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Android Java AES Encryption

I am currently making an Android app that includes encrypting a String with AES. But for some reason my app does not decrypt properly. I tried to change the Base64 format but it does not fix it. The code is similar to the example on Android Encryption with the Android Cryptography API
Does anyone know where did I go wrong with my functions? Since it does not decode to the same string as my encoded string ("pls").
Your help is much appreciated.
byte[] a = encryptFIN128AES("pls");
String b = decryptFIN128AES(a);
Log.e("AES_Test", "b = " + b);
/**
* Encrypts a string with AES (128 bit key)
* #param fin
* #return the AES encrypted byte[]
*/
private byte[] encryptFIN128AES(String fin) {
SecretKeySpec sks = null;
try {
sks = new SecretKeySpec(generateKey("Test1".toCharArray(), "Test2".getBytes()).getEncoded(),"AES");
} catch (Exception e) {
Log.e("encryptFIN128AES", "AES key generation error");
}
// Encode the original data with AES
byte[] encodedBytes = null;
try {
Cipher c = Cipher.getInstance("AES");
c.init(Cipher.ENCRYPT_MODE, sks);
encodedBytes = c.doFinal(fin.getBytes());
} catch (Exception e) {
Log.e("encryptFIN128AES", "AES encryption error");
}
return encodedBytes;
}
/**
* Decrypts a string with AES (128 bit key)
* #param encodedBytes
* #return the decrypted String
*/
private String decryptFIN128AES(byte[] encodedBytes) {
SecretKeySpec sks = null;
try {
sks = new SecretKeySpec(generateKey("Test1".toCharArray(), "Test2".getBytes()).getEncoded(),"AES");
} catch (Exception e) {
Log.e("decryptFIN128AES", "AES key generation error");
}
// Decode the encoded data with AES
byte[] decodedBytes = null;
try {
Cipher c = Cipher.getInstance("AES");
c.init(Cipher.DECRYPT_MODE, sks);
decodedBytes = c.doFinal(encodedBytes);
} catch (Exception e) {
Log.e("decryptFIN128AES", "AES decryption error");
}
return Base64.encodeToString(decodedBytes, Base64.DEFAULT);
}
public static SecretKey generateKey(char[] passphraseOrPin, byte[] salt)
throws NoSuchAlgorithmException, InvalidKeySpecException {
final int iterations = 1000;
// Generate a 256-bit key
final int outputKeyLength = 128;
SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec keySpec = new PBEKeySpec(passphraseOrPin, salt, iterations, outputKeyLength);
SecretKey secretKey = secretKeyFactory.generateSecret(keySpec);
return secretKey;
}
Output:
E/AES_Test: b = cGxz
**
[EDIT] Modified my code but now there is a NullPointerException
**
/**
* Encrypts a string with AES (128 bit key)
* #param fin
* #return the AES encrypted string
*/
private byte[] encryptFIN128AES(String fin) {
SecretKeySpec sks = null;
try {
sks = new SecretKeySpec(generateKey(PASSPHRASE, SALT.getBytes(StandardCharsets.UTF_8)).getEncoded(), "AES");
} catch (Exception e) {
Log.e("encryptFIN128AES", "AES key generation error");
}
// Encode the original data with AES
byte[] encodedBytes = null;
try {
Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");
c.init(Cipher.ENCRYPT_MODE, sks);
encodedBytes = c.doFinal(fin.getBytes(StandardCharsets.UTF_8));
} catch (Exception e) {
Log.e("encryptFIN128AES", "AES encryption error");
}
return encodedBytes;
}
/**
* Decrypts a string with AES (128 bit key)
* #param encodedBytes
* #return the decrypted String
*/
private String decryptFIN128AES(byte[] encodedBytes) {
SecretKeySpec sks = null;
try {
sks = new SecretKeySpec(generateKey(PASSPHRASE, SALT.getBytes(StandardCharsets.UTF_8)).getEncoded(), "AES");
} catch (Exception e) {
Log.e("decryptFIN128AES", "AES key generation error");
}
// Decode the encoded data with AES
byte[] decodedBytes = null;
try {
Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");
c.init(Cipher.DECRYPT_MODE, sks);
decodedBytes = c.doFinal(encodedBytes);
} catch (Exception e) {
Log.e("decryptFIN128AES", "AES decryption error");
}
//return Base64.encodeToString(decodedBytes, Base64.DEFAULT);
return new String(decodedBytes, StandardCharsets.UTF_8);
}
// generateKey(char[] passphraseOrPin, byte[] salt) remains the same
Error:
E/decryptFIN128AES: AES decryption error
E/AndroidRuntime: FATAL EXCEPTION: Thread-176
Process: testapp.ttyi.nfcapp, PID: 2920
java.lang.NullPointerException: Attempt to get length of null array
at java.lang.String.<init>(String.java:371)
at testapp.ttyi.nfcapp.DisplayQRActivity.decryptFIN128AES(DisplayQRActivity.java:254)
at testapp.ttyi.nfcapp.DisplayQRActivity.access$100(DisplayQRActivity.java:29)
at testapp.ttyi.nfcapp.DisplayQRActivity$1.run(DisplayQRActivity.java:77)
at java.lang.Thread.run(Thread.java:818)
**
[EDIT2] Resolved (But no Padding/Encryption Mode allowed)
**
I managed to resolve the issue. (Decodes to "pls") using Codo's solution ofreturn new String(decodedBytes, StandardCharsets.UTF_8);
Though it only works when the algorithm used is:
Cipher c = Cipher.getInstance("AES");
When I put Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");
The "NullPointerException" as seen above will happen. My observation shows that during decryption:
try {
Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");
c.init(Cipher.DECRYPT_MODE, sks);
decodedBytes = c.doFinal(encodedBytes);
} catch (Exception e) {
Log.e("decryptFIN128AES", "AES decryption error");
}
something will fail and it will always print out:
E/decryptFIN128AES: AES decryption error
And thus the NullPointerException will occur as decodedBytes is always initiated to NULL.

