问题
I'm using a simple CipherInput/OutputStream to try to encrypt/decrypt files in android.
The problem I'm having is that it seems to be corrupting the first few bytes of the file but not the rest. Here's an example of an output from a simple text file:
Original Text:
"Test for Android cipher. The quick brown fox jumps over the lazy dog."
Cycled through Encryption and Decryption:
@ÍØJb¢çc°ÌHOšpher. The quick brown fox jumps over the the lazy dog.
Here's my code:
public static SecretKey generateKey(Context c, char[] passphraseOrPin) throws NoSuchAlgorithmException, InvalidKeySpecException {
// Number of PBKDF2 hardening rounds to use. Larger values increase
// computation time. You should select a value that causes computation
// to take >100ms.
byte[] salt = Settings.Secure.getString(c.getContentResolver(),
Settings.Secure.ANDROID_ID).getBytes();
final int iterations = 1000;
final int outputKeyLength = 128;
SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec keySpec = new PBEKeySpec(passphraseOrPin, salt, iterations, outputKeyLength);
SecretKey secretKey = secretKeyFactory.generateSecret(keySpec);
Log.d("HIDEMYPICS","Secret Key: " + toHex(secretKey.getEncoded()) );
return secretKey;
}
public static boolean decryptFileFromUri(Context context, Uri file, String keyphrase) {
try {
File f = new File(getRealPathFromURI(context, file));
FileInputStream fis = new FileInputStream(f);
File ef = new File(f.toString().replace(".epf", ""));
FileOutputStream fos = new FileOutputStream(ef);
Log.d("HIDEMYPICS","Decrypting: " + f.toString());
SecretKey key = generateKey(context, keyphrase.toCharArray());
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, key);
// Wrap the output stream
CipherOutputStream cos = new CipherOutputStream(fos, cipher);
// Write bytes
int b;
byte[] d = new byte[8];
while ((b = fis.read(d)) != -1) {
cos.write(d, 0, b);
}
// Flush and close streams.
cos.flush();
cos.close();
fis.close();
Log.d("HIDEMYPICS","Decrypted to: " + ef.toString());
return true;
} catch (IOException e){
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (InvalidKeySpecException e) {
e.printStackTrace();
}
return false;
}
public static boolean encryptFileFromUri(Context context, Uri file, String keyphrase) {
try {
File f = new File(getRealPathFromURI(context, file));
FileInputStream fis = new FileInputStream(f);
File ef = new File(f.toString() + ".epf");
FileOutputStream fos = new FileOutputStream(ef);
Log.d("HIDEMYPICS","Encrypting: " + f.toString());
SecretKey key = generateKey(context, keyphrase.toCharArray());
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key);
// Wrap the output stream
CipherOutputStream cos = new CipherOutputStream(fos, cipher);
// Write bytes
int b;
byte[] d = new byte[8];
while ((b = fis.read(d)) != -1) {
cos.write(d, 0, b);
}
// Flush and close streams.
cos.flush();
cos.close();
fis.close();
Log.d("HIDEMYPICS","Encrypted to: " + ef.toString());
return true;
} catch (IOException e){
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (InvalidKeySpecException e) {
e.printStackTrace();
}
return false;
}
UPDATE:
Was advised to explicitly add a random IV to the cipher setup and added/modified the following lines of code to facilitate it:
SecureRandom r = new SecureRandom();
byte[] ivBytes = new byte[16];
r.nextBytes(ivBytes);
SecretKey key = generateKey(context, keyphrase.toCharArray());
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(ivBytes));
Ended up with the same result. First few bytes of the text file were still corrupted.
FINAL ANSWER:
Not sure what I did, but per suggestions below I had tried a static IV and it had still exhibited the same behavior, but I moved the declaration and something happened; probably had a typo somewhere. The issue is now resolved though and here's the final working code. Thanks all that helped out!
private static final byte[] ivBytes = {109,15,57,79,75,112,50,91,18,18,107,127,65,68,12,69};
public static SecretKey generateKey(Context c, char[] passphraseOrPin) throws NoSuchAlgorithmException, InvalidKeySpecException {
// Number of PBKDF2 hardening rounds to use. Larger values increase
// computation time. You should select a value that causes computation
// to take >100ms.
byte[] salt = Settings.Secure.getString(c.getContentResolver(),
Settings.Secure.ANDROID_ID).getBytes();
final int iterations = 1000;
final int outputKeyLength = 128;
SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec keySpec = new PBEKeySpec(passphraseOrPin, salt, iterations, outputKeyLength);
SecretKey secretKey = secretKeyFactory.generateSecret(keySpec);
return secretKey;
}
public static boolean decryptFileFromUri(Context context, Uri file, String keyphrase) {
try {
File f = new File(getRealPathFromURI(context, file));
FileInputStream fis = new FileInputStream(f);
File ef = new File(f.toString().replace(".epf", ""));
FileOutputStream fos = new FileOutputStream(ef);
SecretKey key = generateKey(context, keyphrase.toCharArray());
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(ivBytes));
// Wrap the output stream
CipherInputStream cis = new CipherInputStream(fis, cipher);
// Write bytes
int b;
byte[] d = new byte[8];
while ((b = cis.read(d)) != -1) {
fos.write(d, 0, b);
fos.flush();
}
// Flush and close streams.
fos.close();
cis.close();
f.delete();
return true;
} catch (IOException e){
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (InvalidKeySpecException e) {
e.printStackTrace();
} catch (InvalidAlgorithmParameterException e) {
e.printStackTrace();
}
return false;
}
public static boolean encryptFileFromUri(Context context, Uri file, String keyphrase) {
try {
File f = new File(getRealPathFromURI(context, file));
FileInputStream fis = new FileInputStream(f);
File ef = new File(f.toString() + ".epf");
FileOutputStream fos = new FileOutputStream(ef);
SecretKey key = generateKey(context, keyphrase.toCharArray());
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(ivBytes));
// Wrap the output stream
CipherOutputStream cos = new CipherOutputStream(fos, cipher);
// Write bytes
int b;
byte[] d = new byte[8];
while ((b = fis.read(d)) != -1) {
cos.write(d, 0, b);
cos.flush();
}
// Flush and close streams.
cos.close();
fis.close();
f.delete();
return true;
} catch (IOException e){
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (InvalidKeySpecException e) {
e.printStackTrace();
} catch (InvalidAlgorithmParameterException e) {
e.printStackTrace();
}
return false;
}
回答1:
Explicitly set a random IV and include it with your ciphertext.
来源：https://stackoverflow.com/questions/36680037/cipheroutputstream-corrupting-headers-in-android