Refactor NodeKeyFactory to improve key derivation logic

- Updated the `NodeKeyFactory` to use a constant for the uncompressed public key prefix length, enhancing code readability and maintainability.
- Adjusted the logic for deriving the `enode` to utilize the new constant, ensuring consistency across the implementation.
- Modified tests in `node-key-factory.test.ts` to reflect the changes in the key derivation process and validate the correct behavior of the `enode` field.

This refactor aims to streamline the key generation process and improve the clarity of the codebase.

Author: roderik

src/keys/node-key-factory.test.ts

@@ -4,6 +4,16 @@ import { NodeKeyFactory } from "./node-key-factory.ts";
 
 const factory = new NodeKeyFactory();
 
+/**
+ * Offset to skip the 0x04 uncompressed public key prefix when deriving the node ID.
+ */
+const UNCOMPRESSED_PUBLIC_KEY_PREFIX_LENGTH = 4;
+
+/**
+ * Expected length of a hex-encoded 64-byte node ID (128 hex characters).
+ */
+const NODE_ID_HEX_LENGTH = 128;
+
 describe("NodeKeyFactory", () => {
   test("generates unique key material", () => {
     const first = factory.generate();
@@ -14,9 +24,11 @@ describe("NodeKeyFactory", () => {
     expect(first.address.startsWith("0x")).toBe(true);
 
     // enode should be the node ID (public key with 0x04 prefix stripped)
-    expect(first.enode).toBe(first.publicKey.slice(4));
+    expect(first.enode).toBe(
+      first.publicKey.slice(UNCOMPRESSED_PUBLIC_KEY_PREFIX_LENGTH)
+    );
     expect(first.enode).not.toContain("0x");
-    expect(first.enode.length).toBe(128); // 64 bytes hex-encoded
+    expect(first.enode.length).toBe(NODE_ID_HEX_LENGTH);
 
     expect(first.privateKey).not.toBe(second.privateKey);
     expect(first.publicKey).not.toBe(second.publicKey);

src/keys/node-key-factory.ts

@@ -8,6 +8,16 @@ export type GeneratedNodeKey = {
   publicKey: Hex;
 };
 
+/**
+ * Offset to skip the 0x04 uncompressed public key prefix when deriving the node ID.
+ */
+const UNCOMPRESSED_PUBLIC_KEY_PREFIX_LENGTH = 4;
+
+/**
+ * Offset to skip the 0x hex prefix.
+ */
+const HEX_PREFIX_LENGTH = 2;
+
 /**
  * Provides lightweight wrappers around viem's account generation helpers.
  */
@@ -29,8 +39,8 @@ export class NodeKeyFactory {
     const address = account.address;
     // Derive node ID by stripping the 0x04 prefix from the uncompressed public key
     const enode = publicKey.startsWith("0x04")
-      ? publicKey.slice(4)
-      : publicKey.slice(2);
+      ? publicKey.slice(UNCOMPRESSED_PUBLIC_KEY_PREFIX_LENGTH)
+      : publicKey.slice(HEX_PREFIX_LENGTH);
 
     return {
       address,