Your process is not balanced. For encryption you do:
Encode string using default charset (fin.getBytes()) to get binary data
Encrypt binary data to get encrypted data (doFinal)
For the decryption, you do:
Decrypt encrypted data to get unencrypted binary data (doFinal)
Encode binary data as a Base64 string
Instead of Base64 encoding, the last step should be the reverse of step 1 in the encryption, i.e. you should decode the binary data into a string:
return String(decodedBytes);
It strongly recommend, you do not use the default charset for encoding and decoding as it depends on the system's setting. So it could be different between the system where you encrypt and decyrpt.
So use:
fin.getBytes(StandardCharsets.UTF_8);
and:
return String(decodedBytes, StandardCharsets.UTF_8);
The same applies for the salt.
Also note that you should specify the padding and chaining mode. If you don't, provider-specific default values apply. See #Ryan's answer for more details.

You should research more on how to use AES correctly as you are missing some basic fundamentals of AES security: no IV (assuming using CBC), no mode specified (such as CBC), and no padding specified (such as PKCS5).

Looks like char encoding issue. With minor modifications it works.
in encryptFIN128AES:
encodedBytes = c.doFinal(Base64.getEncoder().encode(fin.getBytes()));
in decryptFIN128AES:
return new String(Base64.getDecoder().decode(decodedBytes));

