Flow 8 -- P-521 ➜ ML-KEM-768 Compact-JWE Re-Encrypt (Non-Streaming)

/*
 * Copyright 2025 ANKATech Solutions Inc
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * SPDX-License-Identifier: Apache-2.0
 */
package co.ankatech.ankasecure.sdk.examples;

import co.ankatech.ankasecure.sdk.AuthenticatedSdk;
import co.ankatech.ankasecure.sdk.model.DecryptResultMetadata;
import co.ankatech.ankasecure.sdk.model.EncryptResult;
import co.ankatech.ankasecure.sdk.model.GenerateKeySpec;
import co.ankatech.ankasecure.sdk.model.ReencryptResult;
import co.ankatech.ankasecure.sdk.util.FileIO;

import java.nio.file.Path;
import java.util.Properties;

import static co.ankatech.ankasecure.sdk.examples.ExampleUtil.*;

/**
 * Scenario 8 — P-521 → ML-KEM-768 Bulk Re-encryption (Compact JWE).
 *
 * <p>This scenario performs a <strong>non-streaming</strong> migration of
 * ciphertext from a classical P-521 key to a post-quantum ML-KEM-768 key,
 * entirely on the server side (no plaintext exposure):</p>
 *
 * <ol>
 *   <li>Generate a P-521 key and encrypt a file (Compact&nbsp;JWE).</li>
 *   <li>Generate an ML-KEM-768 key.</li>
 *   <li>Re-encrypt the EC ciphertext on the server (P-521 &rarr; ML-KEM-768).</li>
 *   <li>Decrypt the new KEM ciphertext.</li>
 *   <li>Validate round-trip integrity.</li>
 * </ol>
 *
 * <p><b>Implementation notes (Java&nbsp;21+):</b></p>
 * <ul>
 *   <li>Filesystem operations rely on the {@link java.nio.file.Path} API.</li>
 *   <li>UTF-8 encoding is enforced explicitly for deterministic behaviour.</li>
 *   <li>Temporary artefacts are written under <kbd>temp_files/</kbd>.</li>
 * </ul>
 *
 * <p><b>Thread-safety:</b> this class is stateless and immutable.</p>
 *
 * @author ANKATech Solutions Inc.
 * @since 3.0.0
 * @see ExampleUtil
 * @see AuthenticatedSdk
 */
public final class ExampleScenario8 {

    /** No instantiation &mdash; this class only exposes {@link #main(String[])}. */
    private ExampleScenario8() { }

    /**
     * Runs the P-521 to ML-KEM-768 compact JWE re-encryption scenario.
     *
     * <p>Loads CLI properties, authenticates against ANKASecure&copy;,
     * and delegates to the scenario logic. On any unrecoverable error
     * the JVM terminates via
     * {@link ExampleUtil#fatal(String, Throwable)}.</p>
     *
     * @param args command-line arguments (ignored)
     */
    public static void main(final String[] args) {

        System.out.println("===== SCENARIO 8 START =====");
        System.out.println("""
                Purpose :
                  * Re-encrypt Compact-JWE from P-521 to ML-KEM-768 (non-streaming helpers)
                  * Demonstrates encryptFile -> reencryptFile -> decryptFile APIs
                Steps   :
                  1) Generate P-521 key
                  2) Encrypt payload (compact JWE)
                  3) Generate ML-KEM-768 key
                  4) Re-encrypt ciphertext
                  5) Decrypt KEM ciphertext
                  6) Validate integrity
                --------------------------------------------------------------""");

        try {
            ensureTempDir(TEMP_DIR);

            Properties   props = loadProperties();
            AuthenticatedSdk sdk  = authenticate(props);

            runScenario(sdk);

        } catch (Exception ex) {
            fatal("Scenario 8 failed", ex);
        }

        System.out.println("===== SCENARIO 8 END =====");
    }

    /**
     * Executes the 6-step P-521 to ML-KEM-768 re-encryption scenario.
     *
     * <ol>
     *   <li>Create plaintext file.</li>
     *   <li>Generate P-521 key and encrypt.</li>
     *   <li>Generate ML-KEM-768 key.</li>
     *   <li>Re-encrypt EC ciphertext to KEM (server-side).</li>
     *   <li>Decrypt KEM ciphertext.</li>
     *   <li>Validate round-trip integrity.</li>
     * </ol>
     *
     * @param sdk an authenticated {@link AuthenticatedSdk} instance;
     *            must not be {@code null}
     * @throws Exception if any step fails
     */
    private static void runScenario(final AuthenticatedSdk sdk) throws Exception {

        /* 1 -- create plaintext --------------------------------------------- */
        Path plain = TEMP_DIR.resolve("scenario8_plain.txt");
        FileIO.writeUtf8(plain,
                "Scenario-8 - P-521 -> ML-KEM-768 bulk re-encrypt demo.");
        System.out.println("[1] Plaintext ready          -> " + plain.toAbsolutePath());

        /* 2 -- P-521 key + encrypt ------------------------------------------ */
        String ecKid = "sc8_p521_" + System.currentTimeMillis();
        sdk.generateKey(new GenerateKeySpec()
                .setKid(ecKid)
                .setKty("EC")
                .setAlg("P-521"));
        System.out.println("[2] P-521 key generated      -> kid = " + ecKid);

        Path ecJwe = TEMP_DIR.resolve("scenario8_ec.jwe");
        EncryptResult ecMeta = sdk.encryptFile(ecKid, plain, ecJwe);
        System.out.println("[2] Ciphertext (P-521)       -> " + ecJwe.toAbsolutePath());
        printEncryptMeta(ecMeta);

        /* 3 -- ML-KEM-768 key ----------------------------------------------- */
        String kemKid = "sc8_kem768_" + System.currentTimeMillis();
        sdk.generateKey(new GenerateKeySpec()
                .setKid(kemKid)
                .setKty("ML-KEM")
                .setAlg("ML-KEM-768"));
        System.out.println("[3] ML-KEM-768 key generated -> kid = " + kemKid);

        /* 4 -- server-side re-encryption EC -> KEM -------------------------- */
        Path kemJwe = TEMP_DIR.resolve("scenario8_kem.jwe");
        ReencryptResult reMeta = sdk.reencryptFile(kemKid, ecJwe, kemJwe);
        System.out.println("[4] Ciphertext (ML-KEM)      -> " + kemJwe.toAbsolutePath());
        printReencryptMeta(reMeta);

        /* 5 -- decrypt KEM ciphertext --------------------------------------- */
        Path recovered = TEMP_DIR.resolve("scenario8_dec.txt");
        DecryptResultMetadata decMeta = sdk.decryptFile(kemJwe, recovered);
        System.out.println("[5] Decrypted file           -> " + recovered.toAbsolutePath());
        printDecryptMeta(decMeta);

        /* 6 -- integrity check ---------------------------------------------- */
        boolean match = FileIO.readUtf8(plain)
                .equals(FileIO.readUtf8(recovered));
        System.out.println(match
                ? "[6] SUCCESS - plaintext matches."
                : "[6] FAILURE - plaintext mismatch.");
    }
}