pczt: Add a Redactor role

pczt/CHANGELOG.md

@@ -7,6 +7,9 @@ and this library adheres to Rust's notion of
 
 ## [Unreleased]
 
+### Added
+- `pczt::roles::redactor`
+
 ### Changed
 - Migrated to `nonempty 0.11`
 

pczt/src/lib.rs

@@ -16,6 +16,11 @@
 //! - Updater (anyone can contribute)
 //!   - Adds information necessary for subsequent entities to proceed, such as key paths
 //!     for signing spends.
+//! - Redactor (anyone can execute)
+//!   - Removes information that is unnecessary for subsequent entities to proceed.
+//!   - This can be useful e.g. when creating a transaction that has inputs from multiple
+//!     independent Signers; each can receive a PCZT with just the information they need
+//!     to sign, but (e.g.) not the `alpha` values for other Signers.
 //! - Prover (capability holders can contribute)
 //!   - Needs all private information for a single spend or output.
 //!   - In practice, the Updater that adds a given spend or output will either act as

pczt/src/roles.rs

@@ -7,6 +7,8 @@ pub mod verifier;
 
 pub mod updater;
 
+pub mod redactor;
+
 #[cfg(feature = "prover")]
 pub mod prover;
 

pczt/src/roles/redactor/mod.rs

@@ -0,0 +1,45 @@
+use crate::{common::Global, Pczt};
+
+pub mod orchard;
+pub mod sapling;
+pub mod transparent;
+
+pub struct Redactor {
+    pczt: Pczt,
+}
+
+impl Redactor {
+    /// Instantiates the Redactor role with the given PCZT.
+    pub fn new(pczt: Pczt) -> Self {
+        Self { pczt }
+    }
+
+    /// Redacts the global transaction details with the given closure.
+    pub fn redact_global_with<F>(mut self, f: F) -> Self
+    where
+        F: FnOnce(GlobalRedactor<'_>),
+    {
+        f(GlobalRedactor(&mut self.pczt.global));
+        self
+    }
+
+    /// Finishes the Redactor role, returning the redacted PCZT.
+    pub fn finish(self) -> Pczt {
+        self.pczt
+    }
+}
+
+/// An Redactor for the global transaction details.
+pub struct GlobalRedactor<'a>(&'a mut Global);
+
+impl<'a> GlobalRedactor<'a> {
+    /// Redacts the proprietary value at the given key.
+    pub fn redact_proprietary(&mut self, key: &str) {
+        self.0.proprietary.remove(key);
+    }
+
+    /// Removes all proprietary values.
+    pub fn clear_proprietary(&mut self) {
+        self.0.proprietary.clear();
+    }
+}

