feat(compile): compile taproot descriptor with randomized unspendable internal key

Cargo.toml

@@ -60,3 +60,6 @@ verify = []
 # Extra utility tools
 # Compile policies
 compiler = []
+
+[dev-dependencies]
+shlex = "1.3.0"

src/error.rs

@@ -45,6 +45,9 @@ pub enum BDKCliError {
     #[error("Miniscript error: {0}")]
     MiniscriptError(#[from] bdk_wallet::miniscript::Error),
 
+    #[error("Miniscript compiler error: {0}")]
+    MiniscriptCompilerError(#[from] bdk_wallet::miniscript::policy::compiler::CompilerError),
+
     #[error("ParseError: {0}")]
     ParseError(#[from] bdk_wallet::bitcoin::address::ParseError),
 
@@ -78,6 +81,10 @@ pub enum BDKCliError {
     #[error("Signer error: {0}")]
     SignerError(#[from] bdk_wallet::signer::SignerError),
 
+    #[cfg(feature = "compiler")]
+    #[error("Secp256k1 error: {0}")]
+    Secp256k1Error(#[from] bdk_wallet::bitcoin::secp256k1::Error),
+
     #[cfg(feature = "electrum")]
     #[error("Electrum error: {0}")]
     Electrum(#[from] bdk_electrum::electrum_client::Error),

src/handlers.rs

@@ -37,12 +37,18 @@ use bdk_wallet::miniscript::miniscript;
 #[cfg(feature = "sqlite")]
 use bdk_wallet::rusqlite::Connection;
 use bdk_wallet::{KeychainKind, SignOptions, Wallet};
+
 #[cfg(feature = "compiler")]
 use bdk_wallet::{
-    bitcoin::XOnlyPublicKey,
+    bitcoin::{
+        XOnlyPublicKey,
+        key::{Parity, rand},
+        secp256k1::{PublicKey, Scalar, SecretKey},
+    },
     descriptor::{Descriptor, Legacy, Miniscript},
     miniscript::{Tap, descriptor::TapTree, policy::Concrete},
 };
+
 use cli_table::{Cell, CellStruct, Style, Table, format::Justify};
 use serde_json::json;
 #[cfg(feature = "cbf")]
@@ -893,50 +899,62 @@ pub(crate) fn handle_compile_subcommand(
     pretty: bool,
 ) -> Result<String, Error> {
     let policy = Concrete::<String>::from_str(policy.as_str())?;
-    let legacy_policy: Miniscript<String, Legacy> = policy
-        .compile()
-        .map_err(|e| Error::Generic(e.to_string()))?;
-    let segwit_policy: Miniscript<String, Segwitv0> = policy
-        .compile()
-        .map_err(|e| Error::Generic(e.to_string()))?;
-    let taproot_policy: Miniscript<String, Tap> = policy
-        .compile()
-        .map_err(|e| Error::Generic(e.to_string()))?;
+
+    let legacy_policy: Miniscript<String, Legacy> = policy.compile()?;
+    let segwit_policy: Miniscript<String, Segwitv0> = policy.compile()?;
+    let taproot_policy: Miniscript<String, Tap> = policy.compile()?;
+
+    let mut r = None;
 
     let descriptor = match script_type.as_str() {
         "sh" => Descriptor::new_sh(legacy_policy),
         "wsh" => Descriptor::new_wsh(segwit_policy),
         "sh-wsh" => Descriptor::new_sh_wsh(segwit_policy),
         "tr" => {
-            // For tr descriptors, we use a well-known unspendable key (NUMS point).
-            // This ensures the key path is effectively disabled and only script path can be used.
-            // See https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki#constructing-and-spending-taproot-outputs
+            // For tr descriptors, we use a randomized unspendable key (H + rG).
+            // This improves privacy by preventing observers from determining if key path spending is disabled.
+            // See BIP-341: https://github.com/bitcoin/bips/blob/master/bip-0341.mediawiki#constructing-and-spending-taproot-outputs
+
+            let secp = Secp256k1::new();
+            let r_secret = SecretKey::new(&mut rand::thread_rng());
+            r = Some(r_secret.display_secret().to_string());
+
+            let nums_key = XOnlyPublicKey::from_str(NUMS_UNSPENDABLE_KEY_HEX)?;
+            let nums_point = PublicKey::from_x_only_public_key(nums_key, Parity::Even);
 
