Flow 8 -- ML-KEM-768 ➜ ML-KEM-1024 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
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 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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 * 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.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 — ML-KEM-768 → ML-KEM-1024 Bulk Re-encryption (auto-detect / Compact JWE).
 *
 * <p>This scenario performs a <strong>non-streaming</strong> PQC-to-PQC migration
 * of ciphertext from an ML-KEM-768 key to a stronger ML-KEM-1024 key, entirely on
 * the server side (no plaintext exposure):</p>
 *
 * <p>The SDK is data-plane-only: it does not create keys. This scenario operates
 * on the <strong>pre-provisioned granted cross-kid pair</strong> of the
 * {@code demo-cli} playground &mdash; source {@code cli-reencrypt3-source}
 * ({@code ML-KEM-768}) and target {@code cli-reencrypt3-target} ({@code ML-KEM-1024}).
 * The {@code cli-reference} actor holds the cross-kid REENCRYPT grant on this pair
 * plus the atomic encrypt/decrypt grants on each endpoint.</p>
 *
 * <ol>
 *   <li>Resolve the granted {@code ML-KEM-768} source and {@code ML-KEM-1024} target kids.</li>
 *   <li>Encrypt a file under the source (auto-detected Compact&nbsp;JWE).</li>
 *   <li>Re-encrypt the ciphertext on the server (ML-KEM-768 &rarr; ML-KEM-1024).</li>
 *   <li>Decrypt the new KEM ciphertext under the target.</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 ExamplePlaygroundKeys
 * @see AuthenticatedSdk
 */
public final class ExampleScenario8 {

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

    /**
     * Runs the ML-KEM-768 to ML-KEM-1024 re-encryption scenario on the granted pair.
     *
     * <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 from ML-KEM-768 to ML-KEM-1024 (non-streaming helpers)
                  * Uses the pre-provisioned granted cross-kid pair
                    (cli-reencrypt3-source / cli-reencrypt3-target)
                  * Demonstrates encryptFile -> reencryptFile -> decryptFile APIs
                Steps   :
                  1) Resolve granted ML-KEM-768 source + ML-KEM-1024 target kids
                  2) Encrypt payload under source (auto-detected compact JWE)
                  3) Re-encrypt ciphertext to target
                  4) Decrypt KEM ciphertext under target
                  5) Validate integrity
                --------------------------------------------------------------""");

        try {
            prepareWorkingDir();

            Properties            props      = loadProperties();
            AuthenticatedSdk      sdk        = authenticate(props);
            ExamplePlaygroundKeys playground = ExamplePlaygroundKeys.from(props, sdk);

            runScenario(sdk, playground);

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

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

    /**
     * Executes the ML-KEM-768 to ML-KEM-1024 re-encryption scenario on the granted pair.
     *
     * <ol>
     *   <li>Create plaintext file.</li>
     *   <li>Resolve the granted ML-KEM-768 source and ML-KEM-1024 target kids.</li>
     *   <li>Encrypt under the source (auto-detected compact JWE).</li>
     *   <li>Re-encrypt the ciphertext to the target (server-side).</li>
     *   <li>Decrypt KEM ciphertext under the target.</li>
     *   <li>Validate round-trip integrity.</li>
     * </ol>
     *
     * @param sdk        an authenticated {@link AuthenticatedSdk} instance;
     *                   must not be {@code null}
     * @param playground the pre-provisioned playground key resolver; must not be {@code null}
     * @throws Exception if any step fails
     */
    private static void runScenario(final AuthenticatedSdk sdk,
                                    final ExamplePlaygroundKeys playground) throws Exception {

        /* 1 -- create plaintext --------------------------------------------- */
        Path plain = TEMP_DIR.resolve("scenario8_plain.txt");
        FileIO.writeUtf8(plain,
                "Scenario-8 - ML-KEM-768 -> ML-KEM-1024 bulk re-encrypt demo.");
        System.out.println("[1] Plaintext ready          -> " + plain.toAbsolutePath());

        /* 2 -- resolve granted cross-kid pair (data-plane SDK: no key creation) */
        final String srcKid = playground.requireKid("cli-reencrypt3-source"); // ML-KEM-768
        final String kemKid = playground.requireKid("cli-reencrypt3-target"); // ML-KEM-1024
        System.out.println("[2] Source kid (ML-KEM-768)  -> " + srcKid);
        System.out.println("[2] Target kid (ML-KEM-1024) -> " + kemKid);

        Path srcJwe = TEMP_DIR.resolve("scenario8_src.jwe");
        EncryptResult srcMeta = sdk.encryptFile(srcKid, plain, srcJwe);
        System.out.println("[2] Ciphertext (ML-KEM-768)  -> " + srcJwe.toAbsolutePath());
        printEncryptMeta(srcMeta);

        /* 3 -- server-side re-encryption ML-KEM-768 -> ML-KEM-1024 ---------- */
        Path kemJwe = TEMP_DIR.resolve("scenario8_kem.jwe");
        ReencryptResult reMeta = sdk.reencryptFile(kemKid, srcJwe, kemJwe);
        System.out.println("[3] Ciphertext (ML-KEM-1024) -> " + kemJwe.toAbsolutePath());
        printReencryptMeta(reMeta);

        /* 4 -- decrypt KEM ciphertext --------------------------------------- */
        Path recovered = TEMP_DIR.resolve("scenario8_dec.txt");
        DecryptResultMetadata decMeta = sdk.decryptFile(kemJwe, recovered);
        System.out.println("[4] Decrypted file           -> " + recovered.toAbsolutePath());
        printDecryptMeta(decMeta);

        /* 5 -- integrity check ---------------------------------------------- */
        boolean match = FileIO.readUtf8(plain)
                .equals(FileIO.readUtf8(recovered));
        System.out.println(match
                ? "[5] SUCCESS - plaintext matches."
                : "[5] FAILURE - plaintext mismatch.");
    }
}