SurgiSplit: Robotic Surgery Command Integrity

Executive Summary

Robotic surgery systems require cryptographic integrity for every command sent to the robot. A single compromised node, software bug, or network fault can issue a harmful command with irreversible consequences for patient safety.

SurgiSplit addresses this by splitting each surgical command via XorIDA threshold sharing across multiple independent verification nodes (surgeon console, anesthesiologist station, safety monitor). No single node can reconstruct and execute a command. A threshold of nodes must independently verify and agree before reconstruction is possible.

Each share is HMAC-SHA256 integrity-checked before reconstruction. Tampered shares are rejected immediately. The system provides defense-in-depth for safety-critical surgical operations with information-theoretic security — an attacker who compromises fewer than the threshold nodes learns nothing about the original command.

Zero npm runtime dependencies. Two core functions: splitCommand() and verifyAndReconstruct(). Production-ready with comprehensive error handling and audit trail support via SHA-256 command hashing.

The Problem

Modern robotic surgical systems like da Vinci send commands from a surgeon console to a patient-side robotic manipulator. These commands directly control surgical instruments performing delicate operations inside the human body. A single corrupted or malicious command can cause irreversible patient harm.

Single Point of Failure

Traditional robotic surgery architectures rely on a direct command path from surgeon console to robot. If the console is compromised — by malware, a software bug, a supply chain attack, or an adversarial actor — there is no independent verification layer. The robot executes whatever command it receives.

No Cryptographic Verification

Existing systems may use checksums or CRC validation to detect transmission errors, but these mechanisms do not provide cryptographic integrity. An attacker who compromises the command path can recalculate the checksum for a tampered command, and the robot will execute it without question.

Insider Threats & Coercion

Even with authentication, a single privileged operator (surgeon, surgical tech, or system administrator) can issue commands. Coercion, social engineering, or credential theft can bypass access controls. There is no K-of-N threshold requirement to prevent a single compromised node from acting unilaterally.

No Audit Trail

Post-operative forensic analysis requires a verifiable record of which commands were issued, when, and by whom. Without a cryptographic audit trail, command logs can be altered or deleted. There is no way to prove that the logged commands match the commands that were actually executed.

Solution

SurgiSplit splits each surgical command via XorIDA threshold sharing across multiple independent verification nodes. Reconstruction requires a threshold of nodes to agree. No single compromised node can issue or execute a command unilaterally.

How It Works

When the surgeon issues a command (e.g., "move instrument arm 2mm left"), SurgiSplit splits the command into N shares using XorIDA. Each share is assigned to a verification node:

• Surgeon Console: Receives share 1
• Anesthesiologist Station: Receives share 2
• Safety Monitor: Receives share 3

Each node independently verifies the command (checking timestamp, priority, procedure ID, etc.). If a node approves, it submits its share to the robot. When the robot receives K shares (the threshold), it reconstructs the original command, verifies HMAC integrity, and executes.

Information-Theoretic Security

An attacker who compromises fewer than K nodes learns nothing about the original command. This is not computational hardness — it is mathematical impossibility. Even a quantum computer cannot recover the command from K-1 shares. This property is unique to XorIDA threshold sharing over GF(2).

HMAC Integrity Verification

Each share includes an HMAC-SHA256 signature. Before reconstruction, the robot verifies every share's HMAC. A single tampered share causes immediate rejection. This prevents share substitution attacks and detects transmission corruption.

SHA-256 Audit Trail

Every split operation produces a SHA-256 hash of the original command. This hash is stored in the surgical audit log. Post-operative review can cryptographically verify that the reconstructed command matches the logged hash, providing a tamper-evident forensic record.

Use Cases

SurgiSplit applies to any safety-critical robotic surgery operation where command integrity and multi-party verification are required.

Architecture

SurgiSplit is a pure TypeScript library built on XorIDA threshold sharing from @private.me/crypto. Zero npm runtime dependencies. Runs anywhere Web Crypto API is available.

