#129 Update SMT to use version 6a instead of 3o

Author: martti007

src/api/InclusionCertificate.ts

@@ -5,6 +5,7 @@ import { HashAlgorithm } from '../crypto/hash/HashAlgorithm.js';
 import { FinalizedBranch } from '../smt/radix/FinalizedBranch.js';
 import { FinalizedLeafBranch } from '../smt/radix/FinalizedLeafBranch.js';
 import { SparseMerkleTreeRootNode } from '../smt/radix/SparseMerkleTreeRootNode.js';
+import { pathToRegion } from '../smt/SparseMerkleTreePathUtils.js';
 import { BitString } from '../util/BitString.js';
 import { HexConverter } from '../util/HexConverter.js';
 import { dedent } from '../util/StringUtils.js';
@@ -145,6 +146,7 @@ export class InclusionCertificate {
 
       hash = await new DataHasher(HashAlgorithm.SHA256)
         .update(new Uint8Array([0x01, depth]))
+        .update(pathToRegion(keyPath, depth))
         .update(left)
         .update(right)
         .digest();

src/smt/SparseMerkleTreePathUtils.ts

@@ -1,19 +1,34 @@
-type CommonPath = { length: bigint; path: bigint };
+type CommonPath = { length: number; path: bigint };
 
 export function calculateCommonPath(path1: bigint, path2: bigint): CommonPath {
   let path = 1n;
   let mask = 1n;
-  let length = 0n;
+  let length = 0;
 
   while ((path1 & mask) === (path2 & mask) && path < path1 && path < path2) {
     mask <<= 1n;
-    length += 1n;
+    length += 1;
     path = mask | ((mask - 1n) & path1);
   }
 
   return { length, path };
 }
 
+/**
+ * Region committed by an interior node (v6a): the node's `depth`-bit key prefix, packed into 32
+ * bytes in the byte-order-preserving, LSB-in-byte convention. `path` is the absolute node/key path
+ * (leading sentinel bit at `depth`); its low `depth` bits are the prefix. Bit `i` lives in byte
+ * `⌊i/8⌋` least-significant-first, so the packing is little-endian.
+ */
+export function pathToRegion(path: bigint, depth: number): Uint8Array {
+  const bits = path & ((1n << BigInt(depth)) - 1n);
+  const region = new Uint8Array(32);
+  for (let j = 0; j * 8 < depth; j++) {
+    region[j] = Number((bits >> BigInt(8 * j)) & 0xffn);
+  }
+  return region;
+}
+
 export function getBitAtDepth(data: Uint8Array, depth: number): number {
   depth = Number(depth);
   const byteIndex = Math.floor(depth / 8);

src/smt/radix/FinalizedNodeBranch.ts

@@ -4,6 +4,7 @@ import { DataHash } from '../../crypto/hash/DataHash.js';
 import { IDataHasher } from '../../crypto/hash/IDataHasher.js';
 import { IDataHasherFactory } from '../../crypto/hash/IDataHasherFactory.js';
 import { dedent } from '../../util/StringUtils.js';
+import { pathToRegion } from '../SparseMerkleTreePathUtils.js';
 
 /**
  * Finalized interior node in a radix sparse Merkle tree.
@@ -32,6 +33,7 @@ export class FinalizedNodeBranch {
     const hash = await factory
       .create()
       .update(new Uint8Array([0x01, node.depth]))
+      .update(pathToRegion(node.path, node.depth))
       .update(left.hash.data)
       .update(right.hash.data)
       .digest();

src/smt/radix/SparseMerkleTree.ts

@@ -43,7 +43,7 @@ export class SparseMerkleTree {
     const isRight = Number(path & 1n);
     const branchPromise = isRight ? this.right : this.left;
     const newBranchPromise = branchPromise.then((branch) =>
-      branch ? this.buildTree(branch, path, 0, key, data) : new PendingLeafBranch(path, key, data),
+      branch ? this.buildTree(branch, path, key, data) : new PendingLeafBranch(path, key, data),
     );
 
     if (isRight) {
@@ -74,18 +74,11 @@ export class SparseMerkleTree {
     return SparseMerkleTreeRootNode.create(left, right, this.factory);
   }
 
-  private buildTree(
-    branch: PendingBranch,
-    remainingPath: bigint,
-    depth: number,
-    key: Uint8Array,
-    data: Uint8Array,
-  ): PendingBranch {
-    const commonPath = calculateCommonPath(remainingPath, branch.path);
-    const commonPathLength = Number(commonPath.length);
-    const isRight = Number((remainingPath >> commonPath.length) & 1n);
+  private buildTree(branch: PendingBranch, keyPath: bigint, key: Uint8Array, data: Uint8Array): PendingBranch {
+    const commonPath = calculateCommonPath(keyPath, branch.path);
+    const isRight = Number((keyPath >> BigInt(commonPath.length)) & 1n);
 
