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miniscript: add a scaffold of parsing wsh(<miniscript>) policies
We add a policies.rs file with functions to parse and validate a policy containing miniscript. Policy specification: bitcoin/bips#1389 We only support `wsh(<miniscript>)` policies for now. Taproot or other policy fragments could be added in the future. More validation checks are coming in later commits, such as: - At least one key must be ours - No duplicate keys possible in the policy - No duplicate keys in the keys list - All keys in the keys list are used, and all key references (@0, ...) are valid. - ...? Also coming in later commits: - Derive a pkScript at a keypath, generate receive address from that - Policy registration (very similar to how multisig registration works today) - Signing transactions
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// Copyright 2023 Shift Crypto AG | ||
// | ||
// Licensed under the Apache License, Version 2.0 (the "License"); | ||
// you may not use this file except in compliance with the License. | ||
// You may obtain a copy of the License at | ||
// | ||
// http://www.apache.org/licenses/LICENSE-2.0 | ||
// | ||
// Unless required by applicable law or agreed to in writing, software | ||
// distributed under the License is distributed on an "AS IS" BASIS, | ||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
// See the License for the specific language governing permissions and | ||
// limitations under the License. | ||
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use super::pb; | ||
use super::Error; | ||
use pb::BtcCoin; | ||
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use pb::btc_script_config::Policy; | ||
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use alloc::string::String; | ||
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use core::str::FromStr; | ||
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// Arbitrary limit of keys that can be present in a policy. | ||
const MAX_KEYS: usize = 20; | ||
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// We only support Bitcoin testnet for now. | ||
fn check_enabled(coin: BtcCoin) -> Result<(), Error> { | ||
if !matches!(coin, BtcCoin::Tbtc) { | ||
return Err(Error::InvalidInput); | ||
} | ||
Ok(()) | ||
} | ||
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/// See `ParsedPolicy`. | ||
#[derive(Debug)] | ||
pub struct Wsh<'a> { | ||
policy: &'a Policy, | ||
miniscript_expr: miniscript::Miniscript<String, miniscript::Segwitv0>, | ||
} | ||
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/// Result of `parse()`. | ||
#[derive(Debug)] | ||
pub enum ParsedPolicy<'a> { | ||
// `wsh(...)` policies | ||
Wsh(Wsh<'a>), | ||
// `tr(...)` Taproot etc. in the future. | ||
} | ||
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impl<'a> ParsedPolicy<'a> { | ||
fn get_policy(&self) -> &Policy { | ||
match self { | ||
Self::Wsh(Wsh { ref policy, .. }) => policy, | ||
} | ||
} | ||
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/// Validate a policy. | ||
/// - Coin is supported (only Bitcoin testnet for now) | ||
/// - Number of keys | ||
/// - TODO: many more checks. | ||
pub fn validate(&self, coin: BtcCoin) -> Result<(), Error> { | ||
check_enabled(coin)?; | ||
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let policy = self.get_policy(); | ||
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if policy.keys.len() > MAX_KEYS { | ||
return Err(Error::InvalidInput); | ||
} | ||
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// TODO: more checks | ||
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Ok(()) | ||
} | ||
} | ||
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/// Parses a policy as specified by 'Wallet policies': https://github.com/bitcoin/bips/pull/1389. | ||
/// Only `wsh(<miniscript expression>)` is supported for now. | ||
/// Example: `wsh(pk(@0/**))`. | ||
pub fn parse(policy: &Policy) -> Result<ParsedPolicy, Error> { | ||
let desc = policy.policy.as_str(); | ||
match desc.as_bytes() { | ||
// Match wsh(...). | ||
[b'w', b's', b'h', b'(', .., b')'] => { | ||
let miniscript_expr: miniscript::Miniscript<String, miniscript::Segwitv0> = | ||
miniscript::Miniscript::from_str(&desc[4..desc.len() - 1]) | ||
.or(Err(Error::InvalidInput))?; | ||
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Ok(ParsedPolicy::Wsh(Wsh { | ||
