Wallet spending key derivation path

Cargo.lock

@@ -511,6 +511,9 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "zcash_client_backend"
 version = "0.0.0"
+dependencies = [
+ "zcash_primitives 0.0.0",
+]
 
 [[package]]
 name = "zcash_primitives"

zcash_client_backend/Cargo.toml

@@ -7,3 +7,4 @@ authors = [
 edition = "2018"
 
 [dependencies]
+zcash_primitives = { path = "../zcash_primitives" }

zcash_client_backend/src/constants.rs

@@ -0,0 +1,4 @@
+//! Zcash global and per-network constants.
+
+pub mod mainnet;
+pub mod testnet;

zcash_client_backend/src/constants/mainnet.rs

@@ -0,0 +1,4 @@
+/// The mainnet coin type for ZEC, as defined by [SLIP 44].
+///
+/// [SLIP 44]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
+pub const COIN_TYPE: u32 = 133;

zcash_client_backend/src/constants/testnet.rs

@@ -0,0 +1,4 @@
+/// The testnet coin type for ZEC, as defined by [SLIP 44].
+///
+/// [SLIP 44]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
+pub const COIN_TYPE: u32 = 1;

zcash_client_backend/src/keys.rs

@@ -0,0 +1,24 @@
+//! Helper functions for managing light client key material.
+
+use zcash_primitives::zip32::{ChildIndex, ExtendedSpendingKey};
+
+/// Derives the ZIP 32 [`ExtendedSpendingKey`] for a given coin type and account from the
+/// given seed.
+///
+/// # Examples
+///
+/// ```
+/// use zcash_client_backend::{constants::testnet::COIN_TYPE, keys::spending_key};
+///
+/// let extsk = spending_key(&[0; 32][..], COIN_TYPE, 0);
+/// ```
+pub fn spending_key(seed: &[u8], coin_type: u32, account: u32) -> ExtendedSpendingKey {
+    ExtendedSpendingKey::from_path(
+        &ExtendedSpendingKey::master(&seed),
+        &[
+            ChildIndex::Hardened(32),
+            ChildIndex::Hardened(coin_type),
+            ChildIndex::Hardened(account),
+        ],
+    )
+}

zcash_client_backend/src/lib.rs

@@ -3,10 +3,5 @@
 //! `zcash_client_backend` contains Rust structs and traits for creating shielded Zcash
 //! light clients.
 
-#[cfg(test)]
+pub mod constants;
-mod tests {
+pub mod keys;
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}