How to decrypt an encrypted AES file using base64 Symmetric key and IV

I have been given an encrypted file along with a base64 symmetric key and base 64 IV and have been asked to decrypt it using Java. The encryption used on the data file was AES. However, when I run the encrypted file, symmetric key and IV into my code, I get the following error:
javax.crypto.IllegalBlockSizeException: Input length must be multiple of 16 when decrypting with padded cipher
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:913)
Here is my code:
String encryptedData = "C:\\EncryptedDataFile.data";
FileInputStream fis = null;
File file = new File(encryptedData);
//Convert file into array of bytes
byte[] encryptedDataBytes = new byte[(int) file.length()];
try
{
// Read in array of bytes
fis = new FileInputStream(file);
fis.read(encryptedDataBytes);
fis.close();
}
catch (FileNotFoundException ex)
{
ex.printStackTrace();
}
catch (IOException ex)
{
ex.printStackTrace();
}
// AES Key
byte[] decodedKey = Base64.getDecoder().decode("50rofsdb0TnQAQCb702wKz8m6XQeLNj6lamEvivKsh8=");
// decode the base64 encoded string
SecretKey originalKey = new SecretKeySpec(decodedKey, 0, decodedKey.length, "AES"); // rebuild key using SecretKeySpec
// IV
byte[] initVecBytes = Base64.getDecoder().decode("OUXLZq4SpyhzNGIei0nerA==");
// Decrypt the cipher text
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
IvParameterSpec ivParameterSpec = new IvParameterSpec(initVecBytes);
cipher.init(Cipher.DECRYPT_MODE, originalKey, ivParameterSpec);
byte[] original = cipher.doFinal(encryptedDataBytes);
String s = new String(original);
System.out.println(s);
If someone could provide some help to me on this matter it would be much appreciated

AES encryption, got extra trash characters in decrypted file

Im making a debug loggin function in an android app.
I have a simple class which is logging to .txt file using 128 bit AES encryption.
After the logging is done, i decrypt the logged file with a simple JAVA program.
The problem is when i decrypt the encrypted log i got some weird content in it, i also got the encrypted content, but there are some extra characters, see below.
Android app logging part:
public class FileLogger {
//file and folder name
public static String LOG_FILE_NAME = "my_log.txt";
public static String LOG_FOLDER_NAME = "my_log_folder";
static SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd_HH-mm-ss_SSS");
//My secret key, 16 bytes = 128 bit
static byte[] key = {1,2,3,4,5,6,7,8,9,0,1,2,3,4,5,6};
//Appends to a log file, using encryption
public static void appendToLog(Context context, Object msg) {
String msgStr;
String timestamp = "t:" + formatter.format(new java.util.Date());
msgStr = msg + "|" + timestamp + "\n";
File sdcard = Environment.getExternalStorageDirectory();
File dir = new File(sdcard.getAbsolutePath() + "/" + LOG_FOLDER_NAME);
if (!dir.exists()) {
dir.mkdir();
}
File encryptedFile = new File(dir, LOG_FILE_NAME);
try {
//Encryption using my key above defined
Key secretKey = new SecretKeySpec(key, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.ENCRYPT_MODE, secretKey);
byte[] outputBytes = cipher.doFinal(msgStr.getBytes());
//Writing to the file using append mode
FileOutputStream outputStream = new FileOutputStream(encryptedFile, true);
outputStream.write(outputBytes);
outputStream.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (IllegalBlockSizeException e) {
e.printStackTrace();
} catch (BadPaddingException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
}
}
}
And this is the decrypter JAVA program:
public class Main {
//output file name after decryption
private static String decryptedFileName;
//input encrypted file
private static String fileSource;
//a prefix tag for output file name
private static String outputFilePrefix = "decrypted_";
//My key for decryption, its the same as in the encrypter program.
static byte[] key = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6 };
//Decrypting function
public static void decrypt(byte[] key, File inputFile, File outputFile) throws Exception {
try {
Key secretKey = new SecretKeySpec(key, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, secretKey);
FileInputStream inputStream = new FileInputStream(inputFile);
byte[] inputBytes = new byte[(int) inputFile.length()];
inputStream.read(inputBytes);
byte[] outputBytes = cipher.doFinal(inputBytes);
FileOutputStream outputStream = new FileOutputStream(outputFile, true);
outputStream.write(outputBytes);
inputStream.close();
outputStream.close();
} catch (Exception ex) {
ex.printStackTrace();
}
}
//first argument is the intput file source
public static void main(String[] args) {
if (args.length != 1) {
System.out.println("Add log file name as a parameter.");
} else {
fileSource = args[0];
try {
File sourceFile = new File(fileSource);
if (sourceFile.exists()) {
//Decrption
decryptedFileName = outputFilePrefix + sourceFile.getName();
File decryptedFile = new File(decryptedFileName);
decrypt(key, sourceFile, decryptedFile);
} else {
System.out.println("Log file not found: " + fileSource);
}
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("Decryption done, output file: " + decryptedFileName);
}
}
}
Output decrypted log (Opened with notepad++):
There is the valid content, but you also can see the extra thrash characters. If I open with the default windows text editor i also got thrash charaters, but different ones.
This is my first try with encrypt -decrypt, what m i doing wrong?
Any ideas?

