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Problem with ANSI Encoding file with Encryption in Linux, Java

I export a database with mysqldump a database in Ubuntu with java, then I encrypt and decrypt it with Java. I doing that with the following classes Encrypt and Decrypt with Java. But after the decryption some characters at the start of the file is wrong. Here is the problem:
At the first image is the file which programmatically have mysqldump, encrypt and decrypt. At the second one is just the mysqldump from the same command line. Can you point me the direction what to do? Thanks
EDIT
I have create a salt and stored it in a file like this:
Encryption:
FileInputStream saltFis = new FileInputStream("salt.enc");
byte[] salt = new byte[8];
saltFis.read(salt);
saltFis.close();
// reading the iv
FileInputStream ivFis = new FileInputStream("iv.enc");
byte[] iv = new byte[16];
ivFis.read(iv);
ivFis.close();
SecretKeyFactory factory = SecretKeyFactory.getInstance(secretAlgorithm1);
KeySpec keySpec = new PBEKeySpec(rsaSecret.toCharArray(), salt, 65536, 256);
SecretKey secretKey = factory.generateSecret(keySpec);
SecretKey secret = new SecretKeySpec(secretKey.getEncoded(), secretAlgorithm2);
//
Cipher cipher = Cipher.getInstance(algorithmEncryption);
cipher.init(Cipher.ENCRYPT_MODE, secret);
// file encryption
byte[] input = new byte[64];
int bytesRead;
while ((bytesRead = inFile.read(input)) != -1) {
byte[] output = cipher.update(input, 0, bytesRead);
if (output != null)
outFile.write(output);
}
byte[] output = cipher.doFinal();
if (output != null)
outFile.write(output);
inFile.close();
outFile.flush();
outFile.close();
Decryption:
FileInputStream saltFis = new FileInputStream("salt.enc");
byte[] salt = new byte[8];
saltFis.read(salt);
saltFis.close();
// reading the iv
FileInputStream ivFis = new FileInputStream("iv.enc");
byte[] iv = new byte[16];
ivFis.read(iv);
ivFis.close();
SecretKeyFactory factory = SecretKeyFactory.getInstance(secretAlgorithm1);
KeySpec keySpec = new PBEKeySpec(rsaSecret.toCharArray(), salt, 65536, 256);
SecretKey secretKey = factory.generateSecret(keySpec);
SecretKey secret = new SecretKeySpec(secretKey.getEncoded(), secretAlgorithm2);
// file decryption
Cipher cipher = Cipher.getInstance(algorithmEncryption);
cipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iv));
FileInputStream fis = new FileInputStream(decodedB64);
FileOutputStream fos = new FileOutputStream(outputFile);
byte[] in = new byte[64];
int read;
while ((read = fis.read(in)) != -1) {
byte[] output = cipher.update(in, 0, read);
if (output != null)
fos.write(output);
}
byte[] output = cipher.doFinal();
if (output != null)
fos.write(output);
fis.close();
fos.flush();
fos.close();
System.out.println("File Decrypted.");

Oh, that one is simple. That idiotic (but funny enough, seeming largely correct otherwise) method of file encryption using CBC stores the IV in a separate file, overwriting any old one. So if you overwrite or take the wrong IV file then you'll get 16 random bytes at the start after decryption. So unless you can find the IV file that hopefully makes sense, your first 16 bytes (/characters) are now lost forever.
Of course, any sane encryption program stores the salt (a password & PBKDF2 is used for key derivation) and IV in the same file as the ciphertext.
Still, if you managed to lose the salt file or password then all the data would have been lost, so there's that...
With the added code the issue becomes even more clear. In the encryption mode you are forgetting to create & use an IvParameterSpec entirely during initialization:
cipher.init(Cipher.ENCRYPT_MODE, secret);
however, because of the way the IV data is read, you don't get any warning that the variable isn't used:
ivFis.read(iv);
If you would have created a nice method such as IvParameterSpec iv = readIvFromFile() then you would have caught this error.
Note that Java (by default in the included provider for Cipher) uses an all zero IV, so you're lucky and your data isn't partially gone.

