/**
 * federation/hmac.ts — HMAC-SHA-256 signing + verification for
 * federation envelopes.
 *
 * F-038 — security-critical. Pinned by AGENTS.md hard constraint:
 *   "MUST use crypto.timingSafeEqual for HMAC comparison
 *    (timing-attack resistant)."
 *   "MUST use crypto.randomUUID() for nonces (128-bit random)."
 *
 * Nonce strategy:
 *   - Sender generates a fresh `crypto.randomUUID()` per envelope.
 *   - Receiver tracks every nonce it has seen in a TTL-bounded Set.
 *   - An envelope whose nonce appears twice is a replay → reject.
 *   - An envelope whose timestamp is older than `nonceWindowMs`
 *     (default 5 min) is also a replay → reject.
 *
 * No native deps. Pure Node `node:crypto`.
 */
import { type FederationEnvelope } from "./envelope.js";
/** Default freshness window for HMAC verification (5 minutes). */
export declare const DEFAULT_NONCE_WINDOW_MS: number;
/** Compute a deterministic 64-char hex HMAC-SHA-256 over the envelope's
 *  canonical signable payload. */
export declare function signEnvelope<T>(envelope: FederationEnvelope<T>, secret: string): string;
export interface VerifyOptions {
    /** Freshness window. Envelopes older than this are rejected.
     *  Defaults to 5 minutes. */
    readonly nonceWindowMs?: number;
    /** Optional clock-skew offset (ms) to *add* to the freshness
     *  window (e.g. for poorly-synced peers). Defaults to 0. */
    readonly clockSkewMs?: number;
    /** Optional explicit timestamp for deterministic tests. */
    readonly now?: number;
}
export type VerifyOutcome = {
    ok: true;
} | {
    ok: false;
    reason: "signature_mismatch" | "nonce_replay" | "envelope_expired" | "envelope_from_future" | "invalid_signature_format";
};
/** Pure verifier — no shared state. The caller owns the seen-nonce
 *  cache (see `NonceCache` below) and passes it in via `seen`. */
export declare function verifySignature<T>(envelope: FederationEnvelope<T>, secret: string, seen: ReadonlySet<string>, opts?: VerifyOptions): VerifyOutcome;
/** Mutable nonce cache with TTL eviction + hard cap. The receiver
 *  keeps one per remote node (or a single global one for the skeleton). */
export declare class NonceCache {
    private readonly seen;
    private readonly windowMs;
    constructor(windowMs?: number);
    /** True if the nonce is fresh (not seen in windowMs). Adds it
     *  to the cache as a side effect. */
    check(nonce: string, now?: number): boolean;
    /** True if the nonce is in the cache (read-only). */
    has(nonce: string): boolean;
    size(): number;
    clear(): void;
    private evict;
}
/** Helper — produce a fresh nonce via `crypto.randomUUID()`. */
export declare function freshNonce(): string;
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