From 7cedafc5412857404e9a6c3450b100cb8ee4081a Mon Sep 17 00:00:00 2001 From: Pieter Wuille Date: Sun, 7 Feb 2021 19:18:39 -0800 Subject: [PATCH] Add tr() descriptor (derivation only, no signing) This adds a new descriptor with syntax e.g. tr(KEY,{S1,{{S2,S3},S4}) where KEY is a key expression for the internal key and S_i are script expression for the leaves. They have to be organized in nested {A,B} groups, with exactly two elements. tr() only exists at the top level, and inside the script expressions only pk() scripts are allowed for now. --- doc/descriptors.md | 18 +++-- src/pubkey.h | 3 + src/script/descriptor.cpp | 151 ++++++++++++++++++++++++++++++++++++-- src/util/spanparsing.cpp | 6 +- 4 files changed, 163 insertions(+), 15 deletions(-) diff --git a/doc/descriptors.md b/doc/descriptors.md index c4fc2a66bf2..e27ff875468 100644 --- a/doc/descriptors.md +++ b/doc/descriptors.md @@ -30,6 +30,7 @@ Output descriptors currently support: - Pay-to-witness-pubkey-hash scripts (P2WPKH), through the `wpkh` function. - Pay-to-script-hash scripts (P2SH), through the `sh` function. - Pay-to-witness-script-hash scripts (P2WSH), through the `wsh` function. +- Pay-to-taproot outputs (P2TR), through the `tr` function. - Multisig scripts, through the `multi` function. - Multisig scripts where the public keys are sorted lexicographically, through the `sortedmulti` function. - Any type of supported address through the `addr` function. @@ -54,6 +55,7 @@ Output descriptors currently support: - `pkh([d34db33f/44'/0'/0']xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/*)` describes a set of P2PKH outputs, but additionally specifies that the specified xpub is a child of a master with fingerprint `d34db33f`, and derived using path `44'/0'/0'`. - `wsh(multi(1,xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB/1/0/*,xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH/0/0/*))` describes a set of *1-of-2* P2WSH multisig outputs where the first multisig key is the *1/0/`i`* child of the first specified xpub and the second multisig key is the *0/0/`i`* child of the second specified xpub, and `i` is any number in a configurable range (`0-1000` by default). - `wsh(sortedmulti(1,xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB/1/0/*,xpub69H7F5d8KSRgmmdJg2KhpAK8SR3DjMwAdkxj3ZuxV27CprR9LgpeyGmXUbC6wb7ERfvrnKZjXoUmmDznezpbZb7ap6r1D3tgFxHmwMkQTPH/0/0/*))` describes a set of *1-of-2* P2WSH multisig outputs where one multisig key is the *1/0/`i`* child of the first specified xpub and the other multisig key is the *0/0/`i`* child of the second specified xpub, and `i` is any number in a configurable range (`0-1000` by default). The order of public keys in the resulting witnessScripts is determined by the lexicographic order of the public keys at that index. +- `tr(c6047f9441ed7d6d3045406e95c07cd85c778e4b8cef3ca7abac09b95c709ee5,{pk(fff97bd5755eeea420453a14355235d382f6472f8568a18b2f057a1460297556),pk(e493dbf1c10d80f3581e4904930b1404cc6c13900ee0758474fa94abe8c4cd13)})` describes a P2TR output with the `c6...` x-only pubkey as internal key, and two script paths. ## Reference @@ -61,13 +63,14 @@ Descriptors consist of several types of expressions. The top level expression is `SCRIPT` expressions: - `sh(SCRIPT)` (top level only): P2SH embed the argument. -- `wsh(SCRIPT)` (not inside another 'wsh'): P2WSH embed the argument. +- `wsh(SCRIPT)` (top level or inside `sh` only): P2WSH embed the argument. - `pk(KEY)` (anywhere): P2PK output for the given public key. -- `pkh(KEY)` (anywhere): P2PKH output for the given public key (use `addr` if you only know the pubkey hash). -- `wpkh(KEY)` (not inside `wsh`): P2WPKH output for the given compressed pubkey. +- `pkh(KEY)` (not inside `tr`): P2PKH output for the given public key (use `addr` if you only know the pubkey hash). +- `wpkh(KEY)` (top level or inside `sh` only): P2WPKH output for the given compressed pubkey. - `combo(KEY)` (top level only): an alias for the collection of `pk(KEY)` and `pkh(KEY)`. If the key is compressed, it also includes `wpkh(KEY)` and `sh(wpkh(KEY))`. -- `multi(k,KEY_1,KEY_2,...,KEY_n)` (anywhere): k-of-n