Initial Rust implementation

Cargo.toml

@@ -15,6 +15,7 @@ include = [
     "/README.md",
     "build.rs",
     "src/*.rs",
+    "src/*/*.rs",
     "/depend/check_uint128_t.c",
     "/depend/zcash/src/amount.cpp",
     "/depend/zcash/src/amount.h",
@@ -62,6 +63,7 @@ rust-interpreter = []
 
 [dependencies]
 bitflags = "2.5"
+log = "0.4"
 
 [build-dependencies]
 # The `bindgen` dependency should automatically upgrade to match the version used by zebra-state's `rocksdb` dependency in:

src/external/mod.rs

@@ -0,0 +1,4 @@
+//! Modules that we use from Zcash, but that are outside the script directory.
+
+pub mod pubkey;
+pub mod uint256;

src/external/pubkey.rs

@@ -0,0 +1,23 @@
+use super::uint256::*;
+
+/// FIXME: `PUBLIC_KEY_SIZE` is meant to be an upper bound, it seems. Maybe parameterize the type
+///        over the size.
+pub struct PubKey<'a>(pub &'a [u8]);
+
+impl PubKey<'_> {
+    pub const PUBLIC_KEY_SIZE: usize = 65;
+    pub const COMPRESSED_PUBLIC_KEY_SIZE: usize = 33;
+
+    /// Check syntactic correctness.
+    ///
+    /// Note that this is consensus critical as CheckSig() calls it!
+    pub fn is_valid(&self) -> bool {
+        self.0.len() > 0
+    }
+
+    /// Verify a DER signature (~72 bytes).
+    /// If this public key is not fully valid, the return value will be false.
+    pub fn verify(&self, hash: &UInt256, vch_sig: &[u8]) -> bool {
+        todo!()
+    }
+}

src/external/uint256.rs

@@ -0,0 +1,2 @@
+/// FIXME: This probably needs to be an actually separate type somewhere.
+pub type UInt256 = [u8; 32];