From bc074d0386a1560cd923f6399a362739a2c9ca49 Mon Sep 17 00:00:00 2001
From: Rene Vergara <rene@vergara.network>
Date: Wed, 1 May 2024 14:24:18 -0500
Subject: [PATCH] Add transparent key derivation

---
 CHANGELOG.md                    |  1 +
 src/ZcashHaskell/Transparent.hs | 17 ++++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e315c8..cf7b6d7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Type for transaction creation errors
 - Types for Sapling circuit parameters
 - Function to create transaction
+- Function to derive distinct transparent spending keys
 
 ### Changed
 
diff --git a/src/ZcashHaskell/Transparent.hs b/src/ZcashHaskell/Transparent.hs
index afe09e3..878a7d8 100644
--- a/src/ZcashHaskell/Transparent.hs
+++ b/src/ZcashHaskell/Transparent.hs
@@ -101,7 +101,22 @@ genTransparentReceiver i scope xprvk = do
     ScriptAddress j -> return $ TransparentReceiver P2SH $ fromBinary j
     _anyOtherKind -> throwIO $ userError "Unsupported transparent address type"
 
--- } decode a Transparent Address in HRF and return a TransparentAddress object
+-- | Generate a transparent receiver
+genTransparentSecretKey ::
+     Int -- ^ The index of the address to be created
+  -> Scope -- ^ `External` for wallet addresses or `Internal` for change addresses
+  -> XPrvKey -- ^ The transparent private key
+  -> IO TransparentSpendingKey
+genTransparentSecretKey i scope xprvk = do
+  ioCtx <- createContext
+  let s =
+        case scope of
+          External -> 0
+          Internal -> 1
+  let path = Deriv :/ s :/ fromIntegral i :: DerivPath
+  return $ derivePath ioCtx path xprvk
+
+-- | decode a Transparent Address in HRF and return a TransparentAddress object
 decodeTransparentAddress :: BS.ByteString -> Maybe TransparentAddress
 decodeTransparentAddress taddress = do
   if BS.length taddress < 34