Core Components

Command Splitter

The splitCommand() function takes a SurgicalCommand and a SurgiConfig (list of verification nodes + threshold). It performs the following operations:

1. Validates configuration (threshold ≥ 2, threshold ≤ node count, unique node IDs)
2. Validates command (non-empty data, valid timestamp, priority level)
3. Splits the command data via XorIDA into N shares
4. Computes HMAC-SHA256 for each share
5. Computes SHA-256 hash of the original command for audit trail
6. Returns CommandSplitResult with shares + command hash

Command Verifier

The verifyAndReconstruct() function takes an array of CommandShare objects and reconstructs the original command. It performs:

1. Share validation (consistent command ID, total, threshold, no duplicates)
2. Threshold check (at least K shares provided)
3. HMAC-SHA256 verification for every share (fail-fast on first HMAC failure)
4. XorIDA reconstruction from K shares
5. Padding removal and size validation
6. Returns reconstructed command data as Uint8Array

Data Flow

1. Surgeon issues command via console UI
   ↓
2. SurgiSplit.splitCommand() creates 3 shares
   ↓
3. Each share sent to verification node (surgeon/anesth/monitor)
   ↓
4. Each node independently verifies command metadata
   ↓
5. Approved nodes submit shares to robot
   ↓
6. Robot receives K shares (threshold = 2)
   ↓
7. SurgiSplit.verifyAndReconstruct() validates HMAC + reconstructs
   ↓
8. Robot executes command
   ↓
9. Audit log records SHA-256 command hash + timestamp

API Reference

Installation

pnpm add @private.me/surgisplit

Core Functions

Usage Example

import { splitCommand, verifyAndReconstruct } from '@private.me/surgisplit';
import type { SurgicalCommand, SurgiConfig } from '@private.me/surgisplit';

// Define command
const command: SurgicalCommand = {
  commandId: 'cmd-001',
  procedureId: 'proc-2026-0042',
  robotId: 'davinci-xi-7',
  commandType: 'move',
  data: new Uint8Array([/* command bytes */]),
  timestamp: Date.now(),
  priority: 'critical',
};

// Define verification nodes
const config: SurgiConfig = {
  nodes: [
    { id: 'surgeon', name: 'Lead Surgeon Console', role: 'surgeon' },
    { id: 'anesth', name: 'Anesthesiologist Station', role: 'anesthesiologist' },
    { id: 'monitor', name: 'Safety Monitor', role: 'safety' },
  ],
  threshold: 2,
};

// Split command
const splitResult = await splitCommand(command, config);
if (!splitResult.ok) {
  console.error('Split failed:', splitResult.error.message);
  return;
}

// Distribute shares to verification nodes...
// Each node verifies and submits to robot...
// Robot collects shares and reconstructs...

// Reconstruct command (robot side)
const reconstructed = await verifyAndReconstruct(splitResult.value.shares);
if (!reconstructed.ok) {
  console.error('Reconstruction failed:', reconstructed.error.message);
  return;
}

// Execute command
console.log('Command reconstructed successfully');
executeRobotCommand(reconstructed.value);

Integration

SurgiSplit integrates with existing robotic surgery systems as a command integrity layer. It does not replace the robot's control system — it adds threshold verification before command execution.

Integration Pattern

Insert SurgiSplit between the surgeon console and the robot controller:

1. Console Integration: Modify surgeon console software to call splitCommand() instead of sending raw commands directly to the robot
2. Node Distribution: Route each share to its assigned verification node via secure network channels
3. Node Verification UI: Each verification node displays command metadata (type, timestamp, priority) and prompts operator for approval
4. Share Submission: Approved nodes submit shares to robot via authenticated API
5. Robot Reconstruction: Robot controller buffers shares until threshold is met, then calls verifyAndReconstruct()
6. Execution: Robot executes reconstructed command only after HMAC verification passes

Network Transport

Shares can be transmitted via any reliable transport (WebSocket, MQTT, custom UDP protocol). SurgiSplit is transport-agnostic. Each share is Base64-encoded for easy serialization.

Audit Logging

Store the commandHash from CommandSplitResult in the surgical audit log along with timestamp, operator ID, and procedure ID. Post-operative verification can confirm that the logged hash matches the executed command.

Security

Information-Theoretic Security

XorIDA threshold sharing over GF(2) provides unconditional security. Any subset of shares below the threshold reveals zero information about the original command. This is not computational hardness — it is mathematical impossibility. A quantum computer with infinite compute power cannot recover the command from K-1 shares.

HMAC-SHA256 Integrity

Every share includes an HMAC-SHA256 signature computed from a secret key. Before reconstruction, verifyAndReconstruct() verifies every share's HMAC. A single tampered share causes immediate rejection with error code HMAC_FAILURE. This prevents:

• Share substitution attacks
• Man-in-the-middle modification
• Transmission corruption
• Replay attacks (HMAC includes share index + timestamp)

No Math.random()

All random bytes for padding and HMAC keys are generated via crypto.getRandomValues() (Web Crypto API). Never Math.random(). This ensures cryptographic-quality randomness on all platforms.