-    if (commonPath.path === remainingPath) {
+    if (commonPath.path === keyPath) {
       throw new LeafInBranchError();
     }
 
@@ -95,30 +88,23 @@ export class SparseMerkleTree {
         throw new LeafOutOfBoundsError();
       }
 
-      const oldBranch = new PendingLeafBranch(branch.path >> commonPath.length, branch.key, branch.data);
-      const newBranch = new PendingLeafBranch(remainingPath >> commonPath.length, key, data);
+      const newBranch = new PendingLeafBranch(keyPath, key, data);
       return new PendingNodeBranch(
         commonPath.path,
-        depth + commonPathLength,
-        isRight ? oldBranch : newBranch,
-        isRight ? newBranch : oldBranch,
+        commonPath.length,
+        isRight ? branch : newBranch,
+        isRight ? newBranch : branch,
       );
     }
 
     // If node branch is split in the middle
     if (commonPath.path < branch.path) {
-      const newBranch = new PendingLeafBranch(remainingPath >> commonPath.length, key, data);
-      const oldBranch = new PendingNodeBranch(
-        branch.path >> commonPath.length,
-        branch.depth,
-        branch.left,
-        branch.right,
-      );
+      const newBranch = new PendingLeafBranch(keyPath, key, data);
       return new PendingNodeBranch(
         commonPath.path,
-        depth + commonPathLength,
-        isRight ? oldBranch : newBranch,
-        isRight ? newBranch : oldBranch,
+        commonPath.length,
+        isRight ? branch : newBranch,
+        isRight ? newBranch : branch,
       );
     }
 
@@ -127,14 +113,14 @@ export class SparseMerkleTree {
         branch.path,
         branch.depth,
         branch.left,
-        this.buildTree(branch.right, remainingPath >> commonPath.length, depth + commonPathLength, key, data),
+        this.buildTree(branch.right, keyPath, key, data),
       );
     }
 
     return new PendingNodeBranch(
       branch.path,
       branch.depth,
-      this.buildTree(branch.left, remainingPath >> commonPath.length, depth + commonPathLength, key, data),
+      this.buildTree(branch.left, keyPath, key, data),
       branch.right,
     );
   }

src/smt/radixsum/SparseMerkleSumTree.ts

@@ -56,7 +56,7 @@ export class SparseMerkleSumTree {
     const isRight = Number(path & 1n);
     const branchPromise = isRight ? this.right : this.left;
     const newBranchPromise = branchPromise.then((branch) =>
-      branch ? this.buildTree(branch, path, 0, key, data, value) : new PendingLeafBranch(path, key, data, value),
+      branch ? this.buildTree(branch, path, key, data, value) : new PendingLeafBranch(path, key, data, value),
     );
 
     if (isRight) {
@@ -89,17 +89,15 @@ export class SparseMerkleSumTree {
 
   private buildTree(
     branch: PendingBranch,
-    remainingPath: bigint,
-    depth: number,
+    keyPath: bigint,
     key: Uint8Array,
     data: Uint8Array,
     value: bigint,
   ): PendingBranch {
-    const commonPath = calculateCommonPath(remainingPath, branch.path);
-    const commonPathLength = Number(commonPath.length);
-    const isRight = Number((remainingPath >> commonPath.length) & 1n);
+    const commonPath = calculateCommonPath(keyPath, branch.path);
+    const isRight = Number((keyPath >> BigInt(commonPath.length)) & 1n);
 
-    if (commonPath.path === remainingPath) {
+    if (commonPath.path === keyPath) {
       throw new LeafInBranchError();
     }
 
@@ -109,30 +107,23 @@ export class SparseMerkleSumTree {
         throw new LeafOutOfBoundsError();
       }
 
-      const oldBranch = new PendingLeafBranch(branch.path >> commonPath.length, branch.key, branch.data, branch.value);
-      const newBranch = new PendingLeafBranch(remainingPath >> commonPath.length, key, data, value);
+      const newBranch = new PendingLeafBranch(keyPath, key, data, value);
       return new PendingNodeBranch(
         commonPath.path,
-        depth + commonPathLength,
-        isRight ? oldBranch : newBranch,
-        isRight ? newBranch : oldBranch,
+        commonPath.length,
+        isRight ? branch : newBranch,
+        isRight ? newBranch : branch,
       );
     }
 
     // If node branch is split in the middle
     if (commonPath.path < branch.path) {
-      const newBranch = new PendingLeafBranch(remainingPath >> commonPath.length, key, data, value);
-      const oldBranch = new PendingNodeBranch(
-        branch.path >> commonPath.length,
-        branch.depth,
-        branch.left,
-        branch.right,
-      );
+      const newBranch = new PendingLeafBranch(keyPath, key, data, value);
       return new PendingNodeBranch(
         commonPath.path,
-        depth + commonPathLength,
-        isRight ? oldBranch : newBranch,
-        isRight ? newBranch : oldBranch,
+        commonPath.length,
+        isRight ? branch : newBranch,
+        isRight ? newBranch : branch,
       );
     }
 
