---

name: schemapin title: SchemaPin description: Cryptographic tool schema verification to prevent MCP Rug Pull attacks — ECDSA P-256 signing, SHA-256 hashing, TOFU key pinning, .well-known discovery, signed revocation documents, and (v1.4-alpha across all four languages) signature expiration, DNS TXT cross-verification, and schema version binding (lineage chain) version: 1.4.0-alpha.2 stable_version: 1.3.0

SchemaPin Development Skills Guide

Purpose: This guide helps AI assistants quickly integrate SchemaPin into applications for cryptographic tool schema verification.

For Full Documentation: See the README, Technical Specification, and language-specific READMEs in each subdirectory.

What SchemaPin Does

SchemaPin prevents "MCP Rug Pull" attacks by enabling developers to cryptographically sign their tool schemas (ECDSA P-256 + SHA-256) and clients to verify schemas haven't been tampered with. It uses Trust-On-First-Use (TOFU) key pinning and RFC 8615 .well-known endpoints for public key discovery.

Part of the ThirdKey trust stack: SchemaPin (tool integrity) → AgentPin (agent identity) → Symbiont (runtime)

---

Quick Start by Language

Python

pip install schemapin

from schemapin.crypto import KeyManager, SignatureManager
from schemapin.core import SchemaPinCore

# Generate keys
private_key, public_key = KeyManager.generate_keypair()

# Sign a schema
core = SchemaPinCore()
canonical = core.canonicalize_schema(schema_dict)
signature = SignatureManager.sign_schema(private_key, canonical)

# Verify
is_valid = SignatureManager.verify_signature(public_key, canonical, signature)

JavaScript

npm install schemapin

import { KeyManager, SignatureManager, SchemaPinCore } from 'schemapin';

// Generate keys
const { privateKey, publicKey } = KeyManager.generateKeypair();

// Sign a schema
const core = new SchemaPinCore();
const canonical = core.canonicalizeSchema(schema);
const signature = await SignatureManager.signSchema(privateKey, canonical);

// Verify
const isValid = await SignatureManager.verifySignature(publicKey, canonical, signature);

Go

go get github.com/ThirdKeyAi/schemapin/[email protected]

import (
    "github.com/ThirdKeyAi/schemapin/go/pkg/core"
    "github.com/ThirdKeyAi/schemapin/go/pkg/crypto"
)

// Generate keys
km := crypto.NewKeyManager()
privKey, pubKey, _ := km.GenerateKeypair()

// Sign a schema
spc := core.NewSchemaPinCore()
canonical, _ := spc.CanonicalizeSchema(schema)
sig, _ := crypto.NewSignatureManager().SignSchema(privKey, canonical)

// Verify
valid, _ := crypto.NewSignatureManager().VerifySignature(pubKey, canonical, sig)

Rust

[dependencies]
schemapin = "1.3"

use schemapin::crypto::{generate_key_pair, sign_data, verify_signature};
use schemapin::core::SchemaPinCore;

// Generate keys
let key_pair = generate_key_pair()?;

// Sign
let core = SchemaPinCore::new();
let canonical = core.canonicalize_schema(&schema)?;
let signature = sign_data(&key_pair.private_key_pem, &canonical)?;

// Verify
let is_valid = verify_signature(&key_pair.public_key_pem, &canonical, &signature)?;

---

Core Concepts

1. Schema Canonicalization

Schemas are canonicalized (deterministic JSON serialization with sorted keys) before hashing. This ensures identical schemas always produce the same hash regardless of key ordering.

2. .well-known Discovery

Developers publish their public key at https://example.com/.well-known/schemapin.json:

from schemapin.utils import create_well_known_response

response = create_well_known_response(
    public_key_pem=public_key_pem,
    developer_name="Acme Corp",
    schema_version="1.2",
    revocation_endpoint="https://example.com/.well-known/schemapin-revocations.json"
)

3. TOFU Key Pinning

On first verification, the developer's public key fingerprint is pinned. Subsequent verifications reject different keys for the same domain — detecting key substitution attacks.

