sigil_ed25519.py

#!/usr/bin/env python3
"""Ed25519 SIGIL signing for SOV33 API endpoints.

Usage:
    from sigil_ed25519 import SigilSigner
    
    signer = SigilSigner()
    sigil = signer.sign({"action": "test", "timestamp": "2026-07-26"})
    assert signer.verify(sigil)
"""
import json
import hashlib
import time
from pathlib import Path

try:
    from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
    from cryptography.hazmat.primitives import serialization
    HAS_CRYPTO = True
except ImportError:
    HAS_CRYPTO = False


class SigilSigner:
    """Ed25519 SIGIL signer for sovereign actions."""
    
    def __init__(self, key_path=None):
        if not HAS_CRYPTO:
            raise ImportError("pip install cryptography")
        
        if key_path and Path(key_path).exists():
            self._load_key(key_path)
        else:
            self._generate_key(key_path)
    
    def _generate_key(self, save_path=None):
        """Generate new Ed25519 key pair."""
        self.private_key = Ed25519PrivateKey.generate()
        self.public_key = self.private_key.public_key()
        
        if save_path:
            Path(save_path).parent.mkdir(parents=True, exist_ok=True)
            # Save private key
            priv_pem = self.private_key.private_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PrivateFormat.PKCS8,
                encryption_algorithm=serialization.NoEncryption()
            )
            Path(save_path).write_bytes(priv_pem)
            Path(save_path).chmod(0o600)
            
            # Save public key
            pub_path = str(save_path) + ".pub"
            pub_pem = self.public_key.public_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PublicFormat.SubjectPublicKeyInfo
            )
            Path(pub_path).write_bytes(pub_pem)
    
    def _load_key(self, key_path):
        """Load existing Ed25519 key pair."""
        priv_pem = Path(key_path).read_bytes()
        self.private_key = serialization.load_pem_private_key(priv_pem, password=None)
        self.public_key = self.private_key.public_key()
    
    def sign(self, payload):
        """Create SIGIL signature for payload."""
        if isinstance(payload, dict):
            payload = json.dumps(payload, sort_keys=True).encode()
        elif isinstance(payload, str):
            payload = payload.encode()
        
        signature = self.private_key.sign(payload)
        
        return {
            "payload": payload.decode() if isinstance(payload, bytes) else payload,
            "signature": signature.hex(),
            "algorithm": "Ed25519",
            "timestamp": time.time(),
            "sha256": hashlib.sha256(payload).hexdigest()
        }
    
    def verify(self, sigil):
        """Verify SIGIL signature."""
        try:
            payload = sigil["payload"]
            if isinstance(payload, str):
                payload = payload.encode()
            
            signature = bytes.fromhex(sigil["signature"])
            self.public_key.verify(signature, payload)
            
            # Verify SHA256
            expected_hash = hashlib.sha256(payload).hexdigest()
            if sigil.get("sha256") != expected_hash:
                return False
            
            return True
        except Exception:
            return False
    
    def get_public_key_hex(self):
        """Get public key as hex string."""
        pub_bytes = self.public_key.public_bytes(
            encoding=serialization.Encoding.Raw,
            format=serialization.PublicFormat.Raw
        )
        return pub_bytes.hex()


class SigilChain:
    """Hash-chained SIGIL ledger."""
    
    def __init__(self, signer):
        self.signer = signer
        self.chain = []
        self.prev_hash = "genesis"
    
    def append(self, payload):
        """Append new SIGIL to chain."""
        chain_payload = {
            "payload": payload,
            "prev_hash": self.prev_hash,
            "chain_index": len(self.chain),
        }
        
        sigil = self.signer.sign(chain_payload)
        sigil["chain_hash"] = hashlib.sha256(
            (self.prev_hash + sigil["sha256"]).encode()
        ).hexdigest()
        
        self.chain.append(sigil)
        self.prev_hash = sigil["chain_hash"]
        
        return sigil
    
    def verify_chain(self):
        """Verify entire chain integrity."""
        prev_hash = "genesis"
        
        for i, sigil in enumerate(self.chain):
            # Verify signature
            if not self.signer.verify(sigil):
                return False, f"Signature invalid at index {i}"
            
            # Verify chain linkage
            expected_hash = hashlib.sha256(
                (prev_hash + sigil["sha256"]).encode()
            ).hexdigest()
            if sigil.get("chain_hash") != expected_hash:
                return False, f"Chain broken at index {i}"
            
            prev_hash = sigil["chain_hash"]
        
        return True, "Chain valid"


# Global signer instance
_signer = None

def get_signer(key_path="/workspace/sigil_key.pem"):
    """Get or create global signer."""
    global _signer
    if _signer is None:
        _signer = SigilSigner(key_path)
    return _signer


def sign_response(response_data):
    """Sign API response with SIGIL."""
    signer = get_signer()
    return signer.sign(response_data)


def verify_sigil(sigil):
    """Verify SIGIL signature."""
    signer = get_signer()
    return signer.verify(sigil)


if __name__ == "__main__":
    # Demo
    signer = SigilSigner("/tmp/sigil_demo_key.pem")
    
    # Sign
    sigil = signer.sign({"action": "test", "data": "hello world"})
    print("Signed:", json.dumps(sigil, indent=2)[:200])
    
    # Verify
    valid = signer.verify(sigil)
    print("Valid:", valid)
    
    # Chain demo
    chain = SigilChain(signer)
    chain.append({"step": 1, "data": "first"})
    chain.append({"step": 2, "data": "second"})
    chain.append({"step": 3, "data": "third"})
    
    valid, msg = chain.verify_chain()
    print(f"Chain: {len(chain.chain)} entries, valid={valid}, msg={msg}")