I'm trying to encrypt and decrypt a file using a key that the user typed. All
these operations are done in Android. At the moment I decrypt I get a
javax.crypto.BadPaddingException: pad block corrupted. The same code works
normally on Windows PC. Why?
Here is my code:
*The call:*
*Encrypt:*
String fileNameInput =
Environment.getExternalStorageDirectory().toString() + File.separator +
SAVE_FOLDER + File.separator + "file";
String fileNameOutput =
Environment.getExternalStorageDirectory().toString() + File.separator +
AVE_FOLDER + File.separator + "file_crypted";
Crypto c = new Crypto(userKey);
c.encrypt(new FileInputStream(fileNameInput), new
FileOutputStream(fileNameOutput));
*Decrypt:*
String fileNameInput =
Environment.getExternalStorageDirectory().toString() + File.separator +
SAVE_FOLDER + File.separator + "file_crypted";
String fileNameOutput =
Environment.getExternalStorageDirectory().toString() + File.separator +
AVE_FOLDER + File.separator + "file_decrypted";
Crypto c = new Crypto(userKey);
c.encrypt(new FileInputStream(fileNameInput), new
FileOutputStream(fileNameOutput));
*The class Crypto:*
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.security.spec.AlgorithmParameterSpec;
import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import android.graphics.Bitmap;
import br.com.italomr.photocrypt.util.Domain;
import br.com.italomr.photocrypt.util.StringOutputStream;
public class Crypto {
private Cipher ecipher;
private Cipher dcipher;
private static final String AES = "AES";
private static final String AES_PADDING = "AES/CBC/PKCS5Padding";
private static final String MD5 = "MD5";
private static final String HEXES = "0123456789ABCDEF";
/**
* Input a string that will be md5 hashed to create the key.
*
* @return void, cipher initialized
*/
public Crypto() {
try {
KeyGenerator kgen = KeyGenerator.getInstance(AES);
kgen.init(128);
this.setupCrypto(kgen.generateKey());
} catch (Exception e) {
e.printStackTrace();
}
}
public Crypto(String key) {
SecretKeySpec skey = new SecretKeySpec(getMD5(key), AES);
this.setupCrypto(skey);
}
private void setupCrypto(SecretKey key) {
// Create an 8-byte initialization vector
byte[] iv = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f };
AlgorithmParameterSpec paramSpec = new IvParameterSpec(iv);
try {
ecipher = Cipher.getInstance(AES_PADDING);
dcipher = Cipher.getInstance(AES_PADDING);
// CBC requires an initialization vector
ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
} catch (Exception e) {
e.printStackTrace();
}
}
// Buffer used to transport the bytes from one stream to another
byte[] buf = new byte[1024];
public void encrypt(InputStream in, OutputStream out) {
try {
// Bytes written to out will be encrypted
out = new CipherOutputStream(out, ecipher);
// Read in the cleartext bytes and write to out to encrypt
int numRead = 0;
while ((numRead = in.read(buf)) >= 0) {
out.write(buf, 0, numRead);
}
out.close();
} catch (java.io.IOException e) {
e.printStackTrace();
}
}
public byte[] encrypt(byte[] data) {
try {
byte[] ciphertext = ecipher.doFinal(data);
return ciphertext;
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
public void decrypt(InputStream in, OutputStream out) {
try {
// Bytes read from in will be decrypted
in = new CipherInputStream(in, dcipher);
// Read in the decrypted bytes and write the cleartext to out
int numRead = 0;
while ((numRead = in.read(buf)) >= 0) {
out.write(buf, 0, numRead);
}
out.close();
} catch (java.io.IOException e) {
e.printStackTrace();
}
}
public byte[] decrypt(byte[] ciphertext) {
try {
// To convert to String
// String plaintext = new String(dcipher.doFinal(ciphertext),
// Domain.UTF8);
return dcipher.doFinal(ciphertext);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
private static byte[] getMD5(String input) {
try {
byte[] bytesOfMessage = input.getBytes(Domain.UTF8);
MessageDigest md = MessageDigest.getInstance(MD5);
return md.digest(bytesOfMessage);
} catch (Exception e) {
return null;
}
}
public static String byteToHex(byte[] raw) {
if (raw == null) {
return null;
}
final StringBuilder hex = new StringBuilder(2 * raw.length);
for (final byte b : raw) {
hex.append(HEXES.charAt((b & 0xF0) >>
4)).append(HEXES.charAt((b & 0x0F)));
}
return hex.toString();
}
public static byte[] hexToByte(String hexString) {
int len = hexString.length();
byte[] ba = new byte[len / 2];
for (int i = 0; i < len; i += 2) {
ba[i / 2] = (byte) ((Character.digit(hexString.charAt(i), 16)
<< 4) + Character.digit(hexString.charAt(i + 1), 16));
}
return ba;
}
}
Thanks in advance.
Ítalo Rocha
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