4. Verification Workflows

Online (standard):

workflow = SchemaVerificationWorkflow(pin_store)
result = workflow.verify_schema(schema, signature, "https://example.com")

Offline (v1.2.0 — no HTTP required):

from schemapin.verification import verify_schema_offline, KeyPinStore

pin_store = KeyPinStore()
result = verify_schema_offline(
    schema, signature_b64, domain, tool_id,
    discovery_data, revocation_doc, pin_store
)

---

v1.2.0 Features

Standalone Revocation Documents

Full guide with operational playbook, all four languages, and combined inline+standalone semantics: docs/revocation.md.

from schemapin.revocation import (
    build_revocation_document, add_revoked_key,
    check_revocation, check_revocation_combined, RevocationReason
)

doc = build_revocation_document("example.com")
add_revoked_key(doc, fingerprint, RevocationReason.KEY_COMPROMISE)
check_revocation(doc, some_fingerprint)  # raises if revoked

# In production, always use combined check (inline list + standalone doc):
check_revocation_combined(
    revoked_keys_list=discovery.revoked_keys,
    revocation_doc=doc,
    fingerprint=some_fingerprint,
)

Trust Bundles (Offline / Air-Gapped)

Pre-package discovery + revocation data for environments without internet:

from schemapin.bundle import SchemaPinTrustBundle

bundle = SchemaPinTrustBundle.from_json(bundle_json_str)
discovery = bundle.find_discovery("example.com")
revocation = bundle.find_revocation("example.com")

Pluggable Discovery Resolvers

from schemapin.resolver import (
    WellKnownResolver,    # HTTP .well-known lookups
    LocalFileResolver,    # Local JSON files
    TrustBundleResolver,  # In-memory trust bundles
    ChainResolver,        # First-match fallthrough
)

# Chain: try bundle first, fall back to HTTP
resolver = ChainResolver([
    TrustBundleResolver.from_json(bundle_json),
    WellKnownResolver(timeout=10),
])

Resolver-Based Verification

from schemapin.verification import verify_schema_with_resolver

result = verify_schema_with_resolver(
    schema, signature_b64, domain, tool_id,
    resolver, pin_store
)

---

v1.3.0 Features

SkillSigner — File-Based Skill Folder Signing

Sign entire skill directories (e.g., a folder containing SKILL.md) with ECDSA P-256. Produces a .schemapin.sig manifest alongside the files, proving no file has been tampered with.

Python:

from schemapin.skill import sign_skill, verify_skill_offline

# Sign a skill directory
sig = sign_skill("./my-skill/", private_key_pem, "example.com")
# Writes .schemapin.sig into ./my-skill/

# Verify offline
from schemapin.verification import KeyPinStore
result = verify_skill_offline("./my-skill/", discovery_data, sig, revocation_doc, KeyPinStore())

JavaScript:

import { signSkill, verifySkillOffline } from 'schemapin/skill';

const sig = await signSkill('./my-skill/', privateKeyPem, 'example.com');
const result = verifySkillOffline('./my-skill/', discoveryData, sig, revDoc, pinStore);

Go:

import "github.com/ThirdKeyAi/schemapin/go/pkg/skill"

sig, err := skill.SignSkill("./my-skill/", privateKeyPEM, "example.com", "", "")
result := skill.VerifySkillOffline("./my-skill/", disc, sig, rev, pinStore, "")

Rust:

use schemapin::skill::{sign_skill, verify_skill_offline};

let sig = sign_skill("./my-skill/", &private_key_pem, "example.com", None, None)?;
let result = verify_skill_offline("./my-skill/", &disc, Some(&sig), rev.as_ref(), Some(&pin_store), None);

.schemapin.sig Format

{
  "schemapin_version": "1.3",
  "skill_name": "my-skill",
  "skill_hash": "sha256:<root_hash>",
  "signature": "<base64_ecdsa_signature>",
  "signed_at": "2026-02-14T00:00:00Z",
  "domain": "example.com",
  "signer_kid": "sha256:<key_fingerprint>",
  "file_manifest": {
    "SKILL.md": "sha256:<file_hash>"
  }
}

Tamper Detection

from schemapin.skill import detect_tampered_files, canonicalize_skill

_, current_manifest = canonicalize_skill("./my-skill/")
tampered = detect_tampered_files(current_manifest, sig.file_manifest)
# tampered.modified, tampered.added, tampered.removed

---

v1.4.0-alpha.2 Features (all four languages — preview)

Schema Version Binding (schema_version + previous_hash)

Two additive optional fields on .schemapin.sig give publishers a way to declare lineage and verifiers a way to enforce it. Defends against rug-pull substitutions where an attacker swaps a tampered schema under the same name.

