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I'm working with Java's encryption library and getting a IllegalBlockSizeException.

I am currently trying to extract database contents in XML file format. During the data dump, I am creating a manifest file with a string that gets decrypted using a key defined in the database.

Later, when the contents of the XML's files are loaded into another database, it gets the key from that database and uses it to decrypt the manifest. If the decrypted manifest does not match the original contents, that means the encryption keys in the source and destination databases do not match and the user is notified of this.

The following is the code. The EncryptionEngine object is a singleton that uses the Java encryption library to abstract away a lot of the details of encryption. Assume that it works correctly, as it's fairly old and mature code.

This is all in a class I've made. First, we have these data members:

private final String encryptedManifestContents;
private final static String DECRYPTED_MANIFEST_CONTENTS = "This file contains the encrypted string for validating data in the dump and load process";
final static String ENCRYPTED_MANIFEST_FILENAME = "manifest.bin";

First the encryption process. The string is encrypted like the following:

final EncryptionEngine encryptionEngine = EncryptionEngine.getInstance();
encryptedManifestContents = encryptionEngine.symmetricEncrypt(DECRYPTED_MANIFEST_CONTENTS); // The contents get converted to bytes via getBytes("UTF-8")

Then written to the manifest file (destination is just a variable holding the file path as a string):

EncryptedManifestUtil encryptedManifestUtil = new EncryptedManifestUtil(); // The class I've created.  The constructor is the code above, which just initialized the EncryptionEngine and encrypted the manifest string.
manifestOut = new FileOutputStream(destination + "/" + ENCRYPTED_MANIFEST_FILENAME);
manifestOut.write(encryptedManifestUtil.encryptedManifestContents.getBytes("UTF-8"));

At this point, the encryption process is done. We've taken a String, encrypted it, and written the contents to a file, in that order. Now when someone loads the data, the decryption process starts:

BufferedReader fileReader = new BufferedReader(new FileReader(filename)); // Filename is the manifest's file name and location
final EncryptionEngine encryptionEngine = EncryptionEngine.getInstance();
String decryptedManifest = encryptionEngine.decryptString(fileReader.readLine().getBytes("UTF-8")); // This is a symmetric decrypt

When the decryption happens, it throws this exception:

Caused by: javax.crypto.IllegalBlockSizeException: last block incomplete in decryption
    at org.bouncycastle.jcajce.provider.symmetric.util.BaseBlockCipher.engineDoFinal(Unknown Source)
    at javax.crypto.Cipher.doFinal(DashoA13*..)

It appears to read and write correctly to the file, but the contents are gibberish to me. The result from the fileReader.readLine() is: 

9�Y�������䖷�߾��=Ă���    s7Cx�t�b��_-(�b��LFA���}�6�f����Ps�n�����ʢ�@��  �%��%�5P�p

Thanks for the help.

EDIT: So I changed the way I write to a file.

Recall this line:

encryptedManifestContents = encryptionEngine.symmetricEncrypt(DECRYPTED_MANIFEST_CONTENTS);

The encrypt first gets the bytes from the inputted string, then decrypts, then changes the bytes back to a string by first encoding it to the base 64 bytes. Then it converts the base 64 bytes array back to a string.

With this in mind, I changed the file writer to a PrintWriter instead of a FileOutputStream and directly write the string to the file instead of the bytes. I'm still getting the error unfortunately. However there seem to be less of the � in the resulting String from the read line.

user207421
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Slims
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  • Why do `getBytes()` on the encrypted string before writing? – Lee Meador Apr 08 '13 at 18:54
  • You've shown us everything except the relevant code: the one which actually encrypts and decrypts. – JB Nizet Apr 08 '13 at 18:58
  • I am hoping the problem lies in how I am reading/writing to a file. I cannot directly show you the code for the encryption since it belongs to my company. If necessary, I can do a rough outline of it. – Slims Apr 08 '13 at 19:08
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    Your description of the encryption process doesn't make much sense. Believe me, there is no secret than anyone would be interested in inside your encryption. If you want help, post your code, or hire a consultant and make him sign an NDA. Voting to close as too localized. – JB Nizet Apr 08 '13 at 19:19
  • It's kind of a hacky way of verifying the DB's encryption key, which is probably why it doesn't appear to make much sense. Also, I realize no one cares about the secrets inside the EncryptionEngine, but I am just a lowly software engineer in my company and I am not at liberty to show the source code :( – Slims Apr 08 '13 at 19:23
  • The answer was indeed the way I was using the IO streams as I suspected. No need to close. – Slims Apr 08 '13 at 19:29

2 Answers2

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It looks like the problem is with your fileReader.readLine() - you're writing a byte stream to a file, and then reading it back in as a string. Instead, you should either read in a byte stream, e.g. refer to this question, or else use Base64 Encoding to convert your byte array to a string, write it to a file, read it from a file, and convert it back to a byte array.

Community
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Zim-Zam O'Pootertoot
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  • Try decrypting the encrypted byte array without writing it to or reading it from a file, in order to determine if the problem is with your encryption/decryption or if the problem is with your IO. – Zim-Zam O'Pootertoot Apr 08 '13 at 19:17
  • This worked, actually. I forgot to reload the data so I was using the old manifest written the wrong way :) – Slims Apr 08 '13 at 19:29
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I believe you are incorrectly using a Reader which is an object defined to read characters when you actually want to be dealing strictly in bytes. This is most likely not the entirety of your problem but if you are writing bytes you should read bytes not characters.

Deadron
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