From 8db848139b5fdfb8f216cae71bb38511b7f5afbb Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Wed, 11 Jul 2018 01:26:07 +0100
Subject: [PATCH] Basic conversions

---
 Cargo.toml |  1 +
 src/lib.rs | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 67 insertions(+), 1 deletion(-)

diff --git a/Cargo.toml b/Cargo.toml
index f97aee5..0872467 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,6 +12,7 @@ homepage = "https://github.com/zcash-hackworks/zip32"
 repository = "https://github.com/zcash-hackworks/zip32"
 
 [dependencies]
+lazy_static = "1.0"
 pairing = "0.14.2"
 
 [dependencies.sapling-crypto]
diff --git a/src/lib.rs b/src/lib.rs
index e696dd3..60429eb 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,12 +1,21 @@
+#[macro_use]
+extern crate lazy_static;
 extern crate pairing;
 extern crate sapling_crypto;
 
 use pairing::bls12_381::Bls12;
-use sapling_crypto::{jubjub::JubjubEngine, primitives::ViewingKey};
+use sapling_crypto::{
+    jubjub::{FixedGenerators, JubjubBls12, JubjubEngine, JubjubParams}, primitives::ViewingKey,
+};
+
+lazy_static! {
+    static ref JUBJUB: JubjubBls12 = { JubjubBls12::new() };
+}
 
 // Sapling key components
 
 /// An outgoing viewing key
+#[derive(Clone, Copy)]
 struct OutgoingViewingKey([u8; 32]);
 
 /// A Sapling expanded spending key
@@ -22,24 +31,67 @@ struct FullViewingKey<E: JubjubEngine> {
     ovk: OutgoingViewingKey,
 }
 
+impl<E: JubjubEngine> FullViewingKey<E> {
+    fn from_expanded_spending_key(xsk: &ExpandedSpendingKey<E>, params: &E::Params) -> Self {
+        FullViewingKey {
+            vk: ViewingKey {
+                ak: params
+                    .generator(FixedGenerators::SpendingKeyGenerator)
+                    .mul(xsk.ask, params),
+                nk: params
+                    .generator(FixedGenerators::ProofGenerationKey)
+                    .mul(xsk.nsk, params),
+            },
+            ovk: xsk.ovk,
+        }
+    }
+}
+
 // ZIP 32 structures
 
 /// A Sapling full viewing key fingerprint
 struct FVKFingerprint([u8; 32]);
 
 /// A Sapling full viewing key tag
+#[derive(Clone, Copy)]
 struct FVKTag([u8; 4]);
 
+impl<'a> From<&'a FVKFingerprint> for FVKTag {
+    fn from(fingerprint: &FVKFingerprint) -> Self {
+        let mut tag = [0u8; 4];
+        tag.copy_from_slice(&fingerprint.0[..4]);
+        FVKTag(tag)
+    }
+}
+
+impl From<FVKFingerprint> for FVKTag {
+    fn from(fingerprint: FVKFingerprint) -> Self {
+        (&fingerprint).into()
+    }
+}
+
 /// A child index for a derived key
+#[derive(Clone, Copy)]
 pub enum ChildIndex {
     NonHardened(u32),
     Hardened(u32), // Hardened(n) == n + (1 << 31) == n' in path notation
 }
 
+impl ChildIndex {
+    pub fn from_index(i: u32) -> Self {
+        match i {
+            n if n >= (1 << 31) => ChildIndex::Hardened(n - (1 << 31)),
+            n => ChildIndex::NonHardened(n),
+        }
+    }
+}
+
 /// A chain code
+#[derive(Clone, Copy)]
 struct ChainCode([u8; 32]);
 
 /// A key used to derive diversifiers for a particular child key
+#[derive(Clone, Copy)]
 struct DiversifierKey([u8; 32]);
 
 /// A Sapling extended spending key
@@ -62,6 +114,19 @@ pub struct ExtendedFullViewingKey {
     dk: DiversifierKey,
 }
 
+impl<'a> From<&'a ExtendedSpendingKey> for ExtendedFullViewingKey {
+    fn from(xsk: &ExtendedSpendingKey) -> Self {
+        ExtendedFullViewingKey {
+            depth: xsk.depth,
+            parent_fvk_tag: xsk.parent_fvk_tag,
+            child_index: xsk.child_index,
+            chain_code: xsk.chain_code,
+            fvk: FullViewingKey::from_expanded_spending_key(&xsk.xsk, &JUBJUB),
+            dk: xsk.dk,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     #[test]