(Android™) How to Generate a JSON Web Key (JWK)

Demonstrates how to generate the following types of JSON Web Keys:

• RSA key pair
• EC key pair
• Octet sequence key (HMAC-256)
• 192-bit AES GCM key

Note: This example requires Chilkat v9.5.0.66 or later.

Chilkat Android™ Downloads Android™ Java Libraries Android C/C++ Libraries

// Important: Don't forget to include the call to System.loadLibrary
// as shown at the bottom of this code sample.
package com.test;

import android.app.Activity;
import com.chilkatsoft.*;

import android.widget.TextView;
import android.os.Bundle;

public class SimpleActivity extends Activity {

  private static final String TAG = "Chilkat";

  // Called when the activity is first created.
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // This requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // ----------------------------------------------
    // Generate an RSA key pair in JWK format.
    // (Examples for generating other key types are shown below...)
    CkRsa rsa = new CkRsa();
    boolean success = rsa.GenerateKey(2048);
    CkPrivateKey rsaKey = rsa.ExportPrivateKeyObj();
    String rsaJwkStr = rsaKey.getJwk();

    // The string returned is the most compact possible, and therefore it is not
    // very readable.  To pretty-print, load into a JSON object and emit..
    CkJsonObject json = new CkJsonObject();
    json.put_EmitCompact(false);
    json.Load(rsaJwkStr);
    Log.i(TAG, json.emit());

    // Sample RSA JWK:

    // { 
    //   "kty": "RSA",
    //   "n": "6w1Xpof7gKmytJ3yc_yjI5_K3MvVXnBYBDy5Oh2W6Xqu_fOl3W18SjS2AU5xJrTHlB_j84yQjPyXJh_ixjACK4K4dCSYqlLmn3R7QJ84vnHLIEkqwUICqOHdCBjK5xhMrdZxIhuNlJzbARY-3u9RqjsT3HYTjA6JNHUWTYBBRou4gYGm4cJgvX4uexdikqxnze014RmZMaOV_4MR--WL4G8QfNJ2pRBEXQeKyije89H6M5oTSK7KZqFTIqu9hwNtx2oGpGAIcS0Jv5xVl-hDtwXZNwQJaOxMzLw1nwnb2kMliJa67EabQFrQY_xthQNsfzcHJJlpqYiMprW8wRkzmQ",
    //   "e": "AQAB",
    //   "d": "1_bnXMw-SeYhmxAwb19lqVqtMpdaES5ZwHLmoT4EpbsiQ5T1BfENrMSnoaWoEy8w3Kk8cU7qlY-TdOUBIKWFqOKvhY8GciA_Y6zLfgGNSnYVczGmxfBXr0HvKvxUmWZbNbH9OqBkQnKoSmRdGcp7l1Q2mG4o4ZuNdxRJjKXV0_DTrNLUJzst0hsfoZ6mWUrQcn39XGvvLjz9ySS-DYGI1vli3ayx8jVNuw0rU8UXVs9WmPQLvZO_ZDMhoLEeKsdejnNkUNPAUjqxcSOZRojt4BfCmbt-_1slFb0NsoaqnDVZGezd9J9ocxGuyIWHAJu9GGZEcdaFyiDDs_WA1IS_fQ",
    //   "p": "9dU8f6yOklRcpV6ayVMKpyQ6AMuBTF3rZmB498eAvvTkVG1-upm8IkikTVNpPjEalc82Sxuq8oF4N5x1-F33sgVEoCZG-1WFZTn-rnPnXSALES9hqSaVYEwnh61EiY8ckjBVr9jD2nL1JKdbfgVVeo69-9PdjnKYYDVL8eLNPwM",
    //   "q": "9MX2sW0GyaOsZ86AYe3eG2ZgcgKHvhJa573gih5Jvi2e-Nv-L0EVK29_DA7n0Pjm-gl9zVAsGsMMkphJyEF9QgyUlJ-59XLqWnECS5gO6WZdtHrJxVvcO-_AOrLIxeYnYcwhmaVaxs_UEpqGzupKHCWgf4cfXe49lrIsqGKH4jM",
    //   "dp": "IQgj9uvSxGq9gCL0HXUhC1Bc0tqFZyN_i-QOnQybig0R2R5VVvFtTBYCrbk1fPvQHK0ZGIKBN9CZvK8zUsodjDgU_ofmJcNaBz4BsKM2RVcW5Zo-PyJGFAhnj12CxhEKv8Hq4ZP4zROBSQmLy6Uf1TX05S-Up51SSCshJ0FYXs0",
    //   "dq": "RijsMiUfGfL5OvP85pUI4e-xW1yQThHyzpQlZVGTL5jiBVEBhcfw6ndWAj3Pgp2ljyvjTFNboPwhgW93Tpg-8AytFgDGi605sVzNHJ_kPlBiMZY0eYaAFQn-npSaaecziJu7UdAMugneLsruMycCwRij7Ynsmr7sFmLR3B4J9vM",
    //   "qi": "jZE-a1pa8YjflpCSH5oqp1f6f6I6-hpZcLdamLCoAcjVSIPk86gtXtOFES4411-DqYzYIZM6B_g_SRYY6JpKAOuZ40mmMTlnIEoVf8BHiGl3g6bBAiN1yQGXrwXJsg2OYnocyRA-xWNdcMSSFA52SwEdar2Mmw29qVzxtC1QbpA"
    // }