AES is a block cipher which only works on blocks. The plaintext that you want to encrypt can be of any length, so the cipher must always pad the plaintext to fill it up to a multiple of the block size (or add a complete block when it already is a multiple of the block size). In this PKCS#5/PKCS#7 padding each padding byte denotes the number of padded bytes.
The easy fix would be to iterate over outputBytes during decryption and remove those padding bytes which are always on the next line. This will break as soon as you use multiline log messages or use a semantically secure mode (more on that later).
The better fix would be to write the number of bytes for each log message before the message, read that and decrypt only that many bytes. This also probably easier to implement with file streams.
You currently use Cipher.getInstance("AES"); which is a non-fully qualified version of Cipher.getInstance("AES/ECB/PKCS5Padding");. ECB mode is not semantically secure. It simply encrypts each block (16 bytes) with AES and the key. So blocks that are the same will be the same in ciphertext. This is particularly bad, because some log messages start the same and an attacker might be able to distinguish them. This is also the reason why the decryption of the whole file worked despite being encrypted in chunks. You should use CBC mode with a random IV.
Here is some sample code for proper use of AES in CBC mode with a random IV using streams:
private static SecretKey key = generateAESkey();
private static String cipherString = "AES/CBC/PKCS5Padding";
public static void main(String[] args) throws Exception {
ByteArrayOutputStream log = new ByteArrayOutputStream();
appendToLog("Test1", log);
appendToLog("Test2 is longer", log);
appendToLog("Test3 is multiple of block size!", log);
appendToLog("Test4 is shorter.", log);
byte[] encLog = log.toByteArray();
List<String> logs = decryptLog(new ByteArrayInputStream(encLog));
for(String logLine : logs) {
System.out.println(logLine);
}
}
private static SecretKey generateAESkey() {
try {
return KeyGenerator.getInstance("AES").generateKey();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return null;
}
private static byte[] generateIV() {
SecureRandom random = new SecureRandom();
byte[] iv = new byte[16];
random.nextBytes(iv);
return iv;
}
public static void appendToLog(String s, OutputStream os) throws Exception {
Cipher cipher = Cipher.getInstance(cipherString);
byte[] iv = generateIV();
cipher.init(Cipher.ENCRYPT_MODE, key, new IvParameterSpec(iv));
byte[] data = cipher.doFinal(s.getBytes("UTF-8"));
os.write(data.length);
os.write(iv);
os.write(data);
}
public static List<String> decryptLog(InputStream is) throws Exception{
ArrayList<String> logs = new ArrayList<String>();
while(is.available() > 0) {
int len = is.read();
byte[] encLogLine = new byte[len];
byte[] iv = new byte[16];
is.read(iv);
is.read(encLogLine);
Cipher cipher = Cipher.getInstance(cipherString);
cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
byte[] data = cipher.doFinal(encLogLine);
logs.add(new String(data, "UTF-8"));
}
return logs;
}

You've encrypted each log message with a distinct encryption context. When you call the doFinal method on the cipher object the plaintext is padded out to a multiple of 16. Effectively, your log file is sequence of many small encrypted messages. However on decryption you are ignoring these message boundaries and treating the file as a single encrypted message. The result is that the padding characters are not being properly stripped. What you are seeing as 'trash' characters are likely these padding bytes. You will need to redesign your logfile format, either to preserve the message boundaries so the decryptor can discover them or to eliminate them altogether.
Also, don't use defaults in Java cryptography: they're not portable. For example, Cipher.getInstance() takes a string of the form alg/mode/padding. Always specify all three. I notice you also use the default no-args String.getBytes() method. Always specify a Charset, and almost always "UTF8" is the best choice.

