Validate policy keys and hashes before compiling descriptors

CHANGELOG.md

@@ -14,6 +14,7 @@ page. See [DEVELOPMENT_CYCLE.md](DEVELOPMENT_CYCLE.md) for more details.
 - Rejected `--proxy` on the `rpc` backend, and unsupported proxy options (`--proxy_auth`, `--timeout`) on the `rpc` and `cbf` backends, instead of silently ignoring them
 - Fixed `compile` rejecting policies that are valid for the requested script type
 - Fixed `warn!` messages, including the mainnet notice, being hidden unless `RUST_LOG` was set; warnings are now shown by default
+- Fixed `compile` silently accepting placeholder keys/hashes instead of validating them; added `--placeholders` to opt back into the old permissive behavior
 
 ## [4.0.0]
 

src/handlers/descriptor.rs

@@ -22,7 +22,12 @@ use {
             key::{Parity, rand},
             secp256k1::{PublicKey, Scalar, Secp256k1, SecretKey},
         },
-        miniscript::{Descriptor, descriptor::TapTree, policy::Concrete},
+        miniscript::{
+            Descriptor, ForEachKey, FromStrKey, Legacy, MiniscriptKey, ScriptContext, Segwitv0,
+            Tap,
+            descriptor::{DescriptorPublicKey, TapTree},
+            policy::Concrete,
+        },
     },
     std::{str::FromStr, sync::Arc},
 };
@@ -80,6 +85,11 @@ pub struct CompileCommand {
         default_value_t = ScriptType::Wsh
     )]
     script_type: ScriptType,
+    /// Skip key and hash validation, accepting placeholders (e.g. pk(A)). Useful for
+    /// inspecting a policy's shape without real keys. Descriptors compiled with this
+    /// flag are not usable for spending.
+    #[arg(long = "placeholders")]
+    placeholders: bool,
 }
 
 /// Script types the compiled policy can be embedded in.
@@ -92,48 +102,99 @@ pub enum ScriptType {
     Tr,
 }
 
+#[cfg(feature = "compiler")]
+/// Rejects keys that parse fine on their own but aren't valid for `Ctx` (e.g. an
+/// x-only key under `Segwitv0`), which miniscript's compiler otherwise turns into
+/// a panic instead of an error. A no-op for `Pk = String`, since `String` never
+/// reports itself as uncompressed or x-only.
+fn check_policy_keys<Pk: MiniscriptKey, Ctx: ScriptContext>(
+    policy: &Concrete<Pk>,
+) -> Result<(), Error> {
+    let mut key_error = None;
+    policy.for_each_key(|pk| match Ctx::check_pk(pk) {
+        Ok(()) => true,
+        Err(e) => {
+            key_error = Some(e);
+            false
+        }
+    });
+
+    match key_error {
+        Some(e) => Err(Error::Generic(format!("Invalid policy: {e}"))),
+        None => Ok(()),
+    }
+}
+
+#[cfg(feature = "compiler")]
+/// Parses `policy_str` as `Pk` and compiles it for `script_type`. Returns the
+/// descriptor string and, for `tr`, the random tweak `r` used to derive the
+/// unspendable internal key so the caller can verify it.
+fn compile_policy<Pk: FromStrKey>(
+    policy_str: &str,
+    script_type: ScriptType,
+) -> Result<(String, Option<String>), Error> {
+    let policy: Concrete<Pk> = Concrete::from_str(policy_str)
+        .map_err(|e| Error::Generic(format!("Invalid policy: {e}")))?;
+
+    let mut r = None;
+
+    // Compile per branch, not once up front: the contexts have different script
+    // limits, and the narrowest one would reject policies valid for the requested type.
+    let descriptor = match script_type {
+        ScriptType::Sh => {
+            check_policy_keys::<Pk, Legacy>(&policy)?;
+            Descriptor::new_sh(policy.compile()?)
+        }
+        ScriptType::Wsh => {
+            check_policy_keys::<Pk, Segwitv0>(&policy)?;
+            Descriptor::new_wsh(policy.compile()?)
+        }
+        ScriptType::ShWsh => {
+            check_policy_keys::<Pk, Segwitv0>(&policy)?;
+            Descriptor::new_sh_wsh(policy.compile()?)
+        }
+        ScriptType::Tr => {
+            check_policy_keys::<Pk, Tap>(&policy)?;
+            // Use a randomized unspendable internal key (H + rG) instead of a fixed NUMS
+            // point. This improves privacy by preventing observers from determining whether
+            // key-path spending is disabled. `r` is returned so the user can verify the key
+            // is derived from the NUMS point. See BIP-341.
+            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)
+                .map_err(|e| Error::Generic(format!("Invalid NUMS key: {e}")))?;
+            let nums_point = PublicKey::from_x_only_public_key(nums_key, Parity::Even);
+
+            let internal_key_point = nums_point
+                .add_exp_tweak(&secp, &Scalar::from(r_secret))
+                .map_err(|e| Error::Generic(format!("Failed to tweak NUMS key: {e}")))?;
+            let (xonly_internal_key, _) = internal_key_point.x_only_public_key();
+
+            let tree = TapTree::Leaf(Arc::new(policy.compile()?));
+            let internal_key = Pk::from_str(&xonly_internal_key.to_string())
+                .map_err(|e| Error::Generic(format!("Failed to parse internal key: {e}")))?;
+            Descriptor::new_tr(internal_key, Some(tree))
+        }
+    }?;
+
+    Ok((descriptor.to_string(), r))
+}
+
 #[cfg(feature = "compiler")]
 impl AppCommand<AppContext<Init>> for CompileCommand {
     type Output = DescriptorResult;
 