Need help implementing CipherInputStream and CipherOutputStream [duplicate]

This question already has answers here:
Initial bytes incorrect after Java AES/CBC decryption
(10 answers)
Closed 3 years ago.
I'm having some issues converting FileInputStream and FileOutputStream into CipherInputStream and CipherOutputStream for my 3DES encryption algorithm. Could someone direct me on the right path on how to do it? I end up getting the error: "CipherInputStream cannot be resolved to a type". Sorry if this is obvious.
// author Alexander Matheakis
public static void main(String[] args) throws Exception {
// file to be encrypted
FileInputStream inputFile = new FileInputStream("plainfile.txt");
// encrypted file
FileOutputStream outputFile = new FileOutputStream("C:\\Users\\islan\\OneDrive\\Documents\\Encryptor\\plainfile.des");
// password to encrypt the file
String passKey = "tkfhkggovubm";
byte[] salt = new byte[8];
SecureRandom r = new SecureRandom();
r.nextBytes(salt);
PBEKeySpec pbeKeySpec = new PBEKeySpec(passKey.toCharArray());
SecretKeyFactory secretKeyFactory = SecretKeyFactory
.getInstance("PBEWithSHA1AndDESede");
SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);
PBEParameterSpec pbeParameterSpec = new PBEParameterSpec(salt, 99999);
Cipher cipher = Cipher.getInstance("PBEWithSHA1AndDESede");
cipher.init(Cipher.ENCRYPT_MODE, secretKey, pbeParameterSpec);
outputFile.write(salt);
byte[] input = new byte[64];
int bytesRead;
while ((bytesRead = inputFile.read(input)) != -1) {
byte[] output = cipher.update(input, 0, bytesRead);
if (output != null)
outputFile.write(output);
}
byte[] output = cipher.doFinal();
if (output != null)
outputFile.write(output);
inputFile.close();
outputFile.flush();
outputFile.close();
// author Alexander Matheakis

This works for me:
public class Cypher {
// password to encrypt the file
private static final String passKey = "tkfhkggovubm";
public static void main(String[] args) throws Exception {
try (FileInputStream inputFile = new FileInputStream("plainfile.txt");
FileOutputStream outputFile = new FileOutputStream("plainfile.des");) {
byte[] salt = new byte[8];
SecureRandom r = new SecureRandom();
r.nextBytes(salt);
outputFile.write(salt);
PBEKeySpec pbeKeySpec = new PBEKeySpec(passKey.toCharArray());
SecretKeyFactory secretKeyFactory = SecretKeyFactory
.getInstance("PBEWithSHA1AndDESede");
SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);
PBEParameterSpec pbeParameterSpec = new PBEParameterSpec(salt, 99999);
Cipher cipher = Cipher.getInstance("PBEWithSHA1AndDESede");
cipher.init(Cipher.ENCRYPT_MODE, secretKey, pbeParameterSpec);
try (CipherOutputStream cis = new CipherOutputStream(outputFile, cipher);) {
IOUtils.copy(inputFile, cis);
}
}
try (FileInputStream fis = new FileInputStream("plainfile.des");
FileOutputStream outputFile = new FileOutputStream("plainfile.txt2");) {
byte[] salt = new byte[8];
int saltBytes = fis.read(salt);
if (saltBytes!=salt.length)
throw new Exception("Huh???");
PBEKeySpec pbeKeySpec = new PBEKeySpec(passKey.toCharArray());
SecretKeyFactory secretKeyFactory = SecretKeyFactory
.getInstance("PBEWithSHA1AndDESede");
SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);
PBEParameterSpec pbeParameterSpec = new PBEParameterSpec(salt, 99999);
Cipher cipher = Cipher.getInstance("PBEWithSHA1AndDESede");
cipher.init(Cipher.DECRYPT_MODE, secretKey, pbeParameterSpec);
try (CipherInputStream cis = new CipherInputStream(fis, cipher);) {
IOUtils.copy(cis, outputFile);
}
}
}
}
After executing the main, the plainfile.txt and the plainfile.txt2 are equal. The plainfile.des is crypted.
IOUtils.copy is a method in apache.commons-io, which internally reserves a buffer and writes all bytes from one stream to another.
It's just the byte[] input = ... extracted into a method, plus using try-with-resources.
This keeps the code simple and better readable.

