Flow 15 --- Compact-Token Rotation (Re-Encrypt)

/*
 * 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
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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.exception.AnkaSecureSdkException;
import co.ankatech.ankasecure.sdk.model.EncryptResult;
import co.ankatech.ankasecure.sdk.model.ReencryptResult;

import java.util.Base64;
import java.util.Objects;
import java.util.Properties;

import static co.ankatech.ankasecure.sdk.examples.ExampleUtil.*;
import static java.nio.charset.StandardCharsets.UTF_8;

/**
 * Scenario 15 — Compact-Token Rotation (RSA-3072 → ML-KEM-768).
 *
 * <p>This example migrates a Compact&nbsp;JWE from a classical RSA-3072 key to
 * a post-quantum ML-KEM-768 key <em>entirely in memory</em>. The original
 * plaintext is never exposed to the client.</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-reencrypt2-source}
 * ({@code RSA-3072}) and target {@code cli-reencrypt2-target} ({@code ML-KEM-768}).
 * The {@code cli-reference} actor holds the cross-kid REENCRYPT grant on this pair
 * plus the atomic encrypt/decrypt grants on each endpoint.</p>
 *
 * <h3>Prerequisites</h3>
 * <ul>
 *   <li>A valid encrypted CLI initialisation file (credentials).</li>
 *   <li>An access-token with the scopes:
 *       <code>secure.encrypt</code>,
 *       <code>secure.reencrypt</code>.</li>
 *   <li>The {@code demo-cli} playground provisioned with the
 *       {@code cli-reencrypt2-source} / {@code cli-reencrypt2-target} grant.</li>
 * </ul>
 *
 * @author ANKATech Solutions Inc.
 * @since 3.0.0
 * @see ExampleUtil
 * @see ExamplePlaygroundKeys
 * @see AuthenticatedSdk
 */
public final class ExampleScenario15 {

    /** No instantiation &mdash; this class only exposes {@link #main(String[])}. */
    private ExampleScenario15() { }

    /**
     * Runs the compact-token rotation 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 15 START =====");
        System.out.println("""
                Purpose :
                  * Rotate a Compact JWE from RSA-3072 to ML-KEM-768.
                  * Uses the pre-provisioned granted cross-kid pair
                    (cli-reencrypt2-source / cli-reencrypt2-target)
                Steps   :
                  1) Resolve granted RSA-3072 source + ML-KEM-768 target kids.
                  2) Encrypt plaintext ➜ Compact JWE (RSA).
                  3) Re-encrypt JWE ➜ Compact JWE (ML-KEM).
                  4) Compare headers & print metadata.
                --------------------------------------------------------------""");

        try {
            Properties props = loadProperties();
            AuthenticatedSdk sdk = authenticate(props);
            ExamplePlaygroundKeys playground = ExamplePlaygroundKeys.from(props, sdk);
            runScenario(sdk, playground);
        } catch (Exception ex) {
            fatal("Scenario 15 failed", ex);
        }

        System.out.println("===== SCENARIO 15 END =====");
    }

    /* ====================================================================== */
    /**
     * Executes encryption and token rotation on the granted cross-kid pair.
     *
     * @param sdk        an authenticated {@link AuthenticatedSdk} instance
     * @param playground the pre-provisioned playground key resolver; must not be {@code null}
     * @throws AnkaSecureSdkException if any operation fails
     */
    private static void runScenario(final AuthenticatedSdk sdk,
                                    final ExamplePlaygroundKeys playground)
            throws AnkaSecureSdkException {

        /* 1 ── resolve granted cross-kid pair (data-plane SDK: no key creation) */
        final String srcKid = playground.requireKid("cli-reencrypt2-source"); // RSA-3072
        final String dstKid = playground.requireKid("cli-reencrypt2-target"); // ML-KEM-768
        System.out.println("[1] Source kid (RSA-3072)    -> " + srcKid);
        System.out.println("[1] Target kid (ML-KEM-768)  -> " + dstKid);

        /* 2 ── Encrypt plaintext ➜ Compact JWE (RSA) ------------------ */
        byte[] plaintext = "Compact-token rotation demo".getBytes(UTF_8);
        EncryptResult encRes = sdk.encrypt(srcKid, plaintext);
        String oldJwe = encRes.getJweToken();
        System.out.println("[2] Original JWE header    = " + protectedHeader(oldJwe));

        /* 3 ── Re-encrypt JWE ➜ ML-KEM key ---------------------------- */
        ReencryptResult renRes = sdk.reencrypt(dstKid, oldJwe);
        String newJwe = renRes.getJweToken();
        System.out.println("[3] Rotated  JWE header    = " + protectedHeader(newJwe));
        printReencryptMeta(renRes);

        /* 4 ── Verify header changed ---------------------------------- */
        boolean changed = !Objects.equals(
                protectedHeader(oldJwe),
                protectedHeader(newJwe));
        System.out.println(changed
                ? "[✔] SUCCESS – header changed as expected."
                : "[✘] FAILURE – header did not change!");
    }

    /** Extracts and Base64URL-decodes the protected-header segment. */
    private static String protectedHeader(final String compactJwe) {
        int dot = compactJwe.indexOf('.');
        if (dot <= 0) return "(invalid)";
        try {
            byte[] decoded = Base64.getUrlDecoder()
                    .decode(compactJwe.substring(0, dot));
            return new String(decoded, UTF_8);
        } catch (IllegalArgumentException ex) {
            return "(decode error)";
        }
    }
}