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Add support for combined descriptor
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As proposed by achow101 on the mailing list, see
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-July/020791.html

Also fix a few compiler warnings.
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@t-bast
t-bast committed Aug 3, 2022
1 parent 1fd1b69 commit 80ed6a5
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Showing 2 changed files with 18 additions and 36 deletions.
46 changes: 15 additions & 31 deletions src/commonMain/kotlin/fr/acinq/bitcoin/Descriptor.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,9 @@ import fr.acinq.bitcoin.DeterministicWallet.derivePrivateKey
import fr.acinq.bitcoin.DeterministicWallet.publicKey
import kotlin.jvm.JvmStatic

/**
* Output Script Descriptors: see https://github.com/bitcoin/bips/blob/master/bip-0380.mediawiki
*/
public object Descriptor {
private fun polyMod(cc: Long, value: Int): Long {
var c = cc
Expand All @@ -17,34 +20,20 @@ public object Descriptor {
return c
}

// Taken from: https://github.com/bitcoin/bitcoin/blob/207a22877330709e4462e6092c265ab55c8653ac/src/script/descriptor.cpp
@JvmStatic
public fun checksum(span: String): String {
/** A character set designed such that:
* - The most common 'unprotected' descriptor characters (hex, keypaths) are in the first group of 32.
* - Case errors cause an offset that's a multiple of 32.
* - As many alphabetic characters are in the same group (while following the above restrictions).
*
* If p(x) gives the position of a character c in this character set, every group of 3 characters
* (a,b,c) is encoded as the 4 symbols (p(a) & 31, p(b) & 31, p(c) & 31, (p(a) / 32) + 3 * (p(b) / 32) + 9 * (p(c) / 32).
* This means that changes that only affect the lower 5 bits of the position, or only the higher 2 bits, will just
* affect a single symbol.
*
* As a result, within-group-of-32 errors count as 1 symbol, as do cross-group errors that don't affect
* the position within the groups.
*/
val INPUT_CHARSET = "0123456789()[],'/*abcdefgh@:$%{}" + "IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~" + "ijklmnopqrstuvwxyzABCDEFGH`#\"\\ "

/** The character set for the checksum itself (same as bech32). */
val CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
val CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"

var c = 1L
var cls = 0
var clscount = 0
span.forEach { ch ->
val pos = INPUT_CHARSET.indexOf(ch);
if (pos == -1) return "";
c = polyMod(c, pos and 31); // Emit a symbol for the position inside the group, for every character.
cls = cls * 3 + (pos shr 5); // Accumulate the group numbers
val pos = INPUT_CHARSET.indexOf(ch)
if (pos == -1) return ""
c = polyMod(c, pos and 31) // Emit a symbol for the position inside the group, for every character.
cls = cls * 3 + (pos shr 5) // Accumulate the group numbers
clscount += 1
if (clscount == 3) {
// Emit an extra symbol representing the group numbers, for every 3 characters.
Expand All @@ -60,8 +49,7 @@ public object Descriptor {
val ret = StringBuilder(" ")
for (j in 0 until 8) {
val pos1 = (c shr (5 * (7 - j))) and 31
val char = CHECKSUM_CHARSET[pos1.toInt()]
ret[j] = char
ret[j] = CHECKSUM_CHARSET[pos1.toInt()]
}
return ret.toString()
}
Expand All @@ -73,21 +61,17 @@ public object Descriptor {
}

@JvmStatic
public fun BIP84Descriptors(chainHash: ByteVector32, master: DeterministicWallet.ExtendedPrivateKey): Pair<String, String> {
public fun BIP84Descriptor(chainHash: ByteVector32, master: DeterministicWallet.ExtendedPrivateKey): String {
val (keyPath, _) = getBIP84KeyPath(chainHash)
val accountPub = publicKey(derivePrivateKey(master, KeyPath(keyPath)))
val fingerprint = DeterministicWallet.fingerprint(master) and 0xFFFFFFFFL
return BIP84Descriptors(chainHash, fingerprint, accountPub)
return BIP84Descriptor(chainHash, fingerprint, accountPub)
}

@JvmStatic
public fun BIP84Descriptors(chainHash: ByteVector32, fingerprint: Long, accountPub: DeterministicWallet.ExtendedPublicKey): Pair<String, String> {
public fun BIP84Descriptor(chainHash: ByteVector32, fingerprint: Long, accountPub: DeterministicWallet.ExtendedPublicKey): String {
val (keyPath, prefix) = getBIP84KeyPath(chainHash)
val accountDesc = "wpkh([${fingerprint.toString(16)}/$keyPath]${DeterministicWallet.encode(accountPub, prefix)}/0/*)"
val changeDesc = "wpkh([${fingerprint.toString(16)}/$keyPath]${DeterministicWallet.encode(accountPub, prefix)}/1/*)"
return Pair(
"$accountDesc#${checksum(accountDesc)}",
"$changeDesc#${checksum(changeDesc)}"
)
val accountDesc = "wpkh([${fingerprint.toString(16)}/$keyPath]${DeterministicWallet.encode(accountPub, prefix)}/<0;1>/*)"
return "$accountDesc#${checksum(accountDesc)}"
}
}
8 changes: 3 additions & 5 deletions src/commonTest/kotlin/fr/acinq/bitcoin/DescriptorTestsCommon.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -19,16 +19,14 @@ class DescriptorTestsCommon {
data.forEach { dnc ->
val (desc, checksum) = dnc.split('#').toTypedArray()
assertEquals(checksum, Descriptor.checksum(desc))
}
}
}

@Test
fun `compute BIP84 descriptors`() {
val seed = ByteVector.fromHex("817a9c8e6ba36f083d7e68b5ee89ce74fde9ef294a724a5efc5cef2b88db057f")
val master = DeterministicWallet.generate(seed)
val (accountDesc, changeDesc) = Descriptor.BIP84Descriptors(Block.RegtestGenesisBlock.hash, master)
assertEquals("wpkh([189ef5fe/84'/1'/0'/0]tpubDFTu6FhLqfTBLMd7BvGkyH1h4XBw7XoKWfnNNWw5Sp8V6aC55EhgPTVNAYvBwBXQ8EGnMqaZi3dpdSzhMbD4Z7ivZiaVKNMUkXVjDU1CDuE/0/*)#uysr3s9y", accountDesc)
assertEquals("wpkh([189ef5fe/84'/1'/0'/0]tpubDFTu6FhLqfTBLMd7BvGkyH1h4XBw7XoKWfnNNWw5Sp8V6aC55EhgPTVNAYvBwBXQ8EGnMqaZi3dpdSzhMbD4Z7ivZiaVKNMUkXVjDU1CDuE/1/*)#ds4zv94u", changeDesc)
val descriptor = Descriptor.BIP84Descriptor(Block.RegtestGenesisBlock.hash, master)
assertEquals("wpkh([189ef5fe/84'/1'/0'/0]tpubDFTu6FhLqfTBLMd7BvGkyH1h4XBw7XoKWfnNNWw5Sp8V6aC55EhgPTVNAYvBwBXQ8EGnMqaZi3dpdSzhMbD4Z7ivZiaVKNMUkXVjDU1CDuE/<0;1>/*)#rw8h72wu", descriptor)
}

}

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