     fn execute(&self, _ctx: &mut AppContext<Init>) -> Result<Self::Output, Error> {
-        let policy: Concrete<String> = Concrete::from_str(&self.policy)
-            .map_err(|e| Error::Generic(format!("Invalid policy: {e}")))?;
-
-        let mut r = None;
-
-        // Compile per branch, not once up front: the contexts have different script
-        // limits, and the narrowest one would reject policies valid for the requested type.
-        let descriptor = match self.script_type {
-            ScriptType::Sh => Descriptor::new_sh(policy.compile()?),
-            ScriptType::Wsh => Descriptor::new_wsh(policy.compile()?),
-            ScriptType::ShWsh => Descriptor::new_sh_wsh(policy.compile()?),
-            ScriptType::Tr => {
-                // Use a randomized unspendable internal key (H + rG) instead of a fixed NUMS
-                // point. This improves privacy by preventing observers from determining whether
-                // key-path spending is disabled. `r` is returned so the user can verify the key
-                // is derived from the NUMS point. See BIP-341.
-                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)
-                    .map_err(|e| Error::Generic(format!("Invalid NUMS key: {e}")))?;
-                let nums_point = PublicKey::from_x_only_public_key(nums_key, Parity::Even);
-
-                let internal_key_point =
-                    nums_point
-                        .add_exp_tweak(&secp, &Scalar::from(r_secret))
-                        .map_err(|e| Error::Generic(format!("Failed to tweak NUMS key: {e}")))?;
-                let (xonly_internal_key, _) = internal_key_point.x_only_public_key();
-
-                let tree = TapTree::Leaf(Arc::new(policy.compile()?));
-                Descriptor::new_tr(xonly_internal_key.to_string(), Some(tree))
-            }
-        }?;
+        let (descriptor, r) = if self.placeholders {
+            compile_policy::<String>(&self.policy, self.script_type)?
+        } else {
+            compile_policy::<DescriptorPublicKey>(&self.policy, self.script_type)?
+        };
 
         Ok(DescriptorResult {
-            descriptor: Some(descriptor.to_string()),
+            descriptor: Some(descriptor),
             mnemonic: None,
             multipath_descriptor: None,
             public_descriptors: None,

tests/integration/init.rs

@@ -223,6 +223,10 @@ mod test_compile {
 
     /// A policy can be valid for tr or wsh type and still exceed the limits of the
     /// legacy context, whose 520-byte redeemScript cap does not apply to it.
+    ///
+    /// Uses placeholder keys (K01, K02, ...) since only the policy's shape, not its
+    /// keys, matters for this test - `--placeholders` keeps that shape-only
+    /// intent even though real key validation is on by default.
     #[test]
     fn test_compile_policy_beyond_legacy_limits() {
         let temp_dir = TempDir::new().unwrap();
@@ -235,13 +239,13 @@ mod test_compile {
         let policy = format!("thresh(2,{keys})");
 
