Android™

Duplicate PHP's openssl_encrypt and openssl_random_pseudo_bytes

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Demonstrates how to duplicate PHP's openssl_encrypt function. (https://www.php.net/manual/en/function.openssl-encrypt.php) Android™

// 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);

    boolean success = false;

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

    // Duplicates thw following PHP script:

    // $text = "This is a test";
    // $passphrase = "my password";
    // $iv = openssl_random_pseudo_bytes(openssl_cipher_iv_length("AES-256-CBC"));
    // $crypted = base64_encode($iv.openssl_encrypt($text, "AES-256-CBC", $passphrase, OPENSSL_RAW_DATA, $iv));
    // echo $crypted;

    CkCrypt2 crypt = new CkCrypt2();

    String text = "This is a test";
    String passphrase = "my password";

    // AES is a block cipher.  The IV size for any block cipher is the size of the block, which is defined by the encryption algorithm. 
    // For AES, the block size is always 16 bytes, regardless of key size (i.e. 128-bits, 192-bits, or 256-bits).
    // Therefore, generate 16 random bytes for the IV.
    crypt.put_EncodingMode("base64");
    String ivBase64 = crypt.genRandomBytesENC(16);

    Log.i(TAG, "Generated IV = " + ivBase64);

    // Because we're doing AES-256-CBC, the key length must be 256-bits (i.e. 32 bytes).
    // Given that our passphrase is a us-ascii string that can be shorter or longer than 32-bytes, we need to 
    // somehow transform the passphrase to a 32-byte secret key.  We need to know what openssl_encrypt does.
    // Here's the answer from the openssl_encrypt documentation:
    // 
    // "If the passphrase is shorter than expected, it is silently padded with NUL characters; 
    // if the passphrase is longer than expected, it is silently truncated."

    // OK.... so let's pad or shorten to get a 32-byte key.
    CkBinData bdKey = new CkBinData();
    bdKey.AppendString(passphrase,"utf-8");

    int sz = bdKey.get_NumBytes();
    if (sz > 32) {
        bdKey.RemoveChunk(32,sz - 32);
        }
    else {
        bdKey.Clear();
        bdKey.AppendPadded(passphrase,"utf-8",false,32);
        }

    // Setup for encryption.
    crypt.put_CryptAlgorithm("aes");
    crypt.put_KeyLength(256);
    crypt.SetEncodedIV(ivBase64,"base64");
    crypt.SetEncodedKey(bdKey.getEncoded("base64"),"base64");

    // Encrypt and base64 encode.
    String cipherText64 = crypt.encryptStringENC(text);

    // The PHP code fragment above returns the base64 encoded bytes of the IV and the encrypted text.
    // So let's do that..
    CkBinData bd = new CkBinData();
    bd.AppendEncoded(ivBase64,"base64");
    bd.AppendEncoded(cipherText64,"base64");
    String result = bd.getEncoded("base64");

    Log.i(TAG, "result = " + result);

    // Sample output:
    // dN0vS1O0cWi5BbLAAY+NTf7bs3S27xzPf11RkG47sjs=

    // Now let's decrypt from the output...

    // Setup for decryption.
    crypt.put_CryptAlgorithm("aes");
    crypt.put_KeyLength(256);
    crypt.SetEncodedKey(bdKey.getEncoded("base64"),"base64");

    CkBinData bdResult = new CkBinData();
    bdResult.AppendEncoded(result,"base64");
    crypt.SetEncodedIV(bdResult.getEncodedChunk(0,16,"base64"),"base64");

    // Remove the IV (first 16 bytes) from the result.
    bdResult.RemoveChunk(0,16);
    success = crypt.DecryptBd(bdResult);
    String originalText = bdResult.getString("utf-8");

    Log.i(TAG, "original text = " + originalText);

  }

  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."
  }
}