policy, | ||
miniscript_expr, | ||
})) | ||
} | ||
_ => Err(Error::InvalidInput), | ||
} | ||
} | ||
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#[cfg(test)] | ||
mod tests { | ||
use super::*; | ||
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use alloc::vec::Vec; | ||
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use crate::bip32::parse_xpub; | ||
use bitbox02::testing::mock_unlocked; | ||
use util::bip32::HARDENED; | ||
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const SOME_XPUB_1: &str = "xpub6FMWuwbCA9KhoRzAMm63ZhLspk5S2DM5sePo8J8mQhcS1xyMbAqnc7Q7UescVEVFCS6qBMQLkEJWQ9Z3aDPgBov5nFUYxsJhwumsxM4npSo"; | ||
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const KEYPATH_ACCOUNT: &[u32] = &[48 + HARDENED, 1 + HARDENED, 0 + HARDENED, 3 + HARDENED]; | ||
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// Creates a policy key without fingerprint/keypath from an xpub string. | ||
fn make_key(xpub: &str) -> pb::KeyOriginInfo { | ||
pb::KeyOriginInfo { | ||
root_fingerprint: vec![], | ||
keypath: vec![], | ||
xpub: Some(parse_xpub(xpub).unwrap()), | ||
} | ||
} | ||
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// Creates a policy for one of our own keys at keypath. | ||
fn make_our_key(keypath: &[u32]) -> pb::KeyOriginInfo { | ||
let our_xpub = crate::keystore::get_xpub(keypath).unwrap(); | ||
pb::KeyOriginInfo { | ||
root_fingerprint: crate::keystore::root_fingerprint().unwrap(), | ||
keypath: keypath.to_vec(), | ||
xpub: Some(our_xpub.into()), | ||
} | ||
} | ||
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fn make_policy(policy: &str, keys: &[pb::KeyOriginInfo]) -> Policy { | ||
Policy { | ||
policy: policy.into(), | ||
keys: keys.to_vec(), | ||
} | ||
} | ||
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#[test] | ||
fn test_parse_wsh_miniscript() { | ||
// Parse a valid example and check that the keys are collected as is as strings. | ||
let policy = make_policy("wsh(pk(@0/**))", &[]); | ||
match parse(&policy).unwrap() { | ||
ParsedPolicy::Wsh(Wsh { | ||
ref miniscript_expr, | ||
.. | ||
}) => { | ||
assert_eq!( | ||
miniscript_expr.iter_pk().collect::<Vec<String>>(), | ||
vec!["@0/**"] | ||
); | ||
} | ||
} | ||
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// Parse another valid example and check that the keys are collected as is as strings. | ||
let policy = make_policy("wsh(or_b(pk(@0/**),s:pk(@1/**)))", &[]); | ||
match parse(&policy).unwrap() { | ||
ParsedPolicy::Wsh(Wsh { | ||
ref miniscript_expr, | ||
.. | ||
}) => { | ||
assert_eq!( | ||
miniscript_expr.iter_pk().collect::<Vec<String>>(), | ||
vec!["@0/**", "@1/**"] | ||
); | ||
} | ||
} | ||
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// Unknown top-level fragment. | ||
assert_eq!( | ||
parse(&make_policy("unknown(pk(@0/**))", &[])).unwrap_err(), | ||
Error::InvalidInput, | ||
); | ||
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// Unknown script fragment. | ||
assert_eq!( | ||
parse(&make_policy("wsh(unknown(@0/**))", &[])).unwrap_err(), | ||
Error::InvalidInput, | ||
); | ||
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// Miniscript type-check fails (should be `or_b(pk(@0/**),s:pk(@1/**))`). | ||
assert_eq!( | ||
parse(&make_policy("wsh(or_b(pk(@0/**),pk(@1/**)))", &[])).unwrap_err(), | ||
Error::InvalidInput, | ||
); | ||
} | ||
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#[test] | ||
fn test_parse_validate() { | ||
let our_key = make_our_key(KEYPATH_ACCOUNT); | ||
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// All good. | ||
assert!(parse(&make_policy("wsh(pk(@0/**))", &[our_key.clone()])) | ||
.unwrap() | ||
.validate(BtcCoin::Tbtc) | ||
.is_ok()); | ||
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// Unsupported coins | ||
for coin in [BtcCoin::Btc, BtcCoin::Ltc, BtcCoin::Tltc] { | ||
assert_eq!( | ||
parse(&make_policy("wsh(pk(@0/**))", &[our_key.clone()])) | ||
.unwrap() | ||
.validate(coin), | ||
Err(Error::InvalidInput) | ||
); | ||
} | ||
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// Too many keys. | ||
let many_keys: Vec<pb::KeyOriginInfo> = (0..=20) | ||
.map(|i| make_our_key(&[48 + HARDENED, 1 + HARDENED, i + HARDENED, 3 + HARDENED])) | ||
.collect(); | ||
assert_eq!( | ||
parse(&make_policy("wsh(pk(@0/**))", &many_keys)) | ||
.unwrap() | ||
.validate(BtcCoin::Tbtc), | ||
Err(Error::InvalidInput) | ||
); | ||
} | ||
} |