@@ -141,14 +132,14 @@ export class SparseMerkleSumTree {
         branch.path,
         branch.depth,
         branch.left,
-        this.buildTree(branch.right, remainingPath >> commonPath.length, depth + commonPathLength, key, data, value),
+        this.buildTree(branch.right, keyPath, key, data, value),
       );
     }
 
     return new PendingNodeBranch(
       branch.path,
       branch.depth,
-      this.buildTree(branch.left, remainingPath >> commonPath.length, depth + commonPathLength, key, data, value),
+      this.buildTree(branch.left, keyPath, key, data, value),
       branch.right,
     );
   }

tests/unit/smt/SparseMerkleTreeUtilsTest.ts

@@ -2,10 +2,10 @@ import { calculateCommonPath } from '../../../src/smt/SparseMerkleTreePathUtils.
 
 describe('Sparse Merkle Tree tests', function () {
   it('calculate common path', () => {
-    expect(calculateCommonPath(0b11n, 0b111101111n)).toStrictEqual({ length: 1n, path: 0b11n });
-    expect(calculateCommonPath(0b111101111n, 0b11n)).toStrictEqual({ length: 1n, path: 0b11n });
+    expect(calculateCommonPath(0b11n, 0b111101111n)).toStrictEqual({ length: 1, path: 0b11n });
+    expect(calculateCommonPath(0b111101111n, 0b11n)).toStrictEqual({ length: 1, path: 0b11n });
     expect(calculateCommonPath(0b110010000n, 0b100010000n)).toStrictEqual({
-      length: 7n,
+      length: 7,
       path: 0b10010000n,
     });
   });

tests/unit/smt/radix/SparseMerkleTreeTest.ts

@@ -59,7 +59,7 @@ describe('Sparse Merkle Tree tests', function () {
     const root = await smt.calculateRoot();
 
     expect(root.hash.imprint).toStrictEqual(
-      HexConverter.decode('00000fbe49c19df8bbf8612951ea26c8b0c52088424ff48adacf56234fc567950e89'),
+      HexConverter.decode('0000cd23fc1265484a7173323cd862b85a61796b8e0af31149944a828e6c1734b846'),
     );
   });
 
@@ -103,6 +103,50 @@ describe('Sparse Merkle Tree tests', function () {
     expect(() => InclusionCertificate.create(emptyRoot, keys[0])).toThrow();
   });
 
+  it('empty and single-leaf roots', async () => {
+    const hashFactory = new DataHasherFactory(HashAlgorithm.SHA256, NodeDataHasher);
+
+    // Empty tree → all-zero root hash.
+    const emptyRoot = await new SparseMerkleTree(hashFactory).calculateRoot();
+    expect(emptyRoot.hash.data).toStrictEqual(new Uint8Array(32));
+
+    // Single leaf → root hash equals the leaf hash (no interior node, so no region involved).
+    const smt = new SparseMerkleTree(hashFactory);
+    const key = key32(0b10110010);
+    const value = new Uint8Array([9, 9, 9]);
+    await smt.addLeaf(key, value);
+    const root = await smt.calculateRoot();
+    const leaf = await new PendingLeafBranch(0n, key, value).finalize(hashFactory);
+    expect(root.hash.equals(leaf.hash)).toBe(true);
+  });
+
+  it('deep split at depth 255 verifies with region', async () => {
+    const hashFactory = new DataHasherFactory(HashAlgorithm.SHA256, NodeDataHasher);
+    const smt = new SparseMerkleTree(hashFactory);
+
+    // Two keys identical except bit 255 (high bit of the last byte) → a single interior node at depth 255.
+    const a = new Uint8Array(32);
+    const b = new Uint8Array(32);
+    b[31] = 0x80;
+    const valueA = new Uint8Array(32);
+    valueA[0] = 1;
+    const valueB = new Uint8Array(32);
+    valueB[0] = 2;
+    await smt.addLeaf(a, valueA);
+    await smt.addLeaf(b, valueB);
+    const root = await smt.calculateRoot();
+
+    for (const [key, value] of [
+      [a, valueA],
+      [b, valueB],
+    ] as const) {
+      const cert = InclusionCertificate.create(root, key);
+      const stateId = StateId.fromCBOR(CborSerializer.encodeByteString(key));
+      const leafValue = new DataHash(HashAlgorithm.SHA256, value);
+      await expect(cert.verify(stateId, leafValue, root.hash)).resolves.toBe(true);
+    }
+  });
+
   it('should handle concurrent addLeaf calls', async () => {
     const smt = new SparseMerkleTree(new DataHasherFactory(HashAlgorithm.SHA256, NodeDataHasher));
     const textEncoder = new TextEncoder();