Rust:

use schemapin::skill::{sign_skill_with_options, SignOptions, verify_chain};

let v1 = sign_skill_with_options(&dir_v1, &priv_pem, "example.com",
    SignOptions::new().with_schema_version("1.0.0"))?;

let v2 = sign_skill_with_options(&dir_v2, &priv_pem, "example.com",
    SignOptions::new()
        .with_schema_version("1.1.0")
        .with_previous_hash(&v1.skill_hash))?;

verify_chain(&v2, &v1)?;  // Pure metadata check; both must already be cryptographically verified.

Python:

from schemapin.skill import SkillSigner, SignOptions, verify_chain
v2 = SkillSigner.sign_with_options(dir_v2, priv_pem, "example.com",
    SignOptions(schema_version="1.1.0", previous_hash=v1["skill_hash"]))
verify_chain(v2, v1)

JavaScript:

import { signSkillWithOptions, verifyChain } from 'schemapin';
const v2 = signSkillWithOptions(dirV2, privPem, 'example.com',
    { schemaVersion: '1.1.0', previousHash: v1.skill_hash });
verifyChain(v2, v1);

Go:

v2, _ := skill.SignSkillWithOptions(dirV2, privPEM, "example.com", skill.SignOptions{
    SchemaVersion: "1.1.0",
    PreviousHash:  v1.SkillHash,
})
err := skill.VerifyChain(v2, v1)

VerificationResult gains schema_version and previous_hash fields — verifiers surface these informationally. Chain enforcement is opt-in via verify_chain (or the language equivalent). ChainError distinguishes two failure modes: no_previous_hash (current sig lacks the field) and mismatch (both present but unequal — likely substitution).

Full guide: docs/schema-version-binding.md.

---

v1.4.0-alpha.1 Features (all four languages — preview)

Both features are additive optional fields/records: v1.3 verifiers ignore them, and v1.4 signatures without these fields behave identically to v1.3. Python, JavaScript, and Go ports follow in subsequent alphas before the v1.4.0 release.

Signature Expiration (expires_at)

Optional ISO 8601 / RFC 3339 timestamp on .schemapin.sig. Verifiers past the timestamp degrade the result (warning) instead of failing — valid stays true, expired becomes true, and a signature_expired warning is appended.

use schemapin::skill::{sign_skill_with_options, SignOptions, verify_skill_offline};

// Sign with a 180-day TTL — writes expires_at into .schemapin.sig
let opts = SignOptions::new().with_expires_in(chrono::Duration::days(180));
let sig = sign_skill_with_options(dir, &priv_pem, "example.com", opts)?;

// Verify — past expires_at returns valid=true with expired=true and a
// "signature_expired" warning, never a hard failure
let result = verify_skill_offline(dir, &discovery, None, None, None, Some("tool"));
if result.expired {
    log::warn!("signature past {}", result.expires_at.unwrap_or_default());
}

SignOptions is a builder; the legacy sign_skill(...) function is preserved for v1.3 callers and writes signatures without expires_at (still advertised as schemapin_version: "1.3").

DNS TXT Cross-Verification (_schemapin.{domain})

Tool providers MAY publish a TXT record alongside .well-known/schemapin.json:

_schemapin.example.com.  IN TXT  "v=schemapin1; kid=acme-2026-04; fp=sha256:a1b2c3..."

