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Flow 9 -- RSA-2048 ➜ ML-DSA-65 Compact-JWS Re-Sign (Non-Streaming)

This scenario shows how to upgrade an existing signature from a classical RSA scheme to a post-quantum ML-DSA-65 key without re-uploading the original data:

  • Generate an RSA-2048 key (oldKid).

  • Sign a file → compact JWS.

  • Generate an ML-DSA-65 key (newKid).

  • Re-sign the very same payload RSA ➜ ML-DSA-65 on the server.

  • Verify both the old and the new signature.

Key points

  • Uses the helper trio signFile → verifySignature → resignFile (entire token handled in memory).

  • Demonstrates a zero-plaintext signature migration---only the detached JWS leaves the service.

  • Produces rich telemetry for every step (key actually used, algorithm, warnings).

When to use it

  • Long-term manifest hardening -- refresh existing RSA signatures in software bills of materials or firmware bundles so they remain trustworthy after quantum breakthroughs.

  • Regulatory migrations -- meet PQC deadlines without touching or re-hashing the original artefacts.

  • Hybrid release workflows -- keep legacy RSA signatures for backward compatibility while attaching a forward-secure ML-DSA token in a single API pass.

Shared helper – this code imports the utility class from
example_util.md (configuration, authentication, JSON).

Complete Java implementation

src/main/java/co/ankatech/ankasecure/sdk/examples/ExampleScenario9.java 

/* *****************************************************************************
 * FILE: ExampleScenario9.java
 * Copyright © 2025 Anka Technologies.
 * SPDX-License-Identifier: MIT
 * ---------------------------------------------------------------------------
 * Scenario 9 – RSA-2048 → ML-DSA-65 Bulk Re-sign (Compact JWS helpers)
 * ---------------------------------------------------------------------------
 *  1. Generate an RSA-2048 key and sign a file → Compact JWS.
 *  2. Verify the RSA-based signature.
 *  3. Generate an ML-DSA-65 key.
 *  4. Re-sign exactly the same payload on the server (RSA → ML-DSA).
 *  5. Verify the fresh ML-DSA JWS.
 *  6. Print rich server metadata at every step.
 *
 * All transient artefacts are stored in <temp_files/>.
 * ****************************************************************************/
package co.ankatech.ankasecure.sdk.examples;

import co.ankatech.ankasecure.sdk.AnkaSecureSdk;
import co.ankatech.ankasecure.sdk.exception.AnkaSecureSdkException;
import co.ankatech.ankasecure.sdk.model.GenerateKeySpec;
import co.ankatech.ankasecure.sdk.model.ResignResult;
import co.ankatech.ankasecure.sdk.model.SignResult;
import co.ankatech.ankasecure.sdk.model.VerifySignatureResult;
import co.ankatech.ankasecure.sdk.util.FileIO;

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

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

/**
 * <h2>Scenario&nbsp;9 – RSA-2048 → ML-DSA-65 Bulk Re-sign (Compact&nbsp;JWS)</h2>
 *
 * <p>This scenario migrates a Compact&nbsp;JWS signature from a classical
 * RSA-2048 key to a post-quantum ML-DSA-65 key without requiring the client to
 * upload the payload again:</p>
 *
 * <ol>
 *   <li>Generate an RSA-2048 key and sign a file.</li>
 *   <li>Verify the RSA-based JWS.</li>
 *   <li>Generate an ML-DSA-65 key.</li>
 *   <li>Re-sign the payload on the server (RSA → ML-DSA).</li>
 *   <li>Verify the fresh ML-DSA JWS.</li>
 * </ol>
 *
 * <p><b>Implementation notes (Java&nbsp;21+):</b></p>
 * <ul>
 *   <li>Filesystem APIs use {@link java.nio.file.Path} exclusively.</li>
 *   <li>UTF-8 encoding is specified explicitly for deterministic behaviour.</li>
 *   <li>Temporary directories are created via {@link ExampleUtil#ensureTempDir(Path)}.</li>
 * </ul>
 *
 * <p><b>Thread-safety:</b> this class is stateless and immutable.</p>
 *
 * @author ANKATech – Security Engineering
 * @since 2.1.0
 */
public final class ExampleScenario9 {

