bitcoin: pre-process script configs

By converting the script configs into a parsed/validated form, we gain
the following advantages:

- for policies, we only parse/validate it once per tx, instead of also
twice per input (compute pk_script, compute sighash_script), and twice for each change output (to
check if it is really change and to compute the payload), making
policy transactions much more efficient
- the match patterns are much simpler as it removes SimpleType parsing
and all the protobuf nesting and unreachable `_ => ...` patterns
- we will be able to check if the script config is a Taproot policy in `is_taproot()`
without parsing it once more once we add Taproot policies

Author: benma

src/rust/bitbox02-rust/src/hww/api/bitcoin.rs

@@ -25,6 +25,7 @@ mod payment_request;
 mod policies;
 mod registration;
 mod script;
+mod script_configs;
 pub mod signmsg;
 pub mod signtx;
 

src/rust/bitbox02-rust/src/hww/api/bitcoin/common.rs

@@ -24,6 +24,7 @@ use pb::btc_script_config::SimpleType;
 pub use pb::btc_sign_init_request::FormatUnit;
 pub use pb::{BtcCoin, BtcOutputType};
 
+use super::script_configs::{ValidatedScriptConfig, ValidatedScriptConfigWithKeypath};
 use super::{multisig, params::Params, script};
 
 use sha2::{Digest, Sha256};
@@ -169,39 +170,19 @@ impl Payload {
         xpub_cache: &mut Bip32XpubCache,
         params: &Params,
         keypath: &[u32],
-        script_config_account: &pb::BtcScriptConfigWithKeypath,
+        script_config_account: &ValidatedScriptConfigWithKeypath,
     ) -> Result<Self, Error> {
-        match script_config_account {
-            pb::BtcScriptConfigWithKeypath {
-                script_config:
-                    Some(pb::BtcScriptConfig {
-                        config: Some(pb::btc_script_config::Config::SimpleType(simple_type)),
-                    }),
-                ..
-            } => {
-                let simple_type = pb::btc_script_config::SimpleType::try_from(*simple_type)?;
-                Self::from_simple(xpub_cache, params, simple_type, keypath)
+        match &script_config_account.config {
+            ValidatedScriptConfig::SimpleType(simple_type) => {
+                Self::from_simple(xpub_cache, params, *simple_type, keypath)
             }
-            pb::BtcScriptConfigWithKeypath {
-                script_config:
-                    Some(pb::BtcScriptConfig {
-                        config: Some(pb::btc_script_config::Config::Multisig(multisig)),
-                    }),
-                ..
-            } => Self::from_multisig(
+            ValidatedScriptConfig::Multisig(multisig) => Self::from_multisig(
                 params,
                 multisig,
                 keypath[keypath.len() - 2],
                 keypath[keypath.len() - 1],
             ),
-            pb::BtcScriptConfigWithKeypath {
-                script_config:
-                    Some(pb::BtcScriptConfig {
-                        config: Some(pb::btc_script_config::Config::Policy(policy)),
-                    }),
-                ..
-            } => Self::from_policy(&super::policies::parse(policy)?, keypath),
-            _ => Err(Error::InvalidInput),
+            ValidatedScriptConfig::Policy(policy) => Self::from_policy(policy, keypath),
         }
     }
 

src/rust/bitbox02-rust/src/hww/api/bitcoin/script_configs.rs

@@ -0,0 +1,31 @@
+// Copyright 2024 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.
+
+use super::pb;
+use pb::btc_script_config::{Multisig, SimpleType};
+
+use super::policies::ParsedPolicy;
+
+/// Parsed and validated form of `pb::BtcScriptConfig`.
+pub enum ValidatedScriptConfig<'a> {
+    SimpleType(SimpleType),
+    Multisig(&'a Multisig),
+    Policy(ParsedPolicy<'a>),
+}
+
+/// Parsed and validated form of `pb::BtcScriptConfigWithKeypath`.
+pub struct ValidatedScriptConfigWithKeypath<'a> {
+    pub keypath: &'a [u32],
+    pub config: ValidatedScriptConfig<'a>,
+}