyManager] that supports deterministic derivation for [KeyManager.ChannelKeys] based
* on the initial funding pubkey.
*
* Specifically, for channel keys there are two paths:
* - `fundingKeyPath`: chosen at random using [newFundingKeyPath]
* - `channelKeyPath`: computed from `fundingKeyPath` using [channelKeyPath]
*
* The resulting paths looks like so on mainnet:
* ```
* node key:
* 50' / 0'
*
* funding keys:
* 50' / 1' / / <0' or 1'> / '
*
* others channel basepoint keys (payment, revocation, htlc, etc.):
* 50' / 1' / / <1'-5'>
*
* bip-84 on-chain keys:
* 84' / 0' / ' / <0' or 1'> /
* ```
*
* @param seed seed from which the channel keys will be derived
* @param remoteSwapInExtendedPublicKey xpub belonging to our swap-in server, that must be used in our swap address
*/
data class LocalKeyManager(val seed: ByteVector, val chain: Chain, val remoteSwapInExtendedPublicKey: String) : KeyManager {
private val master = DeterministicWallet.generate(seed)
override val nodeKeys: KeyManager.NodeKeys = KeyManager.NodeKeys(
legacyNodeKey = @Suppress("DEPRECATION") derivePrivateKey(master, eclairNodeKeyBasePath(chain)),
nodeKey = derivePrivateKey(master, nodeKeyBasePath(chain)),
)
override val finalOnChainWallet: KeyManager.Bip84OnChainKeys = KeyManager.Bip84OnChainKeys(chain, master, account = 0)
override val swapInOnChainWallet: KeyManager.SwapInOnChainKeys = run {
val (prefix, xpub) = DeterministicWallet.ExtendedPublicKey.decode(remoteSwapInExtendedPublicKey)
val expectedPrefix = when (chain) {
Chain.Mainnet -> DeterministicWallet.xpub
else -> DeterministicWallet.tpub
}
require(prefix == expectedPrefix) { "unexpected swap-in xpub prefix $prefix (expected $expectedPrefix)" }
val remoteSwapInPublicKey = DeterministicWallet.derivePublicKey(xpub, KeyManager.SwapInOnChainKeys.perUserPath(nodeKeys.nodeKey.publicKey)).publicKey
KeyManager.SwapInOnChainKeys(chain, master, remoteSwapInPublicKey)
}
private val channelKeyBasePath: KeyPath = channelKeyBasePath(chain)
/**
* This method offers direct access to the master key derivation. It should only be used for some advanced usage
* like (LNURL-auth, data encryption).
*/
fun derivePrivateKey(keyPath: KeyPath): DeterministicWallet.ExtendedPrivateKey = derivePrivateKey(master, keyPath)
fun privateKey(keyPath: KeyPath): PrivateKey = derivePrivateKey(master, keyPath).privateKey
override fun newFundingKeyPath(isInitiator: Boolean): KeyPath {
val last = hardened(if (isInitiator) 1 else 0)
fun next() = secureRandom.nextInt().toLong() and 0xFFFFFFFF
return KeyPath.empty / next() / next() / next() / next() / next() / next() / next() / next() / last
}
override fun channelKeys(fundingKeyPath: KeyPath): KeyManager.ChannelKeys {
// We use a different funding key for each splice, with a derivation based on the fundingTxIndex.
val fundingKey: (Long) -> PrivateKey = { index -> derivePrivateKey(master, channelKeyBasePath / fundingKeyPath / hardened(index)).privateKey }
// We use the initial funding pubkey to compute the channel key path, and we use the recovery process even
// in the normal case, which guarantees it works all the time.
