MCPS -- MCP Secure

The HTTPS of the agent era. Cryptographic identity, message signing, and trust verification for the Model Context Protocol.

Try it live in your browser -- no install needed

Generate keys, create passports, sign messages, verify signatures, and test tamper detection -- all client-side using Web Crypto API.

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The Problem

MCP has no identity layer. Any agent can call any tool. No signatures. No revocation. No tamper detection.

Real CVEs exist (CVSS 9.6). OWASP created an entire Top 10 for MCP risks. 82% of MCP servers have path traversal vulnerabilities.

MCP is HTTP. MCPS is HTTPS.

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How It Works

Agent                          MCP Server
  |                                |
  |-- 1. Generate ECDSA keys ----> |
  |-- 2. Create passport --------> |
  |                                |
  |== Signed JSON-RPC envelope ===>|
  |   {                            |
  |     mcps: {                    |
  |       version: "1.0",          |  3. Verify signature
  |       passport_id: "asp_...",  |  4. Check passport not revoked
  |       nonce: "abc123",         |  5. Reject if replayed
  |       timestamp: "2026-...",   |  6. Check trust level >= min
  |       signature: "base64..."   |
  |     },                         |
  |     jsonrpc: "2.0",            |
  |     method: "tools/call",      |
  |     params: { ... }            |
  |   }                            |
  |                                |
  |<====== Signed response ========|

Every message is wrapped in a signed envelope. Tamper any field -- the signature breaks. Replay a message -- the nonce is rejected. Revoke an agent -- instant cutoff.

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Try It in 30 Seconds

npm install mcp-secure

const mcps = require('mcp-secure');

// 1. Generate keys (ECDSA P-256)
const keys = mcps.generateKeyPair();

// 2. Create a passport for your agent
const passport = mcps.createPassport({
  name: 'my-agent',
  version: '1.0.0',
  publicKey: keys.publicKey,
});

// 3. Sign an MCP message
const envelope = mcps.signMessage(
  { jsonrpc: '2.0', method: 'tools/call', params: { name: 'read_file' } },
  passport.passport_id,
  keys.privateKey
);

// 4. Verify on the receiving end
const result = mcps.verifyMessage(envelope, keys.publicKey);
console.log(result.valid); // true

// 5. Tamper detection -- change anything, signature breaks
envelope.params.name = 'delete_everything';
const tampered = mcps.verifyMessage(envelope, keys.publicKey);
console.log(tampered.valid); // false

Python:

pip install mcp-secure

from mcp_secure import generate_key_pair, create_passport, sign_message, verify_message

keys = generate_key_pair()
passport = create_passport(name="my-agent", version="1.0.0", public_key=keys["public_key"])
envelope = sign_message({"jsonrpc": "2.0", "method": "tools/call"}, passport["passport_id"], keys["private_key"])
result = verify_message(envelope, keys["public_key"])
assert result["valid"] is True

Interactive playground: agentsign.dev/playground -- try it in the browser, no install needed.

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Wrap Any MCP Server (2 Lines)

const { secureMCP } = require('mcp-secure');

const server = secureMCP(myMCPServer, {
  passport: 'asp_abc123',
  privateKey: process.env.MCPS_PRIVATE_KEY,
  trustAuthority: 'https://agentsign.dev',
  minTrustLevel: 2,
});

Every incoming MCP call is now verified: passport checked, signature validated, replay blocked, audit logged.