How to handle BadPaddingException During AES256 encryption in C# and decryption in Java

I don't know why an error is coming up.
Exception in thread "main" javax.crypto.BadPaddingException: Given final block not properly padded. Such issues can arise if a bad key is used during decryption.
I understand that this error occurs when the incorrect key is used during the decryption. However, if you look at the test results result below, you can see that both C# and Java are the same (Key, IV, Salt is Base64 encoded).
C# Test Result
Java Test Result
It's the same!(Key, IV, Salt)
But the current BadpaddingException error is generated. What could be the problem?
I am attaching my source file.
C# (Encryption)
class AES {
private readonly static string keyStr = "This is Key";
private readonly static string vector = "This is Vector";
public static Rfc2898DeriveBytes MakeKey(string password){
byte[] keyBytes = System.Text.Encoding.UTF8.GetBytes(password);
byte[] saltBytes = SHA512.Create().ComputeHash(keyBytes);
Rfc2898DeriveBytes result = new Rfc2898DeriveBytes(keyBytes, saltBytes, 65536);
return result;
}
public static Rfc2898DeriveBytes MakeVector(string vector){
byte[] vectorBytes = System.Text.Encoding.UTF8.GetBytes(vector);
byte[] saltBytes = SHA512.Create().ComputeHash(vectorBytes);
Rfc2898DeriveBytes result = new Rfc2898DeriveBytes(vectorBytes, saltBytes, 65536);
return result;
}
public static void Encrypt(String inputFile, String outputFile) {
using (RijndaelManaged aes = new RijndaelManaged()){
//Create Key and Vector
Rfc2898DeriveBytes key = AES.MakeKey(AES.keyStr);
Rfc2898DeriveBytes vector = AES.MakeVector(AES.vector);
//AES256
aes.BlockSize = 128;
aes.KeySize = 256;
// It is equal in java
// Cipher _Cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING");
aes.Mode = CipherMode.CBC;
aes.Padding = PaddingMode.PKCS7;
aes.Key = key.GetBytes(32); //256bit key
aes.IV = vector.GetBytes(16); //128bit block size
//processing Encrypt
ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
byte[] encrypted;
using (MemoryStream msEncrypt = new MemoryStream()) {
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write)) {
byte[] inputBytes = File.ReadAllBytes(inputFile);
csEncrypt.Write(inputBytes, 0, inputBytes.Length);
}
encrypted = msEncrypt.ToArray();
}
string encodedString = Convert.ToBase64String(encrypted);
File.WriteAllText(outputFile, encodedString);
}
}
}
Java (Decryption)
public class AES256File {
private static final String algorithm = "AES";
private static final String blockNPadding = algorithm+"/CBC/PKCS5Padding";
private static final String password = "This is Key";
private static final String IV = "This is Vector";
private static IvParameterSpec ivSpec;
private static Key keySpec;
public static void MakeKey(String password) throws NoSuchAlgorithmException, UnsupportedEncodingException, InvalidKeySpecException{
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
MessageDigest digest = MessageDigest.getInstance("SHA-512");
byte[] keyBytes = password.getBytes("UTF-8");
// C# : byte[] saltBytes = SHA512.Create().ComputeHash(keyBytes);
byte[] saltBytes = digest.digest(keyBytes);
//256bit
PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray(), saltBytes, 65536, 256);
Key secretKey = factory.generateSecret(pbeKeySpec);
byte[] key = new byte[32];
System.arraycopy(secretKey.getEncoded(), 0, key, 0, 32);
SecretKeySpec secret = new SecretKeySpec(key, "AES");
setKeySpec(secret);
}
public static void MakeVector(String IV) throws NoSuchAlgorithmException, UnsupportedEncodingException, InvalidKeySpecException{
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
MessageDigest digest = MessageDigest.getInstance("SHA-512");
byte[] vectorBytes = IV.getBytes("UTF-8");
byte[] saltBytes = digest.digest(vectorBytes);
// 128bit
PBEKeySpec pbeKeySpec = new PBEKeySpec(IV.toCharArray(), saltBytes, 65536, 128);
Key secretIV = factory.generateSecret(pbeKeySpec);
byte[] iv = new byte[16];
System.arraycopy(secretIV.getEncoded(), 0, iv, 0, 16);
IvParameterSpec ivSpec = new IvParameterSpec(iv);
setIvSpec(ivSpec);
}
public void decrypt(File source, File dest) throws Exception {
Cipher c = Cipher.getInstance(blockNPadding);
c.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
fileProcessing(source, dest, c);
}
public void fileProcessing(File source, File dest, Cipher c) throws Exception{
InputStream input = null;
OutputStream output = null;
try{
input = new BufferedInputStream(new FileInputStream(source));
output = new BufferedOutputStream(new FileOutputStream(dest));
byte[] buffer = new byte[input.available()];
int read = -1;
while((read = input.read(buffer)) != -1){
output.write(c.update(buffer, 0, read));
}
byte[] deryptedBytes = c.doFinal(buffer); // -----------------------> Error!! Showing!
byte[] decodedBytes = Base64.getDecoder().decode(deryptedBytes);
String decodeString = new String(decodedBytes, "UTF-8");
decodedBytes = decodeString.getBytes(StandardCharsets.UTF_8);
output.write(decodedBytes);
}finally{
if(output != null){
try{output.close();}catch(IOException e){}
}
if(input != null){
try{input.close();}catch(IOException e){}
}
}
}
I have verified as below.
Verification Key and IV in C#
//Key Verification
var salt = Convert.ToBase64String(saltBytes);
Console.Write("Salt Result : ");
Console.WriteLine(salt);
var result_test = Convert.ToBase64String(result.GetBytes(32));
Console.Write("Key Test Result: ");
Console.WriteLine(result_test);
//IV Verification (Salt is Using same code)
var result_test = Convert.ToBase64String(result.GetBytes(16));
Console.Write("IV Test Result: ");
Console.WriteLine(result_test);
Verification Key and IV in Java
//Key Verification
/* print Salt */
String base64 = Base64.getEncoder().encodeToString(saltBytes);
System.out.println("Salt Result : " + base64);
/* print Key */
String result_test = Base64.getEncoder().encodeToString(key);
System.out.println("Key Test Result : " + result_test);
/* print generated Key */
System.out.println("Secret Key Result : " + Base64.getEncoder().encodeToString(secret.getEncoded()));
//IV Verification (Salt is Using same code)
/* print IV */
String result_test = Base64.getEncoder().encodeToString(iv);
System.out.println("IV Test Result : " + result_test);
/* print generated IV */
System.out.println("IV Result : " + Base64.getEncoder().encodeToString(ivSpec.getIV()));
Updated
c# .netframework 4.5 / Java8 modified what #Topaco said and confirmed that it worked well.
I want to say thank you very much to #Topaco and #Gusto2, and I'm going to make changes to the parts that have been modified in security, just as #Gusto2 said!

