add(chain): Adds `ViewingKey` type in zebra-chain (#8198)

* adds/impls types in zebra-chain to be used by the zebra-scan RPC server

* Adds methods for parsing and a test

* adds test for key hash encoding

* Apply suggestions from code review

Co-authored-by: Marek <mail@marek.onl>

* refactors viewing key type

* refactors/renames for viewing keys

* fixes doc links

* Apply suggestions from code review

* Apply suggestions from code review

* removes ViewingKeyHash and ViewingKeyWithHash types

* removes `to_bytes` methods

* remove outdated method and call

---------

Co-authored-by: Marek <mail@marek.onl>

Cargo.lock

@@ -5709,6 +5709,7 @@ dependencies = [
  "uint",
  "x25519-dalek",
  "zcash_address",
+ "zcash_client_backend",
  "zcash_encoding",
  "zcash_history",
  "zcash_note_encryption",

zebra-chain/Cargo.toml

@@ -34,6 +34,11 @@ getblocktemplate-rpcs = [
     "zcash_address",
 ]
 
+# Experimental shielded scanning support
+shielded-scan = [
+    "zcash_client_backend"
+]
+
 # Experimental internal miner support
 # TODO: Internal miner feature functionality was removed at https://github.com/ZcashFoundation/zebra/issues/8180
 #       See what was removed at https://github.com/ZcashFoundation/zebra/blob/v1.5.1/zebra-chain/Cargo.toml#L38-L43
@@ -127,9 +132,12 @@ serde_json = { version = "1.0.113", optional = true }
 # Production feature async-error and testing feature proptest-impl
 tokio = { version = "1.35.1", optional = true }
 
-# Experimental feature getblocktemplate-rpcs
+# Production feature getblocktemplate-rpcs
 zcash_address = { version = "0.3.1", optional = true }
 
+# Experimental feature shielded-scan
+zcash_client_backend = { version = "0.10.0-rc.1", optional = true }
+
 # Optional testing dependencies
 proptest = { version = "1.4.0", optional = true }
 proptest-derive = { version = "0.4.0", optional = true }

zebra-chain/src/primitives.rs

@@ -12,6 +12,9 @@ mod address;
 #[cfg(feature = "getblocktemplate-rpcs")]
 pub use address::Address;
 
+#[cfg(feature = "shielded-scan")]
+pub mod viewing_key;
+
 pub mod byte_array;
 
 pub use ed25519_zebra as ed25519;

zebra-chain/src/primitives/viewing_key.rs

@@ -0,0 +1,43 @@
+//! Type definitions for viewing keys and their hashes.
+
+use crate::parameters::Network;
+
+mod orchard;
+mod sapling;
+
+use orchard::OrchardViewingKey;
+use sapling::SaplingViewingKey;
+
+#[cfg(test)]
+mod tests;
+
+/// A Zcash Sapling or Orchard viewing key
+#[derive(Debug, Clone)]
+pub enum ViewingKey {
+    /// A viewing key for Sapling
+    Sapling(SaplingViewingKey),
+
+    /// A viewing key for Orchard
+    Orchard(OrchardViewingKey),
+}
+
+impl ViewingKey {
+    /// Accepts an encoded Sapling viewing key to decode
+    ///
+    /// Returns a [`ViewingKey`] if successful, or None otherwise
+    fn parse_sapling(sapling_key: &str, network: Network) -> Option<Self> {
+        SaplingViewingKey::parse(sapling_key, network).map(Self::Sapling)
+    }
+
+    /// Accepts an encoded Orchard viewing key to decode
+    ///
+    /// Returns a [`ViewingKey`] if successful, or None otherwise
+    fn parse_orchard(sapling_key: &str, network: Network) -> Option<Self> {
+        OrchardViewingKey::parse(sapling_key, network).map(Self::Orchard)
+    }
+
+    /// Parses an encoded viewing key and returns it as a [`ViewingKey`] type.
+    pub fn parse(key: &str, network: Network) -> Option<Self> {
+        Self::parse_sapling(key, network).or_else(|| Self::parse_orchard(key, network))
+    }
+}

zebra-chain/src/primitives/viewing_key/orchard.rs

@@ -0,0 +1,17 @@
+//! Defines types and implements methods for parsing Orchard viewing keys and converting them to `zebra-chain` types
+
+use crate::parameters::Network;
+
+/// A Zcash Orchard viewing key
+#[derive(Debug, Clone)]
+pub enum OrchardViewingKey {}
+
+impl OrchardViewingKey {
+    /// Accepts an encoded Orchard viewing key to decode
+    ///
+    /// Returns a [`OrchardViewingKey`] if successful, or None otherwise
+    pub fn parse(_key: &str, _network: Network) -> Option<Self> {
+        // TODO: parse Orchard viewing keys
+        None
+    }
+}