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What MCPS Adds

Feature	What It Does
Agent Passports	ECDSA P-256 signed identity credentials -- agents carry proof of who they are
Message Signing	Every JSON-RPC message wrapped in a signed envelope with nonce + timestamp
Tool Integrity	Signed tool definitions prevent poisoning and rug pulls
Transcript Binding	Anti-downgrade binding -- cryptographically binds handshake parameters to prevent capability stripping
Replay Protection	Nonce + 5-minute timestamp window blocks replay attacks
Revocation	Real-time passport revocation via Trust Authority
Trust Levels	L0 (unsigned) through L4 (audited) -- progressive security
Version Negotiation	Client and server agree on protocol version at handshake
Issuer Chains	Delegated trust -- Trust Authority signs a passport, that passport signs sub-agents

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Trust Levels

L0  Unsigned     Plain MCP, no MCPS
L1  Identified   Passport presented
L2  Verified     Passport verified + not revoked
L3  Scanned      Verified + passed OWASP security scan
L4  Audited      Scanned + manual audit by Trust Authority

Use minTrustLevel to set the floor. An L2 server rejects L0/L1 agents. An L4 server only accepts fully audited agents.

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Tool Integrity (Prevents Tool Poisoning)

// Author signs their tool definition
const sig = mcps.signTool(myTool, authorPrivateKey);

// Client verifies before calling -- detects tampering
const safe = mcps.verifyTool(myTool, sig, authorPublicKey);
// If someone changed the tool description (tool poisoning), this returns false

Tool poisoning is MCP03 in the OWASP Top 10. This is the fix.

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Transcript Binding (Anti-Downgrade)

// Both sides sign the agreed security parameters after handshake
const binding = mcps.createTranscriptBinding(clientInitParams, serverInitResult, keys.privateKey);

// Verify the other party's binding -- detects capability stripping attacks
const result = mcps.verifyTranscriptBinding(
  binding.transcript_hash, binding.transcript_signature,
  keys.publicKey, clientInitParams, serverInitResult
);
console.log(result.valid); // true

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OWASP MCP Top 10 Coverage

MCPS mitigates 8 of 10 OWASP MCP risks:

OWASP Risk	MCPS Mitigation
MCP01: Token Mismanagement	Passport-based identity replaces long-lived tokens
MCP03: Tool Poisoning	Tool integrity signatures
MCP04: Supply Chain	Signed tool definitions + scan results in passport
MCP06: Intent Flow Subversion	Signed messages prevent manipulation
MCP07: Insufficient Auth	Passport verification on every connection
MCP08: Lack of Audit	Signed audit trail with every call
MCP09: Shadow Servers	Only passported agents accepted
MCP10: Context Injection	Envelope isolation prevents cross-session leakage

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Error Codes

Code	Meaning
MCPS-001	Invalid passport format
MCPS-002	Passport expired
MCPS-003	Passport revoked
MCPS-004	Invalid message signature
MCPS-005	Replay attack detected
MCPS-006	Timestamp out of window
MCPS-007	Trust authority unreachable
MCPS-008	Tool signature mismatch
MCPS-009	Insufficient trust level
MCPS-010	Rate limit exceeded
MCPS-011	Origin mismatch
MCPS-012	Transcript binding verification failed
MCPS-013	Passport exceeds maximum size
MCPS-014	Issuer chain exceeds maximum depth
MCPS-015	No mutually supported MCPS version

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Technical Details

• Signing: ECDSA P-256 (NIST FIPS 186-5)
• Signature format: IEEE P1363 fixed-length r||s (RFC 7518 Section 3.4)
• Low-S normalization: BIP-0062 signature malleability prevention
• Canonicalization: RFC 8785 JSON Canonicalization Scheme
• Nonce: 16 bytes cryptographic random (128-bit)
• Timestamp window: 5 minutes (configurable)
• Passport format: asp_ prefix + 32 hex chars
• Node.js: Zero dependencies (pure crypto built-in)
• Python: Single dependency (cryptography)
• 75 tests: Covering all cryptographic operations, edge cases, and attack vectors

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Specification

• IETF Internet-Draft: draft-sharif-mcps-secure-mcp-00 (2,405 lines)
• SEP-2395: Full specification -- submitted to MCP specification repo
• Playground: agentsign.dev/playground

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On-Premise

Run your own Trust Authority. Nothing phones home.

docker run -p 8080:8080 agentsign/server

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License

MIT. Patent pending (GB2604808.2).

Built by CyberSecAI Ltd.