k
108 lines
3.7 KiB
Python
108 lines
3.7 KiB
Python
"""
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Signed-request verification: EIP-191 signature that binds {action, wallet, timestamp, body}.
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Message format (human-readable — what the user sees in MetaMask):
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TrumpSignal · {ACTION}
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wallet: 0x...
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timestamp: 1713724800000
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body: <sha256_hex_of_canonical_json, or "-" for empty>
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Server verifies:
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1. recovered signer == wallet
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2. |now - timestamp| <= MAX_SKEW_SECONDS (5 min)
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3. sha256(canonical_json(body)) matches the hash in the message
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4. signature not seen before (replay cache, TTL = MAX_SKEW)
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Same scheme is used for writes (with body) and reads (body=None → "-").
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"""
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import hashlib
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import json
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import logging
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import time
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from typing import Any, Optional
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from eth_account import Account
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from eth_account.messages import encode_defunct
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from fastapi import HTTPException
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logger = logging.getLogger(__name__)
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MAX_SKEW_SECONDS = 300 # 5 minutes
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def canonical_body_hash(body: Optional[Any]) -> str:
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"""Stable sha256 of a Python dict/primitive. `None` → '-'."""
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if body is None:
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return "-"
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payload = json.dumps(body, sort_keys=True, separators=(",", ":"), default=str)
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return hashlib.sha256(payload.encode("utf-8")).hexdigest()
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def build_message(action: str, wallet: str, timestamp_ms: int, body_hash: str) -> str:
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return (
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f"TrumpSignal · {action}\n"
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f"wallet: {wallet.lower()}\n"
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f"timestamp: {timestamp_ms}\n"
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f"body: {body_hash}"
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)
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# ── Replay cache ──────────────────────────────────────────────────────────
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# In-memory; fine for a single-process deploy. For multi-worker, move to Redis.
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_seen: dict[str, float] = {} # sha256(signature) → expiry epoch seconds
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def _cache_put(sig: str, ttl: float) -> bool:
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"""Return True if sig was new, False if replay."""
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now = time.time()
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# lazy purge
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if len(_seen) > 5000:
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for k, v in list(_seen.items()):
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if v < now:
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_seen.pop(k, None)
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key = hashlib.sha256(sig.encode("utf-8")).hexdigest()
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if key in _seen and _seen[key] > now:
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return False
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_seen[key] = now + ttl
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return True
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# ── Public API ────────────────────────────────────────────────────────────
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def verify_signed_request(
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*,
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action: str,
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wallet: str,
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timestamp_ms: int,
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signature: str,
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body: Optional[Any],
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allow_replay: bool = False,
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) -> None:
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"""Raise HTTPException(401/422) if invalid. Silent on success.
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allow_replay=True skips the nonce cache — use only for idempotent reads
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(e.g. GET /user). Timestamp expiry still bounds the window to MAX_SKEW.
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"""
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wallet = wallet.lower().strip()
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# 1. Freshness
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now_ms = int(time.time() * 1000)
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if abs(now_ms - timestamp_ms) > MAX_SKEW_SECONDS * 1000:
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raise HTTPException(401, "Signed request expired or clock skew too large")
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# 2. Recover signer
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body_hash = canonical_body_hash(body)
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message = build_message(action, wallet, timestamp_ms, body_hash)
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try:
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recovered = Account.recover_message(encode_defunct(text=message), signature=signature).lower()
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except Exception as exc:
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logger.warning("Signature recovery failed (%s): %s", action, exc)
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raise HTTPException(401, "Signature verification failed")
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if recovered != wallet:
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raise HTTPException(401, "Signature does not match wallet")
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# 3. Replay guard (writes only)
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if not allow_replay:
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if not _cache_put(signature, ttl=MAX_SKEW_SECONDS):
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raise HTTPException(401, "Signature already used (replay blocked)")
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