Cross-checking the TXT against the discovery key gives a second-channel verification — the DNS credential chain is independent of the HTTPS hosting one. Mismatch is a hard failure (DOMAIN_MISMATCH); absent record is a no-op.

use schemapin::dns::{parse_txt_record, fetch_dns_txt};
use schemapin::skill::verify_skill_offline_with_dns;

// Parser/matcher are always available
let txt = parse_txt_record("v=schemapin1; fp=sha256:a1b2c3...")?;

// Async fetch lives behind the `dns` Cargo feature (hickory-resolver)
#[cfg(feature = "dns")]
let txt = fetch_dns_txt("example.com").await?;

let result = verify_skill_offline_with_dns(
    dir, &discovery, None, None, None, Some("tool"), txt.as_ref(),
);

Cargo feature	Default	Brings in
fetch	off	reqwest, tokio, async-trait
dns (NEW)	off	hickory-resolver, tokio, async-trait

---

Server-Side Setup

Publishing .well-known Endpoints

Python CLI tools are included:

# Generate a keypair
schemapin-keygen --output-dir ./keys

# Sign a schema
schemapin-sign --key ./keys/private.pem --schema schema.json

# Verify a signature
schemapin-verify --key ./keys/public.pem --schema schema.json --signature sig.b64

Go CLI equivalents are also available (go install github.com/ThirdKeyAi/schemapin/go/cmd/[email protected]).

---

Architecture

Developer                          Client (AI Platform)
─────────                          ────────────────────
1. Generate ECDSA P-256 keypair
2. Publish public key at           3. Discover public key from
   /.well-known/schemapin.json        /.well-known/schemapin.json
4. Sign tool schema                5. Verify signature
   (canonicalize → SHA-256            (canonicalize → SHA-256
    → ECDSA sign)                      → ECDSA verify)
                                   6. TOFU pin the key fingerprint
                                   7. Check revocation status

---

Language API Reference

Operation	Python	JavaScript	Go	Rust
Generate keys	KeyManager.generate_keypair()	KeyManager.generateKeypair()	km.GenerateKeypair()	generate_key_pair()
Sign schema	SignatureManager.sign_schema()	SignatureManager.signSchema()	sm.SignSchema()	sign_data()
Verify signature	SignatureManager.verify_signature()	SignatureManager.verifySignature()	sm.VerifySignature()	verify_signature()
Canonicalize	SchemaPinCore().canonicalize_schema()	new SchemaPinCore().canonicalizeSchema()	spc.CanonicalizeSchema()	SchemaPinCore::new().canonicalize_schema()
Discover key	PublicKeyDiscovery.fetch_well_known()	PublicKeyDiscovery.fetchWellKnown()	FetchWellKnown()	WellKnownResolver (fetch feature)
Offline verify	verify_schema_offline()	verifySchemaOffline()	VerifySchemaOffline()	verify_schema_offline()
Resolver verify	verify_schema_with_resolver()	verifySchemaWithResolver()	VerifySchemaWithResolver()	verify_schema_with_resolver()
Sign skill folder	sign_skill()	signSkill()	skill.SignSkill()	sign_skill()
Verify skill	verify_skill_offline()	verifySkillOffline()	skill.VerifySkillOffline()	verify_skill_offline()
Detect tampering	detect_tampered_files()	detectTamperedFiles()	skill.DetectTamperedFiles()	detect_tampered_files()

---

Testing

# Python
cd python && python -m pytest tests/ -v

# JavaScript
cd javascript && npm test

# Go
cd go && go test ./...

# Rust
cd rust && cargo test

---

Pro Tips for AI Assistants

1. Always canonicalize before signing or verifying — raw JSON comparison will fail
2. Use offline verification when you have pre-fetched discovery data — avoids HTTP calls during schema validation
3. Trust bundles are ideal for CI/CD and air-gapped deployments
4. ChainResolver lets you layer resolvers: bundle → local files → HTTP as fallback
5. TOFU pinning means the first key seen for a domain is trusted — warn users on key changes
6. All languages use the same crypto — ECDSA P-256 + SHA-256, so cross-language verification works
7. Revocation checking should always be performed — both simple lists and standalone documents
8. SkillSigner signs entire directories — ideal for SKILL.md folders uploaded to registries like ClaWHub
9. .schemapin.sig is auto-excluded from hashing — you can re-sign a directory without removing the old signature first