pczt/src/roles/redactor/orchard.rs

@@ -0,0 +1,222 @@
+use crate::orchard::{Action, Bundle};
+
+impl super::Redactor {
+    /// Redacts the Orchard bundle with the given closure.
+    pub fn redact_orchard_with<F>(mut self, f: F) -> Self
+    where
+        F: FnOnce(OrchardRedactor<'_>),
+    {
+        f(OrchardRedactor(&mut self.pczt.orchard));
+        self
+    }
+}
+
+/// A Redactor for the Orchard bundle.
+pub struct OrchardRedactor<'a>(&'a mut Bundle);
+
+impl<'a> OrchardRedactor<'a> {
+    /// Redacts all actions in the same way.
+    pub fn redact_actions<F>(&mut self, f: F)
+    where
+        F: FnOnce(ActionRedactor<'_>),
+    {
+        f(ActionRedactor(Actions::All(&mut self.0.actions)));
+    }
+
+    /// Redacts the action at the given index.
+    ///
+    /// Does nothing if the index is out of range.
+    pub fn redact_action<F>(&mut self, index: usize, f: F)
+    where
+        F: FnOnce(ActionRedactor<'_>),
+    {
+        if let Some(action) = self.0.actions.get_mut(index) {
+            f(ActionRedactor(Actions::One(action)));
+        }
+    }
+
+    /// Removes the proof.
+    pub fn clear_zkproof(&mut self) {
+        self.0.zkproof = None;
+    }
+
+    /// Removes the proof.
+    pub fn clear_bsk(&mut self) {
+        self.0.bsk = None;
+    }
+}
+
+/// A Redactor for Orchard actions.
+pub struct ActionRedactor<'a>(Actions<'a>);
+
+enum Actions<'a> {
+    All(&'a mut [Action]),
+    One(&'a mut Action),
+}
+
+impl<'a> ActionRedactor<'a> {
+    fn redact<F>(&mut self, f: F)
+    where
+        F: Fn(&mut Action),
+    {
+        match &mut self.0 {
+            Actions::All(actions) => {
+                for action in actions.iter_mut() {
+                    f(action);
+                }
+            }
+            Actions::One(action) => {
+                f(action);
+            }
+        }
+    }
+
+    /// Removes the spend authorizing signature.
+    pub fn clear_spend_auth_sig(&mut self) {
+        self.redact(|action| {
+            action.spend.spend_auth_sig = None;
+        });
+    }
+
+    /// Removes the spend's recipient.
+    pub fn clear_spend_recipient(&mut self) {
+        self.redact(|action| {
+            action.spend.recipient = None;
+        });
+    }
+
+    /// Removes the spend's value.
+    pub fn clear_spend_value(&mut self) {
+        self.redact(|action| {
+            action.spend.value = None;
+        });
+    }
+
+    /// Removes the rho value for the note being spent.
+    pub fn clear_spend_rho(&mut self) {
+        self.redact(|action| {
+            action.spend.rho = None;
+        });
+    }
+
+    /// Removes the seed randomness for the note being spent.
+    pub fn clear_spend_rseed(&mut self) {
+        self.redact(|action| {
+            action.spend.rseed = None;
+        });
+    }
+
+    /// Removes the spend's full viewing key.
+    pub fn clear_spend_fvk(&mut self) {
+        self.redact(|action| {
+            action.spend.fvk = None;
+        });
+    }
+
+    /// Removes the witness from the spent note to the bundle's anchor.
+    pub fn clear_spend_witness(&mut self) {
+        self.redact(|action| {
+            action.spend.witness = None;
+        });
+    }
+
+    /// Removes the spend authorization randomizer.
+    pub fn clear_spend_alpha(&mut self) {
+        self.redact(|action| {
+            action.spend.alpha = None;
+        });
+    }
+
+    /// Removes the ZIP 32 derivation path at which the spending key can be found for the
+    /// note being spent.
+    pub fn clear_spend_zip32_derivation(&mut self) {
+        self.redact(|action| {
+            action.spend.zip32_derivation = None;
+        });
+    }
+
+    /// Removes the spending key for this spent note, if it is a dummy note.
+    pub fn clear_spend_dummy_sk(&mut self) {
+        self.redact(|action| {
+            action.spend.dummy_sk = None;
+        });
+    }
+
+    /// Redacts the spend-specific proprietary value at the given key.
+    pub fn redact_spend_proprietary(&mut self, key: &str) {
+        self.redact(|action| {
+            action.spend.proprietary.remove(key);
+        });
+    }
+
+    /// Removes all spend-specific proprietary values.
+    pub fn clear_spend_proprietary(&mut self) {
+        self.redact(|action| {
+            action.spend.proprietary.clear();
+        });
+    }
+
+    /// Removes the output's recipient.
+    pub fn clear_output_recipient(&mut self) {
+        self.redact(|action| {
+            action.output.recipient = None;
+        });
+    }
+
+    /// Removes the output's value.
+    pub fn clear_output_value(&mut self) {
+        self.redact(|action| {
+            action.output.value = None;
+        });
+    }
+
+    /// Removes the seed randomness for the note being created.
+    pub fn clear_output_rseed(&mut self) {
+        self.redact(|action| {
+            action.output.rseed = None;
+        });
+    }
+
+    /// Removes the `ock` value used to encrypt `out_ciphertext`.
+    pub fn clear_output_ock(&mut self) {
+        self.redact(|action| {
+            action.output.ock = None;
+        });
+    }
+
+    /// Removes the ZIP 32 derivation path at which the spending key can be found for the
+    /// note being created.
+    pub fn clear_output_zip32_derivation(&mut self) {
+        self.redact(|action| {
+            action.output.zip32_derivation = None;
+        });
+    }
+
+    /// Removes the user-facing address to which the output is being sent, if any.
+    pub fn clear_output_user_address(&mut self) {
+        self.redact(|spend| {
+            spend.output.user_address = None;
+        });
+    }
+
+    /// Redacts the output-specific proprietary value at the given key.
+    pub fn redact_output_proprietary(&mut self, key: &str) {
+        self.redact(|action| {
+            action.output.proprietary.remove(key);
+        });
+    }
+
+    /// Removes all output-specific proprietary values.
+    pub fn clear_output_proprietary(&mut self) {
+        self.redact(|action| {
+            action.output.proprietary.clear();
+        });
+    }
+
+    /// Removes the value commitment randomness.
+    pub fn clear_rcv(&mut self) {
+        self.redact(|action| {
+            action.rcv = None;
+        });
+    }
+}