val initialFundingPubkey = fundingKey(0).publicKey()
val recoveredChannelKeys = recoverChannelKeys(initialFundingPubkey)
return KeyManager.ChannelKeys(
fundingKeyPath,
fundingKey = fundingKey,
paymentKey = recoveredChannelKeys.paymentKey,
delayedPaymentKey = recoveredChannelKeys.delayedPaymentKey,
htlcKey = recoveredChannelKeys.htlcKey,
revocationKey = recoveredChannelKeys.revocationKey,
shaSeed = recoveredChannelKeys.shaSeed
)
}
/**
* Generate channel-specific keys and secrets (note that we cannot re-compute the channel's funding private key)
* @params fundingPubKey funding public key
* @return channel keys and secrets
*/
fun recoverChannelKeys(fundingPubKey: PublicKey): RecoveredChannelKeys {
val channelKeyPrefix = channelKeyBasePath / channelKeyPath(fundingPubKey)
return RecoveredChannelKeys(
fundingPubKey,
paymentKey = privateKey(channelKeyPrefix / hardened(2)),
delayedPaymentKey = privateKey(channelKeyPrefix / hardened(3)),
htlcKey = privateKey(channelKeyPrefix / hardened(4)),
revocationKey = privateKey(channelKeyPrefix / hardened(1)),
shaSeed = privateKey(channelKeyPrefix / hardened(5)).value.concat(1).sha256()
)
}
/**
* Channel keys recovered from the channel's funding public key (note that we cannot recover the funding private key).
* These keys can be used to spend our outputs from a commit tx that has been published to the blockchain, without any other information than
* the node's seed ("backup less backup")
*/
data class RecoveredChannelKeys(
val fundingPubKey: PublicKey,
val paymentKey: PrivateKey,
val delayedPaymentKey: PrivateKey,
val htlcKey: PrivateKey,
val revocationKey: PrivateKey,
val shaSeed: ByteVector32
) {
val htlcBasepoint: PublicKey = htlcKey.publicKey()
val paymentBasepoint: PublicKey = paymentKey.publicKey()
val delayedPaymentBasepoint: PublicKey = delayedPaymentKey.publicKey()
val revocationBasepoint: PublicKey = revocationKey.publicKey()
}
override fun toString(): String = "LocalKeyManager(seed=,chain=$chain)"
/**
* WARNING: If you change the paths below, keys will change (including your node id) even if the seed remains the same!!!
* Note that the node path and the above channel path are on different branches so even if the
* node key is compromised there is no way to retrieve the wallet keys
*/
companion object {
/**
* Create a BIP32 path from a public key. This path will be used to derive channel keys.
* Having channel keys derived from the funding public keys makes it very easy to retrieve your funds when you've lost your data:
* - connect to your peer and use DLP to get them to publish their remote commit tx
* - retrieve the commit tx from the bitcoin network, extract your funding pubkey from its witness data
* - recompute your channel keys and spend your output
*
* @param fundingPubKey funding public key
* @return a BIP32 path
*/
fun channelKeyPath(fundingPubKey: PublicKey): KeyPath {
val buffer = fundingPubKey.value.sha256().toByteArray()
val path = (0 until 8).map { i -> Pack.int32BE(buffer, 4 * i).toUInt().toLong() }
return KeyPath(path)
}
fun channelKeyBasePath(chain: Chain) = when (chain) {
Chain.Regtest, Chain.Testnet, Chain.Signet -> KeyPath.empty / hardened(48) / hardened(1)
Chain.Mainnet -> KeyPath.empty / hardened(50) / hardened(1)
}
/** Path for node keys generated by eclair-core */
@Deprecated("used for backward-compat with eclair-core", replaceWith = ReplaceWith("nodeKeyBasePath(chain)"))
fun eclairNodeKeyBasePath(chain: Chain) = when (chain) {
Chain.Regtest, Chain.Testnet, Chain.Signet -> KeyPath.empty / hardened(46) / hardened(0)
Chain.Mainnet -> KeyPath.empty / hardened(47) / hardened(0)
}
fun nodeKeyBasePath(chain: Chain) = when (chain) {
Chain.Regtest, Chain.Testnet, Chain.Signet -> KeyPath.empty / hardened(48) / hardened(0)
Chain.Mainnet -> KeyPath.empty / hardened(50) / hardened(0)
}
}
}
infix operator fun KeyPath.div(index: Long): KeyPath = this.append(index)
infix operator fun KeyPath.div(other: KeyPath): KeyPath = this.append(other)
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