Getting first 8 or 16 bytes scrambled after decryption + write procedures

Question

Problem description:
Properly initiated Cipher object is performing encryption operation over 1Kb packets of bytes which originate from user defined file: file is encrypted and then written on user chosen drive. Then, after �some� time, user loads encrypted file and decrypts it with same initialization values for Cipher operating in decipher mode: decrypted materiel is written on drive (under new file name � if desired).
When opened, decrypted file is OK except first 8 bytes (16 bytes in case of AES). Ciphers used are provided by JCE, and they are following: DES, DESede, Blowfish, AES and PBEwithMD5andDES.
My guess is that problem lies in write operations in RandomAccessFile class (encoding?), or in Cipher operations over the first byte (encoding?)�
Here is a part of code that does the encryption/decryption (depending on initiation):
(in run() method of a Thread object�)
Int offset=0;
try {
//positioning cursor at the beginning of a file
GlavniObrazac.fajl.seek(0);
GlavniObrazac.tempFajl.seek(0);
/*operations over 1KB blocks (cikl � number of whole blocks in file, reminder will be handled afterwards). GlavniObrazac � main frame of windowed application � ignore this
for (int x = 1; x <= GlavniObrazac.cikl; x++) {
GlavniObrazac.fajl.readFully(bafer, 0, 1024);
GlavniObrazac.fajl.seek(ofset + 1024);
bafer2 = c.update(bafer);
//ucitavanje kriptovanog materijala u osnovni bafer ->
GlavniObrazac.tempFajl.write(bafer2, 0, bafer2.length);
GlavniObrazac.tempFajl.seek(ofset + bafer2.length);
//pomeranje kursora za narednih 1024
ofset += bafer2.length;
//handling reminder of a file, reminder is always < 1KB
// pozicijaOstatka � length of reminder
GlavniObrazac.fajl.readFully(bafer, 0, GlavniObrazac.pozicijaOstatka);
bafer2 = c.doFinal(bafer);
//upisivanje preostalih podataka u temporary fajl na disku
GlavniObrazac.tempFajl.write(bafer2, 0, bafer2.length); //GlavniObrazac.pozicijaOstatka
} catch (Exception e) {
GlavniObrazac.jTextArea1.append(�Error :�+e);
NOTE: fajl and tempFajl are RandomAccessFile objects. close() operation is performed when user decides to save file / or exit.
Sorry for formatting, this is imported from MS Word.

Answer 1

Answers:
1)Good hint - but does not answer the question. I
will use proposed method for experiments in another
implementation. Application that uses encryption does
other things besides encryption: basicly it loads
files and does something with them. That is the
reason for use of RandomAccessFile.Are you trying to jump into the middle of the file and decrypt just a single 1K buffer? If so then you need to initialise the CFB mode with the IV as it was at that same point in the encryption. This will not be the IV that the cipher was initialised with.
2)Cipher is initiated properly, but that peace of
code is not visible from what I have had sent to
formum. I thought that problem is trivial, and that
no details are needed because I expected that someone
will quickly reckognise something that he/she have
already seen before.I have seen similar before but with CBC mode not CFB. Looking at your code I don't think the cipher is initialised properly. In encryption mode you do not provide an IV yet you do in decryption mode!
3)All initialisation data for the cipher (like key,
salt etc.) are exactly the same in both operations
(encryption/decryption). Results are OK, except first
8 bytes (16 in case of AES).Which is exactly the symptoms you get if the decryption IV is wrong!
>
Whole application has 24 user created classes (so
far), so it would be difficult to post all materiel
that is connected to encryption.Obviously designed for testablility!
>
However, here is a piece from initiating loop (switch
method) that initiates Blowfish, after which run()
method i posted yesterday takes over and does the
encryption or decryption.
/* .... switch(whichOneToUse)....*/
case 2: // Blowfish
imeAlgor = "Blowfish";//just name of algho
c =
Cipher.getInstance("Blowfish/CFB/NoPadding",
"SunJCE");
if (GlavniObrazac.nova) {//if encryption
c.init(Cipher.ENCRYPT_MODE, K);WHY NO IV WHEN THE DECRYPTION MODE HAS AN IV? At least I assume that the parameter 'ap' is an IV!
mode = " ENCRYPT_MODE";
} else {//else decryption
c.init(Cipher.DECRYPT_MODE, K,
ap);//ap-algoParams, exist as static var
mode = " DECRYPT_MODE";