@inversealtruism/csd-siwc

Sign in with CSD: an EIP-4361 / CAIP-122 analogue for the Compute Substrate. A relying party (RP) asks a wallet to sign a canonical, human-readable message bound to the RP's domain, a single-use nonce, and the chain id; the RP then verifies the signature server-side and derives the account only from the recovered key (never from a client-supplied address field).

import { buildSiwcMessage, signSiwc, verifySiwc, generateNonce, rfc3339, CSD_CHAIN_MAINNET } from "@inversealtruism/csd-siwc";

// RP issues a nonce, wallet builds + signs:
const fields = { domain: "app.example", account, uri: "https://app.example/login", version: "1",
  chainId: CSD_CHAIN_MAINNET, nonce, issuedAt: rfc3339(Date.now()), expirationTime: rfc3339(Date.now() + 600_000) };
const { message, sig64, pub33 } = signSiwc(fields, priv);

// RP verifies (fail-closed). `account` is the PROVEN signer.
const r = verifySiwc({ message, sig64, pub33 }, { domain: "app.example", nonce, chainId: CSD_CHAIN_MAINNET });
if (r.ok) grantSession(r.account);

Security model

• Domain-separated digest: sha256d(tagged_hash("CSD-SIWC-v1", utf8(message))) is disjoint from the tx sighash (CSD_SIG_V1) and the legacy login digest, so a sign-in signature can never be replayed as a transaction or a legacy login.
• Canonical round-trip gate: verifySiwc re-builds the parsed fields and rejects unless the bytes match, closing line-injection / field-smuggling. Field values reject all line terminators (incl. U+2028/2029/0085).
• Time bounds: timestamps MUST carry an explicit timezone (RFC3339 Z/offset; a zoneless time is rejected to avoid per-server-TZ divergence). issuedAt must be ≤ now + futureSkew (default 120s, tolerating normal NTP drift; set futureSkewMs to tighten/loosen) and not older than ~1h; expirationTime is required.
• Nonce + audience: single-use nonce and per-RP domain binding are the RP's responsibility (the library is stateless and binds audience via the message bytes).

Cross-language parity (digest + canonical message) is pinned by conformance/siwc_ref.py (a Python reference) and conformance/crosscheck-siwc.mjs. License: MIT.