-            let xonly_public_key = XOnlyPublicKey::from_str(NUMS_UNSPENDABLE_KEY_HEX)
-                .map_err(|e| Error::Generic(format!("Invalid NUMS key: {e}")))?;
+            let internal_key_point = nums_point.add_exp_tweak(&secp, &Scalar::from(r_secret))?;
+            let (xonly_internal_key, _) = internal_key_point.x_only_public_key();
 
             let tree = TapTree::Leaf(Arc::new(taproot_policy));
-            Descriptor::new_tr(xonly_public_key.to_string(), Some(tree))
+            Descriptor::new_tr(xonly_internal_key.to_string(), Some(tree))
         }
         _ => {
             return Err(Error::Generic(
                 "Invalid script type. Supported types: sh, wsh, sh-wsh, tr".to_string(),
             ));
         }
-    }?;
+    }?
+    .to_string();
+
     if pretty {
-        let table = vec![vec![
-            "Descriptor".cell().bold(true),
-            descriptor.to_string().cell(),
-        ]]
-        .table()
-        .display()
-        .map_err(|e| Error::Generic(e.to_string()))?;
+        let mut rows = vec![vec!["Descriptor".cell().bold(true), descriptor.cell()]];
+
+        if let Some(r_value) = &r {
+            rows.push(vec!["r".cell().bold(true), r_value.cell()]);
+        }
+
+        let table = rows
+            .table()
+            .display()
+            .map_err(|e| Error::Generic(e.to_string()))?;
+
         Ok(format!("{table}"))
     } else {
-        Ok(serde_json::to_string_pretty(
-            &json!({"descriptor": descriptor.to_string()}),
-        )?)
+        let mut output = json!({"descriptor": descriptor});
+        if let Some(r_value) = r {
+            output["r"] = json!(r_value);
+        }
+        Ok(serde_json::to_string_pretty(&output)?)
     }
 }
 
@@ -1450,92 +1468,4 @@ mod test {
         let full_signed_psbt = Psbt::from_str("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").unwrap();
         assert!(is_final(&full_signed_psbt).is_ok());
     }
-
-    #[cfg(feature = "compiler")]
-    #[test]
-    fn test_compile_taproot() {
-        use super::{NUMS_UNSPENDABLE_KEY_HEX, handle_compile_subcommand};
-        use bdk_wallet::bitcoin::Network;
-
-        // Expected taproot descriptors with checksums (using NUMS key from constant)
-        let expected_pk_a = format!("tr({},pk(A))#a2mlskt0", NUMS_UNSPENDABLE_KEY_HEX);
-        let expected_and_ab = format!(
-            "tr({},and_v(v:pk(A),pk(B)))#sfplm6kv",
-            NUMS_UNSPENDABLE_KEY_HEX
-        );
-
-        // Test simple pk policy compilation to taproot
-        let result = handle_compile_subcommand(
-            Network::Testnet,
-            "pk(A)".to_string(),
-            "tr".to_string(),
-            false,
-        );
-        assert!(result.is_ok());
-        let json_string = result.unwrap();
-        let json_result: serde_json::Value = serde_json::from_str(&json_string).unwrap();
-        let descriptor = json_result.get("descriptor").unwrap().as_str().unwrap();
-        assert_eq!(descriptor, expected_pk_a);
-
-        // Test more complex policy
-        let result = handle_compile_subcommand(
-            Network::Testnet,
-            "and(pk(A),pk(B))".to_string(),
-            "tr".to_string(),
-            false,
-        );
-        assert!(result.is_ok());
-        let json_string = result.unwrap();
-        let json_result: serde_json::Value = serde_json::from_str(&json_string).unwrap();
-        let descriptor = json_result.get("descriptor").unwrap().as_str().unwrap();
-        assert_eq!(descriptor, expected_and_ab);
-    }
-
-    #[cfg(feature = "compiler")]
-    #[test]
-    fn test_compile_invalid_cases() {
-        use super::handle_compile_subcommand;
-        use bdk_wallet::bitcoin::Network;
-
-        // Test invalid policy syntax
-        let result = handle_compile_subcommand(
-            Network::Testnet,
-            "invalid_policy".to_string(),
-            "tr".to_string(),
-            false,
-        );
-        assert!(result.is_err());
-
-        // Test invalid script type
-        let result = handle_compile_subcommand(
-            Network::Testnet,
-            "pk(A)".to_string(),
-            "invalid_type".to_string(),
-            false,
-        );
-        assert!(result.is_err());
-
-        // Test empty policy
-        let result =
-            handle_compile_subcommand(Network::Testnet, "".to_string(), "tr".to_string(), false);
-        assert!(result.is_err());
-
-        // Test malformed policy with unmatched parentheses
-        let result = handle_compile_subcommand(
-            Network::Testnet,
-            "pk(A".to_string(),
-            "tr".to_string(),
-            false,
-        );
-        assert!(result.is_err());
-
-        // Test policy with unknown function
-        let result = handle_compile_subcommand(
-            Network::Testnet,
-            "unknown_func(A)".to_string(),
-            "tr".to_string(),
-            false,
-        );
-        assert!(result.is_err());
-    }
 }

