add auth paths

nssa/src/merkle_tree.rs

@@ -34,14 +34,13 @@ impl MerkleTree {
     }
 
     fn root_index(&self) -> usize {
-        let total_levels = self.capacity.trailing_zeros() as usize;
-        let used_levels = self.size().trailing_zeros() as usize;
-        let diff = total_levels - used_levels;
+        let capacity_depth = self.capacity.trailing_zeros() as usize;
+        let diff = capacity_depth - self.depth();
         if diff == 0 { 0 } else { (1 << diff) - 1 }
     }
 
-    fn size(&self) -> usize {
-        self.values.len().next_power_of_two()
+    fn depth(&self) -> usize {
+        self.values.len().next_power_of_two().trailing_zeros() as usize
     }
 
     fn get_node(&self, index: &usize) -> &Node {
@@ -71,7 +70,7 @@ impl MerkleTree {
         }
     }
 
-    fn extend_capacity(&mut self) {
+    fn reallocate_to_double_capacity(&mut self) {
         let mut this = Self::with_capacity(self.capacity << 1);
         for value in self.values.iter() {
             this.insert(*value);
@@ -85,7 +84,7 @@ impl MerkleTree {
         }
 
         if self.capacity == self.values.len() {
-            self.extend_capacity();
+            self.reallocate_to_double_capacity();
         }
 
         let new_index = self.values.len();
@@ -98,7 +97,7 @@ impl MerkleTree {
         self.node_map.insert(layer_index, layer_node);
 
         let mut layer = 0;
-        let mut top_layer = self.size().trailing_zeros();
+        let mut top_layer = self.depth();
         while layer < top_layer {
             let is_left_child = layer_index & 1 == 1;
 
@@ -139,6 +138,28 @@ impl MerkleTree {
         }
         this
     }
+
+    pub fn get_authentication_path_for(&self, value: &Value) -> Option<(usize, Vec<Node>)> {
+        let mut result = Vec::with_capacity(self.depth());
+        let value_index = self.index_map.get(value)?;
+        let base_length = self.capacity;
+        let mut layer_index = base_length + value_index - 1;
+        let mut layer = 0;
+        let top_layer = self.depth();
+        while layer < top_layer {
+            let is_left_child = layer_index & 1 == 1;
+            let (sibling, parent_index) = if is_left_child {
+                (self.get_node(&(layer_index + 1)), (layer_index - 1) >> 1)
+            } else {
+                (self.get_node(&(layer_index - 1)), (layer_index - 2) >> 1)
+            };
+            result.push(*sibling);
+
+            layer += 1;
+            layer_index = parent_index;
+        }
+        Some((*value_index, result))
+    }
 }
 
 #[cfg(test)]
@@ -245,6 +266,18 @@ mod tests {
         assert_eq!(tree.capacity, 8);
     }
 
+    #[test]
+    fn test_merkle_tree_6() {
+        let values = vec![[1; 32], [2; 32], [3; 32], [4; 32], [5; 32]];
+        let tree = MerkleTree::new(values);
+        let expected_root = [
+            6, 156, 184, 37, 154, 6, 254, 110, 219, 63, 167, 255, 121, 51, 166, 221, 125, 202, 111,
+            202, 41, 147, 20, 55, 151, 148, 166, 136, 146, 108, 55, 146,
+        ];
+
+        assert_eq!(tree.root(), expected_root);
+    }
+
     #[test]
     fn test_with_capacity_4() {
         let tree = MerkleTree::with_capacity(4);
@@ -381,6 +414,76 @@ mod tests {
 
         assert_eq!(expected_tree, tree);
     }
+
+    #[test]
+    fn test_authentication_path_1() {
+        let values = vec![[1; 32], [2; 32], [3; 32], [4; 32]];
+        let tree = MerkleTree::new(values);
+        let expected_authentication_path = (
+            2,
+            vec![
+                [
+                    159, 79, 182, 143, 62, 29, 172, 130, 32, 47, 154, 165, 129, 206, 11, 191, 31,
+                    118, 93, 240, 233, 172, 60, 140, 87, 226, 15, 104, 90, 186, 184, 237,
+                ],
+                [
+                    80, 162, 125, 71, 70, 243, 87, 203, 112, 12, 190, 157, 72, 131, 183, 127, 182,
+                    79, 1, 40, 130, 138, 52, 137, 220, 106, 111, 33, 221, 191, 36, 20,
+                ],
+            ],
+        );
+
+        let authentication_path = tree.get_authentication_path_for(&[3; 32]).unwrap();
+        assert_eq!(authentication_path, expected_authentication_path);
+    }
+
+    #[test]
+    fn test_authentication_path_2() {
+        let values = vec![[1; 32], [2; 32], [3; 32]];
+        let tree = MerkleTree::new(values);
+        let expected_authentication_path = (
+            0,
+            vec![
+                [
+                    117, 135, 123, 180, 29, 57, 59, 95, 184, 69, 92, 230, 14, 205, 141, 218, 0, 29,
+                    6, 49, 100, 150, 177, 77, 250, 127, 137, 86, 86, 238, 202, 74,
+                ],
+                [
+                    164, 27, 133, 93, 45, 180, 222, 144, 82, 205, 123, 229, 236, 103, 214, 88, 102,
+                    41, 203, 159, 110, 50, 70, 164, 175, 165, 186, 49, 63, 7, 169, 197,
+                ],
+            ],
+        );
+
+        let authentication_path = tree.get_authentication_path_for(&[1; 32]).unwrap();
+        assert_eq!(authentication_path, expected_authentication_path);
+    }
+
+    #[test]
+    fn test_authentication_path_3() {
+        let values = vec![[1; 32], [2; 32], [3; 32], [4; 32], [5; 32]];
+        let tree = MerkleTree::new(values);
+        let expected_authentication_path = (
+            4,
+            vec![
+                [
+                    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+                    0, 0, 0, 0, 0, 0,
+                ],
+                [
+                    245, 165, 253, 66, 209, 106, 32, 48, 39, 152, 239, 110, 211, 9, 151, 155, 67,
+                    0, 61, 35, 32, 217, 240, 232, 234, 152, 49, 169, 39, 89, 251, 75,
+                ],
+                [
+                    72, 199, 63, 120, 33, 165, 138, 141, 42, 112, 62, 91, 57, 197, 113, 192, 170,
+                    32, 207, 20, 171, 205, 10, 248, 242, 185, 85, 188, 32, 41, 152, 222,
+                ],
+            ],
+        );
+
+        let authentication_path = tree.get_authentication_path_for(&[5; 32]).unwrap();
+        assert_eq!(authentication_path, expected_authentication_path);
+    }
 }
 
 mod default_values {