Add PrfExpand domain for ZIP 32 arbitrary key derivation

CHANGELOG.md

@@ -7,6 +7,10 @@ and this library adheres to Rust's notion of
 
 ## [Unreleased]
 
+## [0.1.2] - 2024-10-01
+### Added
+- `zcash_spec::PrfExpand::ARBITRARY_ZIP32_CHILD`
+
 ## [0.1.1] - 2024-09-20
 ### Fixed
 - The `std` default feature of `blake2b_simd` is now disabled, to enable no-std

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "zcash_spec"
-version = "0.1.1"
+version = "0.1.2"
 authors = [
     "Jack Grigg <[email protected]>",
 ]

src/prf_expand.rs

@@ -95,6 +95,7 @@ with_inputs!(a, A);
 impl PrfExpand<([u8; 32], [u8; 4])> {
     pub const SPROUT_ZIP32_CHILD: Self = Self::new(0x80);
     pub const ORCHARD_ZIP32_CHILD: Self = Self::new(0x81);
+    pub const ARBITRARY_ZIP32_CHILD: Self = Self::new(0xAB);
 }
 impl PrfExpand<([u8; 32], [u8; 32])> {
     pub const ORCHARD_DK_OVK: Self = Self::new(0x82);