/**
 * sha256 / hmacSha256 — Web Crypto API wrappers.
 *
 * Zero external dependencies. Uses globalThis.crypto.subtle (Node ≥ 19 native,
 * browser, Deno, Cloudflare Workers). Throws if the runtime does not expose
 * SubtleCrypto (Node < 19 without --experimental-global-webcrypto).
 *
 * @module proof/sha256
 */
/**
 * SHA-256 hex digest via Web Crypto.
 *
 * @param input - UTF-8 string or raw bytes.
 * @returns Lowercase hex digest (64 chars).
 * @throws If SubtleCrypto is unavailable.
 */
export declare function sha256(input: string | Uint8Array): Promise<string>;
/**
 * HMAC-SHA-256 hex digest via Web Crypto.
 *
 * @param key   - Raw key bytes (min 32 bytes recommended for HMAC-SHA-256).
 * @param input - UTF-8 string or raw bytes to authenticate.
 * @returns Lowercase hex MAC (64 chars).
 * @throws If SubtleCrypto is unavailable or key import fails.
 */
export declare function hmacSha256(key: Uint8Array, input: string | Uint8Array): Promise<string>;
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