tests/compile.rs

@@ -0,0 +1,70 @@
+// Copyright (c) 2020-2025 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Compile Command Tests
+//!
+//! Tests for compile command and subcommands
+
+use std::process::Command;
+
+fn run_cmd(cmd: &str) -> Result<String, String> {
+    let full_cmd = format!("run --features compiler -- {}", cmd);
+    let args = shlex::split(&full_cmd).unwrap();
+
+    let output = Command::new("cargo").args(args).output().unwrap();
+    let stdout = String::from_utf8_lossy(&output.stdout).to_string();
+    let stderr = String::from_utf8_lossy(&output.stderr).to_string();
+
+    if output.status.success() {
+        Ok(stdout)
+    } else {
+        Err(stderr)
+    }
+}
+
+#[test]
+fn test_compile_taproot() {
+    let stdout = run_cmd(r#"compile "pk(ABC)" -t tr"#).unwrap();
+    let json: serde_json::Value = serde_json::from_str(&stdout).unwrap();
+
+    assert!(json.get("descriptor").is_some());
+    assert!(json.get("r").is_some());
+}
+
+#[test]
+fn test_compile_sh() {
+    let stdout = run_cmd(r#"compile "pk(ABC)" -t sh"#).unwrap();
+    let json: serde_json::Value = serde_json::from_str(&stdout).unwrap();
+
+    assert!(json.get("descriptor").is_some());
+    assert!(json.get("r").is_none());
+}
+
+#[test]
+fn test_invalid_cases() {
+    // Test invalid policy syntax
+    let stderr = run_cmd(r#"compile "invalid_policy""#).unwrap_err();
+    assert!(stderr.contains("Miniscript error"));
+
+    // Test invalid script type
+    let stderr = run_cmd(r#"compile "pk(A)" -t invalid_type"#).unwrap_err();
+    assert!(stderr.contains("error: invalid value 'invalid_type' for '--type <SCRIPT_TYPE>'"));
+
+    // Test empty policy
+    let stderr = run_cmd("compile").unwrap_err();
+    assert!(stderr.contains("error: the following required arguments were not provided"));
+    assert!(stderr.contains("<POLICY>"));
+
+    // Test malformed policy with unmatched parentheses
+    let stderr = run_cmd(r#"compile "pk(A""#).unwrap_err();
+    assert!(stderr.contains("Miniscript error: expected )"));
+
+    // Test policy with unknown function
+    let stderr = run_cmd(r#"compile "unknown_func(A)""#).unwrap_err();
+    assert!(stderr.contains("Miniscript error: unexpected «unknown_func»"));
+}