Allow SpendValidatingKey to be constructed from bytes

closes #427

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to Rust's notion of
 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### changed
+- changed `SpendValidatingKey` serialization and deserialization from bytes
+visibility from `pub(crate)` to `pub`
+  - `orchard::keys::SpendValidatingKey`
 
 ## [0.8.0] - 2024-03-25
 

src/keys.rs

@@ -186,13 +186,16 @@ impl SpendValidatingKey {
 
     /// Converts this spend validating key to its serialized form,
     /// I2LEOSP_256(ak).
-    pub(crate) fn to_bytes(&self) -> [u8; 32] {
+    pub fn to_bytes(&self) -> [u8; 32] {
         // This is correct because the wrapped point must have ỹ = 0, and
         // so the point repr is the same as I2LEOSP of its x-coordinate.
         <[u8; 32]>::from(&self.0)
     }
 
-    pub(crate) fn from_bytes(bytes: &[u8]) -> Option<Self> {
+    /// Attempts to convert these bytes into a spend validating key
+    /// from its serialized form, I2LEOSP_256(ak). Returns None if
+    /// it can't be created.
+    pub fn from_bytes(bytes: &[u8]) -> Option<Self> {
         <[u8; 32]>::try_from(bytes)
             .ok()
             .and_then(|b| {