(Android™) JWE Using Flattened JWE JSON Serialization

This example duplicates the example A.5 in RFC 7516 for JSON Web Encryption (JWE).

This example demonstrates using the flattened JWE JSON Serialization syntax. This example demonstrates the capability for encrypting the plaintext to a single recipient in a flattened JSON structure.

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

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// 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.

    // Note: This example requires Chilkat v9.5.0.66 or greater.

    boolean success;
    String plaintext = "Live long and prosper.";

    CkJwe jwe = new CkJwe();

    // First build the JWE Protected Header: {"enc":"A128CBC-HS256"}
    CkJsonObject jweProtHdr = new CkJsonObject();
    jweProtHdr.AppendString("enc","A128CBC-HS256");
    jwe.SetProtectedHeader(jweProtHdr);

    // We have a single recipient that uses AES Key Wrap to encrypt the CEK.
    // 
    //      {"alg":"A128KW","kid":"7"}

    CkJsonObject jweRecipientHdr = new CkJsonObject();
    jweRecipientHdr.AppendString("alg","A128KW");
    jweRecipientHdr.AppendString("kid","7");
    int recipientIndex = 0;
    jwe.SetRecipientHeader(recipientIndex,jweRecipientHdr);

    // Set the Shared Unprotected Header:  {"jku":"https://server.example.com/keys.jwks"}
    CkJsonObject jweUnprotHdr = new CkJsonObject();
    jweUnprotHdr.AppendString("jku","https://server.example.com/keys.jwks");
    jwe.SetUnprotectedHeader(jweUnprotHdr);

    // Set the AES key wrapping key.
    String aesWrappingKey = "GawgguFyGrWKav7AX4VKUg";
    recipientIndex = 0;
    jwe.SetWrappingKey(recipientIndex,aesWrappingKey,"base64url");

    // OK.. everything has been specified.
    // Now encrypt.  
    // Indicate that we prefer the flattened JSON serialization.
    jwe.put_PreferFlattened(true);
    String strJwe = jwe.encrypt(plaintext,"utf-8");
    if (jwe.get_LastMethodSuccess() != true) {
        Log.i(TAG, jwe.lastErrorText());
        return;
        }

    // The JWE is produced in the most compact form possible (a single line).
    // Let's load it into a JSON object and examine in a non-compact pretty-printed format:
    CkJsonObject jsonTemp = new CkJsonObject();
    jsonTemp.Load(strJwe);
    jsonTemp.put_EmitCompact(false);
    Log.i(TAG, jsonTemp.emit());

    // The JWE looks like this:
    // (Note: Because of random values used in the encryption process, your encrypted results will be different.)

    // 	{ 
    // 	  "protected": "eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0",
    // 	  "unprotected": { 
    // 	    "jku": "https://server.example.com/keys.jwks"
    // 	  },
    // 	  "header": { 
    // 	    "alg": "A128KW",
    // 	    "kid": "7"
    // 	  },
    // 	  "encrypted_key": "FW7z9VxOvnF2ClicvUT4HTeqcdyh90C6qytfEFJsOb77FOwTfYrc3w",
    // 	  "iv": "O6Ly5-eML3zTs-_fNX3D5Q",
    // 	  "ciphertext": "Q8NLmeac9JhLh0CQPuG_7D9wVDb55eToCh0g5-FQ4M0",
    // 	  "tag": "slzlo6-J9C7wSDF4dh_kBg"
    // 	} 

    // Now decrypt......................................

    // First, load the JWE..
    CkJwe jwe2 = new CkJwe();
    success = jwe2.LoadJwe(strJwe);
    if (success != true) {
        Log.i(TAG, jwe2.lastErrorText());
        return;
        }

    // Set the AES wrap key..
    recipientIndex = 0;
    jwe2.SetWrappingKey(recipientIndex,aesWrappingKey,"base64url");

    // Decrypt
    String originalPlaintext = jwe2.decrypt(recipientIndex,"utf-8");
    if (jwe2.get_LastMethodSuccess() != true) {
        Log.i(TAG, jwe2.lastErrorText());
        return;
        }

    Log.i(TAG, "original text decrypted with AES key wrap key: ");
    Log.i(TAG, originalPlaintext);

    // ---------------------------------------------------------------------------------
    // It should also be possible to decrypt the flattened JWE as shown in RFC 7516, Appendix A.5
    // because it was produced using the same key.

    CkStringBuilder sbJwe = new CkStringBuilder();

    sbJwe.Append("{");
    sbJwe.Append("\"protected\":");
    sbJwe.Append("\"eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0\",");
    sbJwe.Append("\"unprotected\":");
    sbJwe.Append("{\"jku\":\"https://server.example.com/keys.jwks\"},");
    sbJwe.Append("\"header\":");
    sbJwe.Append("{\"alg\":\"A128KW\",\"kid\":\"7\"},");
    sbJwe.Append("\"encrypted_key\":");
    sbJwe.Append("\"6KB707dM9YTIgHtLvtgWQ8mKwboJW3of9locizkDTHzBC2IlrT1oOQ\",");
    sbJwe.Append("\"iv\":");
    sbJwe.Append("\"AxY8DCtDaGlsbGljb3RoZQ\",");
    sbJwe.Append("\"ciphertext\":");
    sbJwe.Append("\"KDlTtXchhZTGufMYmOYGS4HffxPSUrfmqCHXaI9wOGY\",");
    sbJwe.Append("\"tag\":");
    sbJwe.Append("\"Mz-VPPyU4RlcuYv1IwIvzw\"");
    sbJwe.Append("}");

    success = jwe2.LoadJweSb(sbJwe);
    if (success != true) {
        Log.i(TAG, jwe2.lastErrorText());
        return;
        }

    recipientIndex = 0;
    jwe2.SetWrappingKey(recipientIndex,aesWrappingKey,"base64url");

    originalPlaintext = jwe2.decrypt(recipientIndex,"utf-8");
    if (jwe2.get_LastMethodSuccess() != true) {
        Log.i(TAG, jwe2.lastErrorText());
        return;
        }

    Log.i(TAG, "original text decrypted from published flattened JWE: ");
    Log.i(TAG, originalPlaintext);

    // The output:

    // original text decrypted with AES key wrap key: 
    // Live long and prosper.
    // original text decrypted from published flattened JWE: 
    // Live long and prosper.

  }

  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."
  }
}