Files are truncated while decrypting

Question

I have written the following code to encrypt and decrypt files using the java crypto libraries.

import java.io.*;
import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;

class Blowfish {
    public static void main(String[] args) throws Exception {
        String s;
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        Cipher encrypt = Cipher.getInstance("DES");
        Cipher decrypt = Cipher.getInstance("DES");
        System.out.print("Enter the key: ");
        s = br.readLine();
        /*
         * Names of algorithms used "Blowfish" "DES" 64 bit key ie. 8 bytes
         * "AES" key size has to be 16 bytes ie. 128 bits
         */

        byte key[] = new byte[8];
        for (int i = 0; i < s.length() && i < 8; i++)
            key[i] = (byte) s.charAt(i);

        encrypt.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "DES"));
        FileInputStream fin = new FileInputStream("test.txt");
        FileOutputStream out = new FileOutputStream("encrypted.p4e");
        CipherOutputStream cout = new CipherOutputStream(out, encrypt);

        int input = 0;
        while ((input = fin.read()) != -1) {
            cout.write(input);
        }

        out.close();
        cout.close();
        System.out.println("Starting the decryption");
        System.out.print("Enter the key: ");
        s = br.readLine();

        byte key2[] = new byte[8];
        for (int i = 0; i < s.length() && i < 8; i++)
            key2[i] = (byte) s.charAt(i);

        decrypt.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key2, "DES"));
        fin = new FileInputStream("encrypted.p4e");
        out = new FileOutputStream("test2.txt");
        CipherInputStream in = new CipherInputStream(fin, decrypt);
        input = 0;
        while ((input = in.read()) != -1) {
            out.write(input);
        }
        out.close();
        in.close();
    }
}

However when I tried testing it on a sample .txt file, encryption and decryption ran error free. However the decrypted file wasn't exactly same as the original one... some of the ending part was truncated.

the test file

test file for encryption.. checking the correctness

encrypting using -> pralhad

after decryption using the key -> pralhad

test file for encryption.. checking the

Please suggest some solution.

score 1 · Answer 1 · answered Apr 03 '11 at 22:47

1

You need to remove the out.close() on the first FileOutputStream for encrypted.p4e. That stream is wrapped by CipherOutputStream and the cout.close() will handle closing the underlying stream. By closing that underlying stream early you lose what CipherOutputStream has buffered for the current cipher block.

FileInputStream fin = new FileInputStream("test.txt");
FileOutputStream out = new FileOutputStream("encrypted.p4e");
CipherOutputStream cout = new CipherOutputStream(out, encrypt);
int input = 0;
while ((input = fin.read()) != -1) {
    cout.write(input);
}
out.close(); // remove this line and it works
cout.close();

answered Apr 03 '11 at 22:47

WhiteFang34

70,765
18
106
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Pralhad, this seems to be the correct answer. If you are still around, please accept it. – Maarten Bodewes Oct 14 '12 at 22:39
In addition to closing the stream CipherOutputStream finalizes the encryption which is crucial for block ciphers such as AES in a non streaming mode such as CBC – peerless-phreap May 06 '22 at 00:58

score 1 · Answer 2 · answered Sep 03 '11 at 04:59

1

key[i]=(byte)s.charAt(i);

Due to this fact that character size of Java is 2 bytes, I think there is a problem in casting char to byte. half of the Information will be truncated. harsh if you use other characters than first 128 chars.

answered Sep 03 '11 at 04:59

Ehsan K. Mohammadi

125
1
8

score 0 · Answer 3 · answered Apr 03 '11 at 18:28

0

Try before you close cout call flush():

cout.flush()

answered Apr 03 '11 at 18:28

lukastymo

26,145
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The `close()` does a flush (see [this thread](http://stackoverflow.com/questions/2732260/in-java-when-i-call-outputstream-close-i-always-need-to-call-outputstream-flus)). The problem here is something else. – WhiteFang34 Apr 03 '11 at 22:55

Files are truncated while decrypting

3 Answers3