Implement equihash verification (#549)

This change brings in the `equihash` crate from librustzcash and uses it to add a basic `is_valid` test for `EquihashSolutions`.

Co-authored-by: Jane Lusby <jane@zfnd.org>

Cargo.lock

@@ -428,6 +428,16 @@ dependencies = [
  "thiserror",
 ]
 
+[[package]]
+name = "equihash"
+version = "0.0.0"
+source = "git+https://github.com/ZcashFoundation/librustzcash.git?branch=equihash-crate#5b2c71e112ade5488ba49bb16f50897d513702f8"
+dependencies = [
+ "blake2b_simd",
+ "byteorder",
+ "log",
+]
+
 [[package]]
 name = "eyre"
 version = "0.6.0"
@@ -2300,6 +2310,7 @@ dependencies = [
  "byteorder",
  "chrono",
  "ed25519-zebra",
+ "equihash",
  "futures",
  "hex",
  "jubjub",

zebra-chain/Cargo.toml

@@ -29,6 +29,7 @@ serde-big-array = "0.3.0"
 # ZF deps
 ed25519-zebra = "0.4"
 redjubjub = "0.1"
+equihash = { git = "https://github.com/ZcashFoundation/librustzcash.git", branch = "equihash-crate" }
 
 [dev-dependencies]
 proptest = "0.10"

zebra-chain/src/equihash_solution.rs

@@ -28,6 +28,15 @@ pub struct EquihashSolution(
     #[serde(with = "serde_helpers::BigArray")] pub [u8; EQUIHASH_SOLUTION_SIZE],
 );
 
+impl EquihashSolution {
+    /// Validate an equihash solution
+    pub fn is_valid(&self, input: &[u8], nonce: &[u8]) -> bool {
+        let n = 200;
+        let k = 9;
+        equihash::is_valid_solution(n, k, input, nonce, &self.0)
+    }
+}
+
 impl PartialEq<EquihashSolution> for EquihashSolution {
     fn eq(&self, other: &EquihashSolution) -> bool {
         self.0.as_ref() == other.0.as_ref()
@@ -117,7 +126,8 @@ mod tests {
 
     }
 
-    const EQUIHASH_SOLUTION_BLOCK_OFFSET: usize = 4 + 32 * 3 + 4 * 2 + 32;
+    const EQUIHASH_NONCE_BLOCK_OFFSET: usize = 4 + 32 * 3 + 4 * 2;
+    const EQUIHASH_SOLUTION_BLOCK_OFFSET: usize = EQUIHASH_NONCE_BLOCK_OFFSET + 32;
 
     #[test]
     fn equihash_solution_test_vector() {
@@ -134,6 +144,27 @@ mod tests {
         assert_eq!(solution_bytes, data.as_slice());
     }
 
+    #[test]
+    fn equihash_solution_test_vector_is_valid() {
+        let block = crate::block::Block::zcash_deserialize(
+            &zebra_test::vectors::BLOCK_MAINNET_415000_BYTES[..],
+        )
+        .expect("block test vector should deserialize");
+
+        let solution = block.header.solution;
+        let header_bytes =
+            &zebra_test::vectors::HEADER_MAINNET_415000_BYTES[..EQUIHASH_NONCE_BLOCK_OFFSET];
+
+        assert!(solution.is_valid(header_bytes, &block.header.nonce));
+
+        let heade_bytes =
+            &zebra_test::vectors::HEADER_MAINNET_415000_BYTES[..EQUIHASH_NONCE_BLOCK_OFFSET - 1];
+        let headerr_bytes =
+            &zebra_test::vectors::HEADER_MAINNET_415000_BYTES[..EQUIHASH_NONCE_BLOCK_OFFSET + 1];
+        assert!(!solution.is_valid(heade_bytes, &block.header.nonce));
+        assert!(!solution.is_valid(headerr_bytes, &block.header.nonce));
+    }
+
     static EQUIHASH_SIZE_TESTS: &[u64] = &[
         0,
         1,