/**
 * @file cipher.ts
 * @description AEAD record protection for DTLS 1.2 with AES-128-GCM.
 * @module dtls/cipher
 *
 * Implements key derivation and the GCM record encrypt/decrypt for the suite
 * TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 (RFC 5288 / RFC 6347).
 *
 * Key block layout for AEAD (no MAC keys):
 *   client_write_key[16] | server_write_key[16] |
 *   client_write_IV[4]   | server_write_IV[4]      (implicit salt)
 *
 * GCM nonce  = write_IV (4) || explicit_nonce (8)
 * Record     = explicit_nonce (8) || ciphertext || tag (16)
 * AAD (DTLS) = seq_num (8 = epoch||seq) || type (1) || version (2) || plaintext_len (2)
 */
/**
 * Per-direction keys/IVs produced by {@link deriveKeys}.
 */
export interface DerivedKeys {
    clientKey: Buffer;
    serverKey: Buffer;
    clientIV: Buffer;
    serverIV: Buffer;
}
/**
 * Derive the master secret from the pre-master secret (RFC 5246 §8.1).
 * @param {Buffer} preMasterSecret
 * @param {Buffer} clientRandom - 32 bytes
 * @param {Buffer} serverRandom - 32 bytes
 * @returns {Buffer} 48-byte master secret
 */
export declare function deriveMasterSecret(preMasterSecret: Buffer, clientRandom: Buffer, serverRandom: Buffer): Buffer;
/**
 * Derive the extended master secret (RFC 7627) using the handshake hash.
 * @param {Buffer} preMasterSecret
 * @param {Buffer} sessionHash - hash of handshake messages through CKE
 * @returns {Buffer} 48-byte master secret
 */
export declare function deriveExtendedMasterSecret(preMasterSecret: Buffer, sessionHash: Buffer): Buffer;
/**
 * Expand the key block and split it into per-direction keys/IVs.
 * @param {Buffer} masterSecret
 * @param {Buffer} clientRandom
 * @param {Buffer} serverRandom
 * @returns {DerivedKeys}
 */
export declare function deriveKeys(masterSecret: Buffer, clientRandom: Buffer, serverRandom: Buffer): DerivedKeys;
/**
 * @class GcmCipher
 * @description Holds the key/IV for one direction and does record AEAD.
 */
export declare class GcmCipher {
    #private;
    /**
     * @param {Buffer} key - 16-byte AES key
     * @param {Buffer} fixedIv - 4-byte implicit salt
     */
    constructor(key: Buffer, fixedIv: Buffer);
    /**
     * Encrypt a record fragment.
     * @param {number} epoch
     * @param {number} seq
     * @param {number} type
     * @param {number} version
     * @param {Buffer} plaintext
     * @returns {Buffer} explicit_nonce || ciphertext || tag
     */
    encrypt(epoch: number, seq: number, type: number, version: number, plaintext: Buffer): Buffer;
    /**
     * Decrypt a record fragment.
     * @param {number} epoch
     * @param {number} seq
     * @param {number} type
     * @param {number} version
     * @param {Buffer} record - explicit_nonce || ciphertext || tag
     * @returns {Buffer} plaintext
     * @throws on authentication failure
     */
    decrypt(epoch: number, seq: number, type: number, version: number, record: Buffer): Buffer;
}