1) In the C# Encrypt-method the plain text is encrypted first and then Base64-encoded. Thus, in the decryption process the data must be Base64-decoded first and then decrypted. Currently this is handled in the wrong order i.e. the data are decrypted first and then decoded. Therefore, in the Java fileProcessing-method replace
while((read = input.read(buffer)) != -1){
output.write(c.update(buffer, 0, read));
}
with
while((read = input.read(buffer)) != -1) {
byte[] bufferEncoded = buffer;
if (read != buffer.length) {
bufferEncoded = Arrays.copyOf(buffer, read);
}
byte[] bufferDecoded = Base64.getDecoder().decode(bufferEncoded);
output.write(c.update(bufferDecoded));
}
2) It's not necessary to pass buffer (or bufferDecoded) to the doFinal-method, since that was already done in the update-method. Thus,
byte[] deryptedBytes = c.doFinal(buffer);
must be replaced with
output.write(c.doFinal());
3) Since the Base64-decoding is already done in 1) in the try-block all lines following the doFinal-statement have to be removed. Overall, this results in
try {
input = new BufferedInputStream(new FileInputStream(source));
output = new BufferedOutputStream(new FileOutputStream(dest));
byte[] buffer = new byte[input.available()];
int read = -1;
while((read = input.read(buffer)) != -1) {
byte[] bufferEncoded = buffer;
if (read != buffer.length) {
bufferEncoded = Arrays.copyOf(buffer, read);
}
byte[] bufferDecoded = Base64.getDecoder().decode(bufferEncoded);
output.write(c.update(bufferDecoded));
}
output.write(c.doFinal());
}
4) The size of the buffer has to be a multiple of 4 in order to ensure a proper Base64-decoding. Thus, it's more reliable to replace
byte[] buffer = new byte[input.available()];
with
byte[] buffer = new byte[4 * (input.available() / 4)];
As long as the data are read in one chunk (which is not guaranteed, see e.g. https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/InputStream.html#available()) there is no problem. However, if the data are read in several chunks it's important to read a multiple of 4 bytes, otherwise the Base64-decoding will fail. That can be easily proved by using a buffer size which isn't a multiple of 4. This point must also be considered if the buffer size is explicitly defined with regard to larger files.

