import type { EncBlob } from './session.types';
/** Encrypt UTF-8 text using AES-256-GCM. Returns base64url fields. */
export declare function encryptAesGcm(key: Buffer, plaintext: string): EncBlob;
/** Decrypt an AES-256-GCM blob (base64url fields) to UTF-8 text. */
export declare function decryptAesGcm(key: Buffer, blob: EncBlob): string;
/** HKDF-SHA256 (RFC 5869) to derive key material. */
export declare function hkdfSha256(ikm: Buffer, salt: Buffer, info: Buffer, length: number): Buffer;