    // ----------------------------------------------
    // Generate an EC P-256 key pair in JWK format

    CkPrng prng = new CkPrng();
    CkEcc ecc = new CkEcc();
    CkPrivateKey ecKey = ecc.GenEccKey("P-256",prng);
    if (ecc.get_LastMethodSuccess() != true) {
        Log.i(TAG, ecc.lastErrorText());
        return;
        }

    String ecJwkStr = ecKey.getJwk();
    json.Load(ecJwkStr);
    Log.i(TAG, json.emit());

    // Sample EC JWK Key:
    // { 
    //   "kty": "EC",
    //   "crv": "P-256",
    //   "x": "tDeeYABgKEAbWicYPCEEI8sP4SRIhHKcHDW7VqrB4LA",
    //   "y": "J08HOoIZ0rX2Me3bNFZUltfxIk1Hrc8FsLu8VaSxsMI",
    //   "d": "-bqt1T0wNAN8sP5ruycQZRVlMlt3V_dSwlJ60xAX5io"
    // }

    // ----------------------------------------------
    // Octet sequence keys are intended for representing secret keys, such as HMAC keys and AES keys.

    // We'll use crypt to generate a random UUID..
    CkCrypt2 crypt = new CkCrypt2();

    // AES and HMAC keys are simply random arrays of bytes
    // For these, we can just build the JSON directly,
    // with the help of the PRNG object.

    CkJsonObject jwkHmac = new CkJsonObject();
    jwkHmac.put_EmitCompact(false);

    // Generate a 256-bit HMAK key (32 bytes)
    jwkHmac.AppendString("kty","oct");
    // Give the key an optional ID, which can be anything, even strings as simple as "1", "2", etc.
    jwkHmac.AppendString("kid",crypt.generateUuid());
    // Indicate the intended key alg (optional)
    jwkHmac.AppendString("alg","HS256");
    // Generate the actual key bytes
    jwkHmac.AppendString("k",prng.genRandom(32,"base64url"));

    Log.i(TAG, jwkHmac.emit());

    // Sample HMAC-256 JWK:

    // { 
    //   "kty": "oct",
    //   "kid": "06c2515d-41fb-e436-e405-3abb361f5f7a",
    //   "alg": "HS256",
    //   "k": "wR32w7yiMe5Lhb1vkW2koBpoMxpXTFYuxOYCCIEKjdE"
    // }

    // ----------------------------------------------
    // Now generate a 192-bit (24 byte) key that could be used with AES192GCM

    CkJsonObject jwkAes = new CkJsonObject();
    jwkAes.put_EmitCompact(false);

    jwkAes.AppendString("kty","oct");
    jwkAes.AppendString("kid","2");
    jwkAes.AppendString("k",prng.genRandom(24,"base64url"));

    Log.i(TAG, jwkAes.emit());

    // Sample AES key:
    // { 
    //   "kty": "oct",
    //   "kid": "2",
    //   "k": "akAkq-L_ZTZ6-tEIhDUMtU2ENhsEgL-p"
    // }

  }

  static {
      System.loadLibrary("chilkat");

      // Note: If the incorrect library name is passed to System.loadLibrary,
      // then you will see the following error message at application startup:
      //"The application <your-application-name> has stopped unexpectedly. Please try again."
  }
}