Exception - Illegal Block size during decryption(Android)
- by Vamsi
I am writing an application which encrypts and decrypts the user notes based on the user set password. i used the following algorithms for encryption/decryption
1. PBEWithSHA256And256BitAES-CBC-BC
2. PBEWithMD5And128BitAES-CBC-OpenSSL
e_Cipher = Cipher.getInstance(PBEWithSHA256And256BitAES-CBC-BC);
d_Cipher = Cipher.getInstance(PBEWithSHA256And256BitAES-CBC-BC);
e_Cipher.init()
d_Cipher.init()
encryption is working well, but when trying to decrypt it gives
Exception - Illegal Block size
after encryption i am converting the cipherText to HEX and storing it in a sqlite database. i am retrieving correct values from the sqlite database during decyption but when calling d_Cipher.dofinal() it throws the Exception.
I thought i missed to specify the padding and tried to check what are the other available cipher algorithms but i was unable to found.
so request you to please give the some knowledge on what are the cipher algorithms and padding that are supported by Android? if the algorithm which i used can be used for padding, how should i specify the padding mechanism?
I am pretty new to Encryption so tried a couple of algorithms which are available in BouncyCastle.java but unsuccessful.
As requested here is the code
public class CryptoHelper {
private static final String TAG = "CryptoHelper";
//private static final String PBEWithSHA256And256BitAES = "PBEWithSHA256And256BitAES-CBC-BC";
//private static final String PBEWithSHA256And256BitAES = "PBEWithMD5And128BitAES-CBC-OpenSSL";
private static final String PBEWithSHA256And256BitAES = "PBEWithMD5And128BitAES-CBC-OpenSSLPBEWITHSHA1AND3-KEYTRIPLEDES-CB";
private static final String randomAlgorithm = "SHA1PRNG";
public static final int SALT_LENGTH = 8;
public static final int SALT_GEN_ITER_COUNT = 20;
private final static String HEX = "0123456789ABCDEF";
private Cipher e_Cipher;
private Cipher d_Cipher;
private SecretKey secretKey;
private byte salt[];
public CryptoHelper(String password) throws InvalidKeyException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidAlgorithmParameterException, InvalidKeySpecException {
char[] cPassword = password.toCharArray();
PBEKeySpec pbeKeySpec = new PBEKeySpec(cPassword);
PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt, SALT_GEN_ITER_COUNT);
SecretKeyFactory keyFac = SecretKeyFactory.getInstance(PBEWithSHA256And256BitAES);
secretKey = keyFac.generateSecret(pbeKeySpec);
SecureRandom saltGen = SecureRandom.getInstance(randomAlgorithm);
this.salt = new byte[SALT_LENGTH];
saltGen.nextBytes(this.salt);
e_Cipher = Cipher.getInstance(PBEWithSHA256And256BitAES);
d_Cipher = Cipher.getInstance(PBEWithSHA256And256BitAES);
e_Cipher.init(Cipher.ENCRYPT_MODE, secretKey, pbeParamSpec);
d_Cipher.init(Cipher.DECRYPT_MODE, secretKey, pbeParamSpec);
}
public String encrypt(String cleartext) throws IllegalBlockSizeException, BadPaddingException {
byte[] encrypted = e_Cipher.doFinal(cleartext.getBytes());
return convertByteArrayToHex(encrypted);
}
public String decrypt(String cipherString) throws IllegalBlockSizeException {
byte[] plainText = decrypt(convertStringtobyte(cipherString));
return(new String(plainText));
}
public byte[] decrypt(byte[] ciphertext) throws IllegalBlockSizeException {
byte[] retVal = {(byte)0x00};
try {
retVal = d_Cipher.doFinal(ciphertext);
} catch (BadPaddingException e) {
Log.e(TAG, e.toString());
}
return retVal;
}
public String convertByteArrayToHex(byte[] buf) {
if (buf == null)
return "";
StringBuffer result = new StringBuffer(2*buf.length);
for (int i = 0; i < buf.length; i++) {
appendHex(result, buf[i]);
}
return result.toString();
}
private static void appendHex(StringBuffer sb, byte b) {
sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
}
private static byte[] convertStringtobyte(String hexString) {
int len = hexString.length()/2;
byte[] result = new byte[len];
for (int i = 0; i < len; i++) {
result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
}
return result;
}
public byte[] getSalt() {
return salt;
}
public SecretKey getSecretKey() {
return secretKey;
}
public static SecretKey createSecretKey(char[] password) throws NoSuchAlgorithmException, InvalidKeySpecException {
PBEKeySpec pbeKeySpec = new PBEKeySpec(password);
SecretKeyFactory keyFac = SecretKeyFactory.getInstance(PBEWithSHA256And256BitAES);
return keyFac.generateSecret(pbeKeySpec);
}
}
I will call mCryptoHelper.decrypt(String str) then this results in Illegal block size exception
My Env: Android 1.6 on Eclipse