while((read = input.read(buffer)) != -1){
output.write(c.update(buffer, 0, read));
}
byte[] deryptedBytes = c.doFinal(buffer)
you are decrypting the input to a file, then you are using the same cipher instance to decrypt the the last read chunk (again) into a separate array not to the file
quick fix:
while((read = input.read(buffer)) != -1){
output.write(c.update(buffer, 0, read));
}
output.write(c.doFinal()); // write the padded block
if you want to create and print a decrypted String, you need to create a new Cipher instance (or maybe it will be enough to reinitialize the instance, I am not sure) assuming the buffer contains the whole input
c.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
// assuming the buffer contains the whole input again
byte[] deryptedBytes = c.doFinal(buffer); // decrypting the whole file again
correct approach:
IV is used to securely reuse the same encryption key for multiple encryptions. So if your key is not random, you should generate new random IV for each encryption (and pass the IV along the ciphertext, most often prepended). Otherwise the encryption is not semantically secure and you may create opening for the two pad attack. So deriving IV from the key may not be very secure.
I advice to use any MAC (authentication code) passed along the ciphertext to ensure integrity (e.g. HMAC)
you are still reading all the file input fully into memory, what would not work for REALLY LARGE files. You may initialize the buffer to an arbitrary length (a few MB?) and process the input file as chunked

Decrypting of AES/CBC/PKCS5Padding Error: Given final block not properly padded

I'm getting Given final block not properly padded error while decrypting AES/CBC/PKCS5Padding cipher on large encrypted file.
I think this issue is caused by adding wrong initialization vector in cipher.init() method.
I can't read whole file at runtime, so i need to encrypt fixed-size blocks. At this point I'm creating IV and storing it to .txt file. But in decrypting method I'm using the same IV every decryption cycle. How should I change this?
Encryption:
void encrypt() throws Exception{
char[] password = passwordText.getText().toCharArray();
byte[] salt = new byte[8];
/* Creating and saving salt */
salt = saveSalt(salt);
/* Securing password */
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
KeySpec spec = new PBEKeySpec(password, salt, 65536, 128);
SecretKey tmp = factory.generateSecret(spec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
if (choosedFile != null) {
/* Choosing algorithm for decryption */
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
/* Getting plain file */
CipherInputStream fis = new CipherInputStream(new FileInputStream(choosedFile), cipher);
CipherOutputStream fos = new CipherOutputStream(new FileOutputStream(choosedFile+".encrypted"), cipher);
/* Encrypting and Measuring */
long startTime = System.currentTimeMillis();
cipher.init(Cipher.ENCRYPT_MODE, secret);
byte[] rawText = new byte[128];
int count;
while((count = fis.read(rawText)) > 0) {
System.out.println(count);
byte[] encryptedText = cipher.doFinal(rawText);
fos.write(encryptedText, 0, count);
}
long stopTime = System.currentTimeMillis();
fis.close();
fos.close();
/* Creating initialization vector and storing*/
byte[] iVector = cipher.getIV();
saveIVector(iVector);
text.setText(text.getText() + "File was encrypted in " + (stopTime - startTime) + "ms.\n");
}
}
Decryption:
void decrypt() throws Exception {
/* Getting salt */
byte[] salt = getSalt();
/* Getting initialization vector */
byte[] iVector = getIVector();
/* Getting user password */
char[] password = passwordText.getText().toCharArray();
/* Securing password */
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
KeySpec spec = new PBEKeySpec(password, salt, 65536, 128);
SecretKey tmp = factory.generateSecret(spec);
SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "AES");
if (choosedFile != null) {
/* Choosing algorithm for decryption */
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
/* Getting ciphered file */
CipherInputStream fis = new CipherInputStream(new FileInputStream(choosedFile), cipher);
CipherOutputStream fos = new CipherOutputStream(new FileOutputStream(choosedFile+".decrypted"), cipher);
/* Decrypting and Measuring */
long startTime = System.currentTimeMillis();
cipher.init(Cipher.DECRYPT_MODE, secret, new IvParameterSpec(iVector));
byte[] rawText = new byte[128];
int count;
while((count = fis.read(rawText)) > 0) {
byte[] encryptedText = cipher.doFinal(rawText);
fos.write(encryptedText, 0, count);
}
long stopTime = System.currentTimeMillis();
fis.close();
fos.close();