multisig script. -- `sortedmulti(k,KEY_1,KEY_2,...,KEY_n)` (anywhere): k-of-n multisig script with keys sorted lexicographically in the resulting script. +- `multi(k,KEY_1,KEY_2,...,KEY_n)` (not inside `tr`): k-of-n multisig script. +- `sortedmulti(k,KEY_1,KEY_2,...,KEY_n)` (not inside `tr`): k-of-n multisig script with keys sorted lexicographically in the resulting script. +- `tr(KEY)` or `tr(KEY,TREE)` (top level only): P2TR output with the specified key as internal key, and optionally a tree of script paths. - `addr(ADDR)` (top level only): the script which ADDR expands to. - `raw(HEX)` (top level only): the script whose hex encoding is HEX. @@ -80,12 +83,17 @@ Descriptors consist of several types of expressions. The top level expression is - Followed by the actual key, which is either: - Hex encoded public keys (either 66 characters starting with `02` or `03` for a compressed pubkey, or 130 characters starting with `04` for an uncompressed pubkey). - Inside `wpkh` and `wsh`, only compressed public keys are permitted. + - Inside `tr`, x-only pubkeys are also permitted (64 hex characters). - [WIF](https://en.bitcoin.it/wiki/Wallet_import_format) encoded private keys may be specified instead of the corresponding public key, with the same meaning. - `xpub` encoded extended public key or `xprv` encoded extended private key (as defined in [BIP 32](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki)). - Followed by zero or more `/NUM` unhardened and `/NUM'` hardened BIP32 derivation steps. - Optionally followed by a single `/*` or `/*'` final step to denote all (direct) unhardened or hardened children. - The usage of hardened derivation steps requires providing the private key. +`TREE` expressions: +- any `SCRIPT` expression +- An open brace `{`, a `TREE` expression, a comma `,`, a `TREE` expression, and a closing brace `}` + (Anywhere a `'` suffix is permitted to denote hardened derivation, the suffix `h` can be used instead.) `ADDR` expressions are any type of supported address: diff --git a/src/pubkey.h b/src/pubkey.h index 4de1807a7f5..152a48dd180 100644 --- a/src/pubkey.h +++ b/src/pubkey.h @@ -237,6 +237,9 @@ public: /** Construct an x-only pubkey from exactly 32 bytes. */ explicit XOnlyPubKey(Span bytes); + /** Construct an x-only pubkey from a normal pubkey. */ + explicit XOnlyPubKey(const CPubKey& pubkey) : XOnlyPubKey(Span(pubkey.begin() + 1, pubkey.begin() + 33)) {} + /** Verify a Schnorr signature against this public key. * * sigbytes must be exactly 64 bytes. diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp index d4b43932b91..51cf8a7d623 100644 --- a/src/script/descriptor.cpp +++ b/src/script/descriptor.cpp @@ -241,9 +241,10 @@ public: class ConstPubkeyProvider final : public PubkeyProvider { CPubKey m_pubkey; + bool m_xonly; public: - ConstPubkeyProvider(uint32_t exp_index, const CPubKey& pubkey) : PubkeyProvider(exp_index), m_pubkey(pubkey) {} + ConstPubkeyProvider(uint32_t exp_index, const CPubKey& pubkey, bool xonly = false) : PubkeyProvider(exp_index), m_pubkey(pubkey), m_xonly(xonly) {} bool GetPubKey(int pos, const SigningProvider& arg, CPubKey& key, KeyOriginInfo& info, const DescriptorCache* read_cache = nullptr, DescriptorCache* write_cache = nullptr) override { key = m_pubkey; @@ -254,7 +255,7 @@ public: } bool IsRange() const override { return false; } size_t GetSize() const override { return m_pubkey.size(); } - std::string ToString() const override { return HexStr(m_pubkey); } + std::string ToString() const override { return m_xonly ? HexStr(m_pubkey).substr(2) : HexStr(m_pubkey); } bool ToPrivateString(const SigningProvider& arg, std::string& ret) const override { CKey key; @@ -505,6 +506,7 @@ protected: public: DescriptorImpl(std::vector> pubkeys, const std::string& name) : m_pubkey_args(std::move(pubkeys)), m_name(name), m_subdescriptor_args() {} DescriptorImpl(std::vector> pubkeys, std::unique_ptr script, const std::string& name) : m_pubkey_args(std::move(pubkeys)), m_name(name), m_subdescriptor_args(Vector(std::move(script))) {} + DescriptorImpl(std::vector> pubkeys, std::vector> scripts, const