Fail-Closed Behavior

If reconstruction fails for any reason (HMAC failure, insufficient shares, invalid padding), the system rejects the command and does not execute. There is no fallback to legacy unverified execution. This fail-closed behavior is critical for safety-critical systems.

Audit Trail Integrity

The SHA-256 command hash provides tamper-evident audit logs. Post-operative review can verify that the logged hash matches the reconstructed command. If hashes do not match, the audit log has been tampered with or the wrong command was executed.

Benchmarks

All benchmarks measured on Node.js 20.11.0, Apple M1 Pro (8P+2E cores), macOS 14.3. Operations are CPU-bound and single-threaded.

Latency Analysis

Typical surgical robot commands are small (64-512 bytes: joint angles, velocities, force limits). SurgiSplit adds <1ms overhead for split + reconstruct. Network transmission time dominates end-to-end latency.

Throughput

Robotic surgery systems typically issue 50-200 commands per second during active manipulation. SurgiSplit can process 1,000+ split operations per second on modern hardware, far exceeding surgical command rates.

Honest Limitations

SurgiSplit is not a complete robotic surgery security solution. It solves command integrity, not authentication, network security, or physical robot security.

Key Distribution

SurgiSplit requires a shared HMAC secret key across all nodes. This key must be securely provisioned during system setup. Key distribution is outside the scope of this package. Consider using HSM-backed key ceremony, hardware tokens, or a secure enclave for key provisioning.

Network Security

Shares transmitted over the network should be encrypted via TLS/DTLS. SurgiSplit does not encrypt shares in transit — it only provides HMAC integrity. Network eavesdropping can observe shares, but cannot reconstruct the command without the threshold.

Node Authentication

SurgiSplit does not authenticate verification nodes. The integration layer must ensure that only authorized nodes can submit shares to the robot. Use mutual TLS, API keys, or DID-based authentication (via Xlink) to authenticate nodes.

Physical Robot Security

SurgiSplit cannot prevent physical tampering with the robot hardware. If an attacker gains physical access to the robot controller and extracts the HMAC key from memory, they can forge shares. Physical security controls (locked server rooms, tamper-evident seals) are required.

Operator Collusion

If K operators collude, they can issue arbitrary commands. SurgiSplit does not prevent collusion — it only prevents unilateral action. Choose the threshold K to balance usability and security. Higher K reduces collusion risk but increases operational friction.

Denial of Service

A single malicious verification node can refuse to submit its share, preventing command execution. This is by design (fail-closed behavior). The system prioritizes safety over availability. If a node is suspected of malicious behavior, it must be removed from the configuration.

Error Code Reference

SurgiSplit uses structured error codes with Result<T, E> pattern. Every error includes a machine-readable code and human-readable message.

Error Handling Example

const result = await verifyAndReconstruct(shares);

if (!result.ok) {
  switch (result.error.code) {
    case 'HMAC_FAILURE':
      // Share tampering detected - abort operation
      logger.error('SECURITY ALERT: Share tampering detected');
      notifySecurityTeam(result.error);
      break;

    case 'INSUFFICIENT_SHARES':
      // Not enough nodes approved - wait for more
      logger.warn('Waiting for additional verification nodes');
      break;

    default:
      logger.error(`Reconstruction error: ${result.error.message}`);
  }
  return;
}

Multi-Party Verification Flow

Production surgical systems require careful choreography of verification nodes to balance security, usability, and fault tolerance.

Verification Node Roles

Threshold Selection Guidelines

2-of-3: Standard for most procedures. Surgeon + one other approver. Tolerates one node failure. Low operational friction.

2-of-4: Higher fault tolerance. Tolerates two node failures. Recommended for long procedures (>4 hours).

3-of-4: High-risk procedures (neurosurgery, cardiac). Requires majority approval. Lower fault tolerance but stronger security.

Emergency Override

In true emergency situations (patient hemorrhaging, airway obstruction), waiting for multi-party approval may be unsafe. Consider a separate emergency command path with post-hoc audit logging and mandatory review. Emergency commands should be logged with higher severity and trigger automatic incident investigation.