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 * Copyright (C) 2026, Leo Galambos
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 *    This product includes software developed by the Egothor project.
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package zeroecho.core.alg.mldsa;

import java.security.GeneralSecurityException;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.util.Arrays;

import zeroecho.core.spi.PrivateKeyImporter;

/**
 * Builder for importing ML-DSA private keys from encoded specifications.
 *
 * @since 1.0
 */
public final class MldsaPrivateKeyBuilder implements PrivateKeyImporter<MldsaPrivateKeySpec> {

    private static final String ALG = "ML-DSA";

    /**
     * Imports a private key from PKCS#8 encoding.
     *
     * @param spec encoded private key spec
     * @return imported private key
     * @throws GeneralSecurityException if the key cannot be parsed or the provider
     *                                  does not support ML-DSA
     */
    @Override
    public PrivateKey importPrivate(MldsaPrivateKeySpec spec) throws GeneralSecurityException {
        KeyFactory kf = (spec.providerName() == null) ? KeyFactory.getInstance(ALG)
                : KeyFactory.getInstance(ALG, spec.providerName());
        byte[] encoded = spec.encoded();
        try {
            return kf.generatePrivate(new PKCS8EncodedKeySpec(encoded));
        } finally {
            Arrays.fill(encoded, (byte) 0);
        }
    }
}