         // compile tr
-        cli.cmd("compile", &[&policy, "--type", "tr"])
+        cli.cmd("compile", &[&policy, "--type", "tr", "--placeholders"])
             .assert()
             .success()
             .stdout(predicate::str::contains("tr("));
 
         // compile wsh
-        cli.cmd("compile", &[&policy, "--type", "wsh"])
+        cli.cmd("compile", &[&policy, "--type", "wsh", "--placeholders"])
             .assert()
             .success()
             .stdout(predicate::str::contains("wsh("));
@@ -277,6 +281,86 @@ mod test_compile {
             .failure()
             .stderr(predicate::str::contains("Invalid policy"));
     }
+
+    #[test]
+    fn test_compile_rejects_placeholder_key_by_default() {
+        let temp_dir = TempDir::new().unwrap();
+        let cli = BdkCli::new("testnet", Some(temp_dir.path().to_path_buf()));
+
+        cli.cmd("compile", &["pk(ABC)", "--type", "wsh"])
+            .assert()
+            .failure()
+            .stderr(predicate::str::contains("Invalid policy"));
+    }
+
+    #[test]
+    fn test_compile_rejects_placeholder_hash_by_default() {
+        let temp_dir = TempDir::new().unwrap();
+        let cli = BdkCli::new("testnet", Some(temp_dir.path().to_path_buf()));
+
+        let policy =
+            "and(pk(02e5b88fdb71c696e1a473f309a47535b7190e21a22bd25e7fc8bd055db3bba12f),sha256(H))";
+
+        cli.cmd("compile", &[policy, "--type", "wsh"])
+            .assert()
+            .failure()
+            .stderr(predicate::str::contains("Invalid policy"));
+    }
+
+    #[test]
+    fn test_compile_allows_placeholder_key_with_flag() {
+        let temp_dir = TempDir::new().unwrap();
+        let cli = BdkCli::new("testnet", Some(temp_dir.path().to_path_buf()));
+
+        cli.cmd("compile", &["pk(ABC)", "--type", "wsh", "--placeholders"])
+            .assert()
+            .success()
+            .stdout(predicate::str::contains("wsh(pk(ABC))"));
+    }
+
+    #[test]
+    fn test_compile_accepts_xpub_key() {
+        let temp_dir = TempDir::new().unwrap();
+        let cli = BdkCli::new("testnet", Some(temp_dir.path().to_path_buf()));
+
+        let policy = "pk(xpub661MyMwAqRbcFtXgS5sYJABqqG9YLmC4Q1Rdap9gSE8NqtwybGhePY2gZ29ESFjqJoCu1Rupje8YtGqsefD265TMg7usUDFdp6W1EGMcet8/0/*)";
+
+        cli.cmd("compile", &[policy, "--type", "wsh"])
+            .assert()
+            .success()
+            .stdout(predicate::str::contains("wsh("));
+    }
+
+    /// An x-only key is only valid under `tr`. Compiling it as a real key for
+    /// `sh`/`wsh`/`sh-wsh` must return an error. Without the context check,
+    /// miniscript's compiler panics when `DescriptorPublicKey` reports an x-only key.
+    #[test]
+    fn test_compile_rejects_x_only_key_for_non_tr_types() {
+        let temp_dir = TempDir::new().unwrap();
+        let cli = BdkCli::new("testnet", Some(temp_dir.path().to_path_buf()));
+
+        let policy = "pk(50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0)";
+
+        for script_type in ["sh", "wsh", "sh-wsh"] {
+            cli.cmd("compile", &[policy, "--type", script_type])
+                .assert()
+                .failure()
+                .stderr(predicate::str::contains("Invalid policy"));
+        }
+    }
+
+    #[test]
+    fn test_compile_accepts_x_only_key_for_tr() {
+        let temp_dir = TempDir::new().unwrap();
+        let cli = BdkCli::new("testnet", Some(temp_dir.path().to_path_buf()));
+
+        let policy = "pk(50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0)";
+
+        cli.cmd("compile", &[policy, "--type", "tr"])
+            .assert()
+            .success()
+            .stdout(predicate::str::contains("tr("));
+    }
 }
 
 // --- CONFIG COMMAND TESTS ---