diff --git a/src/cli.ts b/src/cli.ts
index 42b20f5..23d5c84 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -118,11 +118,13 @@ async function cmdInstall(args: string[]): Promise<void> {
     ...(token ? { token } : {}),
   };
   await fsp.writeFile(agentConfigPath, JSON.stringify(agentConfig, null, 2) + '\n', 'utf-8');
+  await fsp.chmod(agentConfigPath, 0o600);
   console.log(`  Agent config: ${agentConfigPath}`);
 
   // Write private key (chmod 600)
   const keyPath = path.join(agentsDir, `${agentName}.key`);
   await fsp.writeFile(keyPath, privateKey, { encoding: 'utf-8', mode: 0o600 });
+  await fsp.chmod(keyPath, 0o600);
   console.log(`  Private key:  ${keyPath}`);
 
   // Generate and write hook script (PostToolUse — audit logging)
diff --git a/src/crypto.ts b/src/crypto.ts
index d2a3e20..3fa7422 100644
--- a/src/crypto.ts
+++ b/src/crypto.ts
@@ -151,8 +151,7 @@ export function derivePublicKey(privateKeyBase64url: string): string {
 // ---------------------------------------------------------------------------
 
 /**
- * The initial chain hash value: SHA-256 of 32 zero bytes, base64url encoded.
+ * The initial chain hash value: base64url encoding of 32 zero bytes.
+ * Must match the backend's GENESIS_CHAIN_HASH constant exactly.
  */
-export const ZERO_CHAIN_HASH: string = base64urlEncode(
-  crypto.createHash('sha256').update(Buffer.alloc(32, 0)).digest(),
-);
+export const ZERO_CHAIN_HASH: string = base64urlEncode(Buffer.alloc(32, 0));