加密過程：以byte[]形式讀取SD卡上準備好的測試音訊檔案，使用AES加密演算法加密byte[]，再儲存覆蓋原音訊檔案，此時加密後的音訊檔案無法被播放。解密和加密過程原理一樣，解密儲存後的音訊檔案可以被播放。

程式碼：

VoiceEncryptionActivity.java

package com.example.voiceencryption;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.app.Activity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class VoiceEncryptionActivity extends Activity implements
		OnClickListener {
	private static final String TAG = "VoiceEncryptionActivity";
	private static final String seed = "guess"; // 種子
	private MediaPlayer mPlayer;
	private Button mPlayButton;
	private Button mEncryptionButton;
	private Button mDecryptionButton;
	private File sdCard = Environment.getExternalStorageDirectory();
	private File oldFile = new File(sdCard, "recording_old.3gpp");
	// 音訊檔案的路徑，在res\raw\recording_old.3gpp中找到音訊檔案，再放到外部儲存的根目錄下。用於測試
	private FileInputStream fis = null;
	private FileOutputStream fos = null;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_voice_encryption);
		mPlayButton = (Button) findViewById(R.id.playButton);
		mPlayButton.setOnClickListener(this);
		mEncryptionButton = (Button) findViewById(R.id.encryptionButton);
		mEncryptionButton.setOnClickListener(this);
		mDecryptionButton = (Button) findViewById(R.id.decryptionButton);
		mDecryptionButton.setOnClickListener(this);

	}

	@SuppressWarnings("static-access")
	@Override
	public void onClick(View v) {
		switch (v.getId()) {
		case R.id.playButton:
			if (mPlayer != null) {
				mPlayer.release();
				mPlayer = null;
			}
			// mPlayer = MediaPlayer.create(this, R.raw.recording_old);
			boolean isSuccess = true;
			try {
				fis = new FileInputStream(oldFile);
				mPlayer = new MediaPlayer();
				mPlayer.setDataSource(fis.getFD());
				mPlayer.prepare(); // 去掉會出錯
				mPlayer.start();
			} catch (FileNotFoundException e) {
				isSuccess = false;
				e.printStackTrace();
			} catch (IllegalArgumentException e) {
				isSuccess = false;
				e.printStackTrace();
			} catch (IllegalStateException e) {
				isSuccess = false;
				e.printStackTrace();
			} catch (IOException e) {
				isSuccess = false;
				e.printStackTrace();
			} finally {
				try {
					fis.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if (!isSuccess)
				Toast.makeText(this, "播放失敗", Toast.LENGTH_SHORT).show();
			break;

		case R.id.encryptionButton:
			// 加密儲存
			isSuccess = true;
			try {
				fis = new FileInputStream(oldFile);
				byte[] oldByte = new byte[(int) oldFile.length()];
				fis.read(oldByte); // 讀取
				byte[] newByte = AESUtils.encryptVoice(seed, oldByte);
				// 加密
				fos = new FileOutputStream(oldFile);
				fos.write(newByte);

			} catch (FileNotFoundException e) {
				isSuccess = false;
				e.printStackTrace();
			} catch (IOException e) {
				isSuccess = false;
				e.printStackTrace();
			} catch (Exception e) {
				isSuccess = false;
				e.printStackTrace();
			} finally {
				try {
					fis.close();
					fos.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			if (isSuccess)
				Toast.makeText(this, "加密成功", Toast.LENGTH_SHORT).show();
			else
				Toast.makeText(this, "加密失敗", Toast.LENGTH_SHORT).show();

			Log.i(TAG, "儲存成功");
			break;

		case R.id.decryptionButton:
			// 解密儲存
			isSuccess = true;
			byte[] oldByte = new byte[(int) oldFile.length()];
			try {
				fis = new FileInputStream(oldFile);
				fis.read(oldByte);
				byte[] newByte = AESUtils.decryptVoice(seed, oldByte);
				// 解密
				fos = new FileOutputStream(oldFile);
				fos.write(newByte);

			} catch (FileNotFoundException e) {
				isSuccess = false;
				e.printStackTrace();
			} catch (IOException e) {
				isSuccess = false;
				e.printStackTrace();
			} catch (Exception e) {
				isSuccess = false;
				e.printStackTrace();
			}
			try {
				fis.close();
				fos.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (isSuccess)
				Toast.makeText(this, "解密成功", Toast.LENGTH_SHORT).show();
			else
				Toast.makeText(this, "解密失敗", Toast.LENGTH_SHORT).show();
			break;

		default:
			break;
		}

	}
}
 

package com.example.voiceencryption;

import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class AESUtils {
	public static byte[] encryptVoice(String seed, byte[] clearbyte)
			throws Exception {
		byte[] rawKey = getRawKey(seed.getBytes());
		byte[] result = encrypt(rawKey, clearbyte);
		return result;
	}

	public static byte[] decryptVoice(String seed, byte[] encrypted)
			throws Exception {
		byte[] rawKey = getRawKey(seed.getBytes());
		byte[] result = decrypt(rawKey, encrypted);
		return result;
	}

	private static byte[] getRawKey(byte[] seed) throws Exception {
		KeyGenerator kgen = KeyGenerator.getInstance("AES");
		SecureRandom sr = SecureRandom.getInstance("SHA1PRNG", "Crypto");
		sr.setSeed(seed);
		kgen.init(128, sr);
		SecretKey skey = kgen.generateKey();
		byte[] raw = skey.getEncoded();
		return raw;
	}

	private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
		SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, skeySpec, new IvParameterSpec(
				new byte[cipher.getBlockSize()]));
		byte[] encrypted = cipher.doFinal(clear);
		return encrypted;
	}

	private static byte[] decrypt(byte[] raw, byte[] encrypted)
			throws Exception {
		SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.DECRYPT_MODE, skeySpec, new IvParameterSpec(
				new byte[cipher.getBlockSize()]));
		byte[] decrypted = cipher.doFinal(encrypted);
		return decrypted;
	}
}