std::string& name) : m_pubkey_args(std::move(pubkeys)), m_name(name), m_subdescriptor_args(std::move(scripts)) {} bool IsSolvable() const override { @@ -693,10 +695,20 @@ public: /** A parsed pk(P) descriptor. */ class PKDescriptor final : public DescriptorImpl { +private: + const bool m_xonly; protected: - std::vector MakeScripts(const std::vector& keys, Span, FlatSigningProvider&) const override { return Vector(GetScriptForRawPubKey(keys[0])); } + std::vector MakeScripts(const std::vector& keys, Span, FlatSigningProvider&) const override + { + if (m_xonly) { + CScript script = CScript() << ToByteVector(XOnlyPubKey(keys[0])) << OP_CHECKSIG; + return Vector(std::move(script)); + } else { + return Vector(GetScriptForRawPubKey(keys[0])); + } + } public: - PKDescriptor(std::unique_ptr prov) : DescriptorImpl(Vector(std::move(prov)), "pk") {} + PKDescriptor(std::unique_ptr prov, bool xonly = false) : DescriptorImpl(Vector(std::move(prov)), "pk"), m_xonly(xonly) {} bool IsSingleType() const final { return true; } }; @@ -814,6 +826,56 @@ public: bool IsSingleType() const final { return true; } }; +/** A parsed tr(...) descriptor. */ +class TRDescriptor final : public DescriptorImpl +{ + std::vector m_depths; +protected: + std::vector MakeScripts(const std::vector& keys, Span scripts, FlatSigningProvider& out) const override + { + TaprootBuilder builder; + assert(m_depths.size() == scripts.size()); + for (size_t pos = 0; pos < m_depths.size(); ++pos) { + builder.Add(m_depths[pos], scripts[pos], TAPROOT_LEAF_TAPSCRIPT); + } + if (!builder.IsComplete()) return {}; + assert(keys.size() == 1); + XOnlyPubKey xpk(keys[0]); + if (!xpk.IsFullyValid()) return {}; + builder.Finalize(xpk); + return Vector(GetScriptForDestination(builder.GetOutput())); + } + bool ToStringSubScriptHelper(const SigningProvider* arg, std::string& ret, bool priv, bool normalized) const override + { + if (m_depths.empty()) return true; + std::vector path; + for (size_t pos = 0; pos < m_depths.size(); ++pos) { + if (pos) ret += ','; + while ((int)path.size() <= m_depths[pos]) { + if (path.size()) ret += '{'; + path.push_back(false); + } + std::string tmp; + if (!m_subdescriptor_args[pos]->ToStringHelper(arg, tmp, priv, normalized)) return false; + ret += std::move(tmp); + while (!path.empty() && path.back()) { + if (path.size() > 1) ret += '}'; + path.pop_back(); + } + if (!path.empty()) path.back() = true; + } + return true; + } +public: + TRDescriptor(std::unique_ptr internal_key, std::vector> descs, std::vector depths) : + DescriptorImpl(Vector(std::move(internal_key)), std::move(descs), "tr"), m_depths(std::move(depths)) + { + assert(m_subdescriptor_args.size() == m_depths.size()); + } + std::optional GetOutputType() const override { return OutputType::BECH32; } + bool IsSingleType() const final { return true; } +}; + //////////////////////////////////////////////////////////////////////////// // Parser // //////////////////////////////////////////////////////////////////////////// @@ -823,6 +885,7 @@ enum class ParseScriptContext { P2SH, //!< Inside sh() (script becomes P2SH redeemScript) P2WPKH, //!< Inside wpkh() (no script, pubkey only) P2WSH, //!< Inside wsh() (script becomes v0 witness script) + P2TR, //!< Inside tr() (either internal key, or BIP342 script leaf) }; /** Parse a key path, being passed a split list of elements (the first element is ignored). */ @@ -871,6 +934,13 @@ std::unique_ptr ParsePubkeyInner(uint32_t key_exp_index, const S error = "Uncompressed keys are not allowed"; return nullptr; } + } else if (data.size() == 32 && ctx == ParseScriptContext::P2TR) { + unsigned char fullkey[33] = {0x02}; + std::copy(data.begin(), data.end(), fullkey + 1); + pubkey.Set(std::begin(fullkey), std::end(fullkey)); + if (pubkey.IsFullyValid()) { + return std::make_unique(key_exp_index, pubkey, true); + } } error = strprintf("Pubkey '%s' is invalid", str); return nullptr; @@ -958,13 +1028,16 @@ std::unique_ptr ParseScript(uint32_t& key_exp_index, Span(std::move(pubkey)); + return std::make_unique(std::move(pubkey), ctx == ParseScriptContext::P2TR); } - if (Func("pkh", expr)) { + if ((ctx == ParseScriptContext::TOP || ctx == ParseScriptContext::P2SH || ctx == ParseScriptContext::P2WSH) && Func("pkh", expr)) { auto pubkey = ParsePubkey(key_exp_index, expr, ctx, out, error); if (!pubkey) return nullptr; ++key_exp_index; return std::make_unique(std::move(pubkey)); + } else if (Func("pkh", expr)) { + error = "Can only have pkh at top level, in sh(), or in wsh()"; + return nullptr; } if (ctx == ParseScriptContext::TOP && Func("combo", expr)) { auto pubkey = ParsePubkey(key_exp_index, expr, ctx, out, error); @@ -975,7 +1048,7 @@ std::unique_ptr ParseScript(uint32_t& key_exp_index, Span> providers; @@ -1020,6 +1093,9 @@ std::unique_ptr ParseScript(uint32_t& key_exp_index, Span(thres, std::move(providers), sorted_multi); + } else if (Func("sortedmulti", expr) || Func("multi", expr)) { + error = "Can only have multi/sortedmulti at top level, in sh(), or in wsh()"; + return nullptr; } if ((ctx == ParseScriptContext::TOP || ctx == ParseScriptContext::P2SH) && Func("wpkh", expr)) { auto pubkey = ParsePubkey(key_exp_index, expr, ParseScriptContext::P2WPKH, out, error); @@ -1057,6 +1133,67 @@ std::unique_ptr ParseScript(uint32_t& key_exp_index, Span> subscripts; //!< list of script subexpressions + std::vector depths; //!< depth in the tree of each subexpression (same length subscripts) + if (expr.size()) { + if (!Const(",", expr)) { + error = strprintf("tr: expected ',', got '%c'", expr[0]); + return nullptr; + } + /** The path from the top of the tree to what we're currently processing. + * branches[i] == false: left branch in the i'th step from the top; true: right branch. + */ + std::vector branches; + // Loop over all provided scripts. In every iteration exactly one script will be processed. + // Use a do-loop because inside this if-branch we expect at least one script. + do { + // First process all open braces. + while (Const("{", expr)) { + branches.push_back(false); // new left branch + if (branches.size() > TAPROOT_CONTROL_MAX_NODE_COUNT) { + error = strprintf("tr() supports at most %i nesting levels", TAPROOT_CONTROL_MAX_NODE_COUNT); + return nullptr; + } + } + // Process the actual script expression. + auto sarg = Expr(expr); + subscripts.emplace_back(ParseScript(key_exp_index, sarg, ParseScriptContext::P2TR, out, error)); + if (!subscripts.back()) return nullptr; + depths.push_back(branches.size()); + // Process closing braces; one is expected for every right branch we were in. + while (branches.size() && branches.back()) { + if (!Const("}", expr)) { + error = strprintf("tr(): expected '}' after script expression"); + return nullptr; + } + branches.pop_back(); // move up one level after encountering '}' + } + // If after that, we're at the end of a left branch, expect a comma. + if (branches.size() && !branches.back()) { + if (!Const(",", expr)) { + error = strprintf("tr(): expected ',' after script expression"); + return nullptr; + } + branches.back() = true; // And now we're in a right branch. + } + } while (branches.size()); + // After we've explored a whole tree, we must be at the end of the expression. + if (expr.size()) { + error = strprintf("tr(): expected ')' after script expression"); + return nullptr; + } + } + assert(TaprootBuilder::ValidDepths(depths)); + return std::make_unique(std::move(internal_key), std::move(subscripts), std::move(depths)); + } else if (Func("tr", expr)) { + error = "Can only have tr at top level"; + return nullptr; + } if (ctx == ParseScriptContext::TOP && Func("raw", expr)) { std::string str(expr.begin(), expr.end()); if (!IsHex(str)) { diff --git a/src/util/spanparsing.cpp b/src/util/spanparsing.cpp index 0f68254f2c2..e2e2782bec2 100644 --- a/src/util/spanparsing.cpp +++ b/src/util/spanparsing.cpp @@ -34,11 +34,11 @@ Span Expr(Span& sp) int level = 0; auto it = sp.begin(); while (it != sp.end()) { - if (*it == '(') { + if (*it == '(' || *it == '{') { ++level; - } else if (level && *it == ')') { + } else if (level && (*it == ')' || *it == '}')) { --level; - } else if (level == 0 && (*it == ')' || *it == ',')) { + } else if (level == 0 && (*it == ')' || *it == '}' || *it == ',')) { break; } ++it;