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/**
 * Hybrid key exchange (KEX) utilities combining a classic agreement and a
 * post-quantum KEM-style agreement into one derived shared secret.
 *
 * <p>
 * This package provides an SDK-level composition layer over existing core
 * contracts:
 * </p>
 * <ul>
 * <li>{@link zeroecho.core.context.AgreementContext} for classic DH-style
 * agreements (e.g. X25519, ECDH, DH), and</li>
 * <li>{@link zeroecho.core.context.MessageAgreementContext} for message-based
 * agreements (typically PQC KEM-style flows such as ML-KEM exposed via
 * {@code KeyUsage.AGREEMENT}).</li>
 * </ul>
 *
 * <h2>Wire model</h2>
 * <p>
 * A hybrid exchange needs explicit "to-be-sent" bytes. This package unifies the
 * model by emitting a single peer message containing two length-prefixed parts:
 * </p>
 * <ol>
 * <li>classic message (often empty for classic agreements that only require a
 * peer public key),</li>
 * <li>PQC message (typically KEM ciphertext produced by
 * {@link zeroecho.core.context.MessageAgreementContext}).</li>
 * </ol>
 *
 * <h2>Key derivation</h2>
 * <p>
 * The two underlying secrets are combined using HKDF-SHA256 (RFC 5869) via
 * {@link zeroecho.sdk.util.Kdf#hkdfSha256(byte[], byte[], byte[], int)} rather
 * than concatenation. Callers should treat raw intermediate secrets as
 * sensitive and clear them as soon as possible.
 * </p>
 *
 * <h2>Intended usage</h2>
 * <p>
 * Use {@link zeroecho.sdk.hybrid.kex.HybridKexContexts} to build initiator and
 * responder contexts and exchange
 * {@link zeroecho.sdk.hybrid.kex.HybridKexContext#getPeerMessage()} between
 * parties.
 * </p>
 *
 * @since 1.0
 */
package zeroecho.sdk.hybrid.kex;