When using CipherInputStream and CipherOutputStream, the streams handle all the calls to the cipher (that's why you pass the cipher to it on initialization). You just need to initialize it correctly, and stream the data through the stream, and the cipher stream will do the needed calls to update() and doFinal(). Remember to close the steams to trigger the doFinal().
Currently your code passes the data through the cipher several times in an uncontrolled way, and the data is messed up.
Also, you only need a CipherInputStream for decrypt, and a CipherOutputStream for encrypt. In your current code you use both for both encrypt and decrypt.
Encrypt could be something like this (this don't handle the iv ..):
...
cipher.init(Cipher.ENCRYPT_MODE, secret);
InputStream is = new FileInputStream(choosedFile);
OutputStream os = new CipherOutputStream(new FileOutputStream(choosedFile+".encrypted"), cipher);
byte[] buffer = new byte[1024];
int len;
while ((len = is.read(buffer)) != -1) {
os.write(buffer, 0, len);
}
is.close();
os.close();
...

Worried about "until I had to cut large file into fixed-size blocks".
Using "chunk" in place of "block" above because "block"has a specific meaning in block ciphers such as AES.
What are toy doing with the chunks, concatenating them?
With CBC mode, after the first block the the previous encrypted block value is effectively used as the IV for the next block. So when splitting and then concatenating the chunks the value of the last block of the previous chunk is the IV for the next chunk.
See CBC mode.
Or are you doing something completely different?

RSA encryption in Android

I am writing a program which employs RSA in Android. I have the following problem:
I am getting the RSA keys:
KeyPair kp = kpg.genKeyPair();
publicKey = kp.getPublic();
privateKey = kp.getPrivate();
Using the encryption function to encrypt a test string:
String test ="test";
byte[] testbytes = test.getBytes();
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] cipherData = cipher.doFinal(testbytes);
String s = new String(cipherData);
Log.d("testbytes after encryption",s);
In the decryption function i am decrypting the data back to get the original string
Cipher cipher2 = Cipher.getInstance("RSA");
cipher2.init(Cipher.DECRYPT_MODE, privateKey);
byte[] plainData = cipher.doFinal(cipherData);
String p = new String(plainData);
Log.d("decrypted data is:",p);
The data in 'p' printed out in the log does not match the original string "test" . Where am I going wrong in this?

Here an example on how to do it, BUT in practice,
You can't really encrypt and decrypt whole files with just RSA. The
RSA algorithm can only encrypt a single block, and it is rather slow
for doing a whole file.
You can encrypt the file using
3DES or AES, and then encrypt the AES key using intended recipient's
RSA public key.
Some code:
public static void main(String[] args) throws Exception {
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
kpg.initialize(1024);
KeyPair keyPair = kpg.generateKeyPair();
PrivateKey privKey = keyPair.getPrivate();
PublicKey pubKey = keyPair.getPublic();
// Encrypt
cipher.init(Cipher.ENCRYPT_MODE, pubKey);
String test = "My test string";
String ciphertextFile = "ciphertextRSA.txt";
InputStream fis = new ByteArrayInputStream(test.getBytes("UTF-8"));
FileOutputStream fos = new FileOutputStream(ciphertextFile);
CipherOutputStream cos = new CipherOutputStream(fos, cipher);
byte[] block = new byte[32];
int i;
while ((i = fis.read(block)) != -1) {
cos.write(block, 0, i);
}
cos.close();
// Decrypt
String cleartextAgainFile = "cleartextAgainRSA.txt";
cipher.init(Cipher.DECRYPT_MODE, privKey);
fis = new FileInputStream(ciphertextFile);
CipherInputStream cis = new CipherInputStream(fis, cipher);
fos = new FileOutputStream(cleartextAgainFile);
while ((i = cis.read(block)) != -1) {
fos.write(block, 0, i);
}
fos.close();
}