Android exception java.io.IOException: last block incomplete

I am working on decrypting a binary file encrypted in C# using Rijndael encryption method. The file is copied to an android device. The decryption logic works fine when run in a java based desktop test program. But it throws java.io.IOException: last block incomplete when run in android. I am using the code below.
public static void Decrypt(String fileIn, String fileOut, byte[] key, byte[] IV, long offset)
{
// First we are going to open the file streams
FileInputStream fsIn;
try
{
fsIn = new FileInputStream(fileIn);,,
FileOutputStream fsOut = new FileOutputStream(fileOut);
// create cipher object
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"), new IvParameterSpec(IV));
// create the encryption stream
CipherInputStream cis = new CipherInputStream(fsIn, cipher);
// set a buffer and keep writing to the stream
int bufferLen = KiloByte;
byte[] buffer = new byte[bufferLen];
int bytesRead = 0;
// read a chunk of data from the input file
while ( (bytesRead = cis.read(buffer, 0, bufferLen)) != -1)
{
// write to file
fsOut.write(buffer, 0, bytesRead);
}
fsOut.flush();
// close streams
fsOut.close();
cis.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (NoSuchPaddingException e) {
e.printStackTrace();
} catch (InvalidKeyException e) {
e.printStackTrace();
} catch (InvalidAlgorithmParameterException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
The key is generated by using the function
public static byte[] GetKey(String password, byte[] IV, int length)
throws NoSuchAlgorithmException, InvalidKeySpecException
{
// Length is kept 16 to make it compatible with all platforms
SecretKeyFactory f = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec ks = new PBEKeySpec(password.toCharArray(), IV, 1000, length*8);
SecretKey s = f.generateSecret(ks);
Key k = new SecretKeySpec(s.getEncoded(),"AES");
return k.getEncoded();
}
I have gone through many posts on internet related to the topic. Based on that, I have made sure that I use byte array rather String. But still getting this issue.

Java AES PKCS7 - last block incomplete in decryption

I have an Python application that creates a few files encrypted with AES/PKCS7. I have to read those files with a Java service. But my code is throwing an exception:
"javax.crypto.IllegalBlockSizeException: last block incomplete in decryption"
Here's my decryption code:
public String Decrypt(String strText)
{
try
{
// Text to decrypt
byte[] test = strText.getBytes();
//bytKey is the same key as Python app
SecretKeySpec objKey = new SecretKeySpec(bytKey, "AES");
Cipher objCipher = Cipher.getInstance("AES/ECB/PKCS7Padding", "BC");
objCipher.init(Cipher.DECRYPT_MODE, objKey);
// Here I got an exception >>
byte[] bytValue = objCipher.doFinal(test);
return new String(bytValue);
}
catch (Exception exc)
{
exc.printStackTrace();
}
return "";
}
If I decode the encrypted text before step into doFinal I get another exception:
"javax.crypto.BadPaddingException: pad block corrupted"
public String Decrypt(String strText)
{
try
{
BASE64Decoder decoder = new BASE64Decoder();
byte[] test = decoder.decodeBuffer(strText);
SecretKeySpec objKey = new SecretKeySpec(bytKey, "AES");
Cipher objCipher = Cipher.getInstance("AES/ECB/PKCS7Padding", "BC");
objCipher.init(Cipher.DECRYPT_MODE, objKey);
byte[] bytValue = objCipher.doFinal(test);
return new String(bytValue);
}
catch (Exception exc)
{
exc.printStackTrace();
}
return "";
}
I'm not an expert on encrypt/decrypt and I guess it's quite simple to solve.
Any ideas to solve this issue? Thanks in advance!