zebra-chain/src/primitives/viewing_key/sapling.rs

@@ -0,0 +1,87 @@
+//! Defines types and implements methods for parsing Sapling viewing keys and converting them to `zebra-chain` types
+
+use zcash_client_backend::encoding::decode_extended_full_viewing_key;
+use zcash_primitives::{
+    constants::*,
+    sapling::keys::{FullViewingKey as SaplingFvk, SaplingIvk},
+    zip32::DiversifiableFullViewingKey as SaplingDfvk,
+};
+
+use crate::parameters::Network;
+
+/// A Zcash Sapling viewing key
+#[derive(Debug, Clone)]
+pub enum SaplingViewingKey {
+    /// An incoming viewing key for Sapling
+    Ivk(Box<SaplingIvk>),
+
+    /// A full viewing key for Sapling
+    Fvk(Box<SaplingFvk>),
+
+    /// A diversifiable full viewing key for Sapling
+    Dfvk(Box<SaplingDfvk>),
+}
+
+impl SaplingViewingKey {
+    /// Accepts an encoded Sapling extended full viewing key to decode
+    ///
+    /// Returns a [`SaplingViewingKey::Dfvk`] if successful, or None otherwise
+    fn parse_extended_full_viewing_key(sapling_key: &str, network: Network) -> Option<Self> {
+        decode_extended_full_viewing_key(network.sapling_efvk_hrp(), sapling_key)
+            // this should fail often, so a debug-level log is okay
+            .map_err(|err| debug!(?err, "could not decode Sapling extended full viewing key"))
+            .ok()
+            .map(|efvk| Box::new(efvk.to_diversifiable_full_viewing_key()))
+            .map(Self::Dfvk)
+    }
+
+    /// Accepts an encoded Sapling diversifiable full viewing key to decode
+    ///
+    /// Returns a [`SaplingViewingKey::Dfvk`] if successful, or None otherwise
+    fn parse_diversifiable_full_viewing_key(_sapling_key: &str, _network: Network) -> Option<Self> {
+        // TODO: Parse Sapling diversifiable full viewing key
+        None
+    }
+
+    /// Accepts an encoded Sapling full viewing key to decode
+    ///
+    /// Returns a [`SaplingViewingKey::Fvk`] if successful, or None otherwise
+    fn parse_full_viewing_key(_sapling_key: &str, _network: Network) -> Option<Self> {
+        // TODO: Parse Sapling full viewing key
+        None
+    }
+
+    /// Accepts an encoded Sapling incoming viewing key to decode
+    ///
+    /// Returns a [`SaplingViewingKey::Ivk`] if successful, or None otherwise
+    fn parse_incoming_viewing_key(_sapling_key: &str, _network: Network) -> Option<Self> {
+        // TODO: Parse Sapling incoming viewing key
+        None
+    }
+
+    /// Accepts an encoded Sapling viewing key to decode
+    ///
+    /// Returns a [`SaplingViewingKey`] if successful, or None otherwise
+    pub(super) fn parse(key: &str, network: Network) -> Option<Self> {
+        // TODO: Try types with prefixes first if some don't have prefixes?
+        Self::parse_extended_full_viewing_key(key, network)
+            .or_else(|| Self::parse_diversifiable_full_viewing_key(key, network))
+            .or_else(|| Self::parse_full_viewing_key(key, network))
+            .or_else(|| Self::parse_incoming_viewing_key(key, network))
+    }
+}
+
+impl Network {
+    /// Returns the human-readable prefix for an Zcash Sapling extended full viewing key
+    /// for this network.
+    fn sapling_efvk_hrp(&self) -> &'static str {
+        if self.is_a_test_network() {
+            // Assume custom testnets have the same HRP
+            //
+            // TODO: add the regtest HRP here
+            testnet::HRP_SAPLING_EXTENDED_FULL_VIEWING_KEY
+        } else {
+            mainnet::HRP_SAPLING_EXTENDED_FULL_VIEWING_KEY
+        }
+    }
+}

zebra-chain/src/primitives/viewing_key/tests.rs

@@ -0,0 +1,15 @@
+//! Tests for zebra-chain viewing key hashes
+
+use super::*;
+
+/// The extended Sapling viewing key of [ZECpages](https://zecpages.com/boardinfo)
+pub const ZECPAGES_SAPLING_VIEWING_KEY: &str = "zxviews1q0duytgcqqqqpqre26wkl45gvwwwd706xw608hucmvfalr759ejwf7qshjf5r9aa7323zulvz6plhttp5mltqcgs9t039cx2d09mgq05ts63n8u35hyv6h9nc9ctqqtue2u7cer2mqegunuulq2luhq3ywjcz35yyljewa4mgkgjzyfwh6fr6jd0dzd44ghk0nxdv2hnv4j5nxfwv24rwdmgllhe0p8568sgqt9ckt02v2kxf5ahtql6s0ltjpkckw8gtymxtxuu9gcr0swvz";
+
+/// Tests that `ViewingKey::parse` successfully decodes the zecpages sapling extended full viewing key
+#[test]
+fn parses_sapling_efvk_correctly() {
+    let _init_guard = zebra_test::init();
+
+    ViewingKey::parse(ZECPAGES_SAPLING_VIEWING_KEY, Network::Mainnet)
+        .expect("should parse hard-coded viewing key successfully");
+}

zebra-scan/src/scan.rs

@@ -288,8 +288,9 @@ pub fn scan_block<K: ScanningKey>(
 /// Currently only accepts extended full viewing keys, and returns both their diversifiable full
 /// viewing key and their individual viewing key, for testing purposes.
 ///
-/// TODO: work out what string format is used for SaplingIvk, if any, and support it here
-///       performance: stop returning both the dfvk and ivk for the same key
+// TODO: work out what string format is used for SaplingIvk, if any, and support it here
+//       performance: stop returning both the dfvk and ivk for the same key
+// TODO: use `ViewingKey::parse` from zebra-chain instead
 pub fn sapling_key_to_scan_block_keys(
     sapling_key: &SaplingScanningKey,
     network: Network,