    /* --------------------------------------------------------------------- */
    /** Working directory for artefacts. */
    private static final Path DATA_FILE = TEMP_DIR.resolve("scenario9_data.txt");
    private static final Path OLD_JWS   = TEMP_DIR.resolve("scenario9_rsa.jws");
    private static final Path NEW_JWS   = TEMP_DIR.resolve("scenario9_mldsa.jws");

    /* ===================================================================== */
    /**
     * Entry-point.
     *
     * @param args ignored
     */
    public static void main(final String[] args) {

        System.out.println("===== SCENARIO 9 START =====");
        System.out.println("""
                Purpose :
                  * Re-sign a Compact JWS from RSA-2048 to ML-DSA-65 (non-streaming helpers)
                  * Demonstrates signFile → verifySignature → resignFile → verifySignature
                --------------------------------------------------------------""");

        try {
            ensureTempDir(TEMP_DIR);

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

            runScenario(sdk);

        } catch (Exception ex) {
            fatal("Scenario 9 failed", ex);
        }

        System.out.println("===== SCENARIO 9 END =====");
    }

    /* ===================================================================== */
    /**
     * Executes all steps of Scenario&nbsp;9.
     *
     * @param sdk an authenticated {@link AnkaSecureSdk} instance
     *
     * @throws Exception if any operation fails
     */
    private static void runScenario(final AnkaSecureSdk sdk) throws Exception {

        /* 1 ── sample data ------------------------------------------------- */
        FileIO.writeUtf8(
                DATA_FILE,
                "Scenario-9 – bulk re-sign RSA-2048 → ML-DSA-65.");
        System.out.println("[1] Data file              -> " + DATA_FILE.toAbsolutePath());

        /* 2 ── RSA-2048 key + sign --------------------------------------- */
        String rsaKid = "sc9_rsa2048_" + System.currentTimeMillis();
        generateKey(sdk, rsaKid, "RSA", "RSA-2048");

        SignResult rsaSign = sdk.signFile(rsaKid, DATA_FILE, OLD_JWS);
        System.out.println("[2] RSA-2048 JWS created   -> " + OLD_JWS.toAbsolutePath());
        printSignMeta("RSA-2048 SIGN", rsaSign);

        VerifySignatureResult rsaVerify = sdk.verifySignature(OLD_JWS);
        printVerifyMeta("RSA-2048 VERIFY", rsaVerify);

        /* 3 ── ML-DSA-65 key -------------------------------------------- */
        String dsaKid = "sc9_mldsa65_" + System.currentTimeMillis();
        generateKey(sdk, dsaKid, "ML-DSA", "ML-DSA-65");

        /* 4 ── re-sign payload ------------------------------------------ */
        ResignResult reMeta = sdk.resignFile(dsaKid, OLD_JWS, NEW_JWS);
        System.out.println("[4] ML-DSA-65 JWS created  -> " + NEW_JWS.toAbsolutePath());
        printResignMeta(reMeta);

        /* 5 ── verify new JWS ------------------------------------------- */
        VerifySignatureResult dsaVerify = sdk.verifySignature(NEW_JWS);
        printVerifyMeta("ML-DSA-65 VERIFY", dsaVerify);

        System.out.println(dsaVerify.isValid()
                ? "[6] SUCCESS – new JWS is valid."
                : "[6] FAILURE – new JWS is INVALID.");
    }

    /* ---------- helper: key generation ----------------------------------- */
    private static void generateKey(final AnkaSecureSdk sdk,
                                    final String kid,
                                    final String kty,
                                    final String alg) throws AnkaSecureSdkException {

        sdk.generateKey(new GenerateKeySpec()
                .setKid(kid)
                .setKty(kty)
                .setAlg(alg));
        System.out.printf("    * Key generated -> kid=%s, alg=%s%n", kid, alg);
    }

    /**
     * Private constructor prevents instantiation.
     */
    private ExampleScenario9() {
        /* utility class – no instantiation */
    }
}

How to run

mvn -q compile exec:java\
  -Dexec.mainClass="co.ankatech.ankasecure.sdk.examples.ExampleScenario9"

Console milestones

  • RSA-2048 key generation & compact-JWS signature

  • Successful verification of the RSA signature

  • ML-DSA-65 key generation

  • Server-side re-sign → new ML-DSA compact JWS

  • Verification of the new post-quantum signature → SUCCESS

Where next?