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package java.security.interfaces;

import java.security.PrivateKey;

import java.util.Optional;

/**

 * An interface for an elliptic curve private key as defined by RFC 7748.

 * These keys are distinct from the keys represented by {@code ECPrivateKey},

 * and they are intended for use with algorithms based on RFC 7748 such as the

 * XDH {@code KeyAgreement} algorithm.

 *

 * An XEC private key is an encoded scalar value as described in RFC 7748.

 * The decoding procedure defined in this RFC includes an operation that forces

 * certain bits of the key to either 1 or 0. This operation is known as

 * "pruning" or "clamping" the private key. Arrays returned by this interface

 * are unpruned, and implementations will need to prune the array before

 * using it in any numerical operations.

 *

 * @since 11

 */

public interface XECPrivateKey extends XECKey, PrivateKey {

    /**

     * Get the scalar value encoded as an unpruned byte array. A new copy of

     * the array is returned each time this method is called.

     *

     * @return the unpruned encoded scalar value, or an empty Optional if the

     *     scalar cannot be extracted (e.g. if the provider is a hardware token

     *     and the private key is not allowed to leave the crypto boundary).

     */

    Optional<byte[]> getScalar();

}