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Encryption problem with CipherInputStream/CipherOutputStream

 
 
joven.chiew@gmail.com
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      07-16-2012
Hi I have the following code I tested to encrypt/decrypt file and all is good. It works correctly for full file encryption and now I want to test partial encryption of 100000 bytes. I tried read the 100000 from a text file full of "qwerty" text and encrypt it in another file and I am able to decryptthis file back to the 100000 bytes of "qwerty" output to a new test file.

So it seems like the partial encryption is ok, all I need is implement CipherInputStream to decrypt the first 100000 bytes write to a output file and do a normal FileInputStream and write to the output write. Theoretically I should have implemented the partial file encryption/decryption.

Now, when I open the output file, I saw unreadable character at EOL. What is wrong, how can I correct it?

EOF -> "qwertyqwertyqwertyqwertyqwertyqwertyw']uX\aQ2IܱTN'"

Cheers.

public static void encryptFile(SecretKey key, File sourceFile,
File secretFile) throws Exception {
byte[] salt = new byte[8];
Random random = new Random();
random.nextBytes(salt);

final int BUFF_SIZE = 100000;
final byte[] buffer = new byte[BUFF_SIZE];

PBEParameterSpec spec = new PBEParameterSpec(salt, ITERATIONCOUNT);
Cipher cipher = Cipher.getInstance(ALGORITHM2);
cipher.init(Cipher.ENCRYPT_MODE, key, spec);

InputStream in = null;
OutputStream out = null;
in = new FileInputStream(sourceFile);
out = new FileOutputStream(secretFile);
CipherOutputStream cos = new CipherOutputStream(out, cipher);

try {
out.write(salt);
boolean pEncrypt = true;
while (true) {
synchronized (buffer) {
int amountRead = in.read(buffer);
if (amountRead == -1) {
break;
}
if (pEncrypt) {
cos.write(buffer, 0, amountRead);
pEncrypt = false;
} else {
out.write(buffer, 0, amountRead);
}
}
}
} finally {
if (in != null) {
in.close();
}
if (cos != null) {
cos.close();
out.close();
}
}
}

public static void decryptFile(SecretKey key, File secretFile,
File decryptFile) throws Exception {
byte[] salt = new byte[8];

final int BUFF_SIZE = 100000;
final byte[] buffer = new byte[BUFF_SIZE];

InputStream bis = null;
OutputStream out = null;
bis = new FileInputStream(secretFile);
out = new FileOutputStream(decryptFile);

bis.read(salt);

PBEParameterSpec spec = new PBEParameterSpec(salt, ITERATIONCOUNT);
Cipher cipher = Cipher.getInstance(ALGORITHM2);
cipher.init(Cipher.DECRYPT_MODE, key, spec);

CipherInputStream in = new CipherInputStream(bis, cipher);

int b = 1;
Boolean pEncrypt = true;
while (true) {
synchronized (buffer) {
if (pEncrypt) {
b = in.read(buffer);
pEncrypt = false;
} else {
b = bis.read(buffer);
}
if (b == -1) {
break;
}
out.write(buffer, 0, b);
}
}
out.close();
bis.close();
in.close();
}
 
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Daniel Pitts
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Posts: n/a
 
      07-16-2012
On 7/15/12 11:59 PM, http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:
> Hi I have the following code I tested to encrypt/decrypt file and all is good. It works correctly for full file encryption and now I want to test partial encryption of 100000 bytes. I tried read the 100000 from a text file full of "qwerty" text and encrypt it in another file and I am able to decrypt this file back to the 100000 bytes of "qwerty" output to a new test file.
>
> So it seems like the partial encryption is ok, all I need is implement CipherInputStream to decrypt the first 100000 bytes write to a output file and do a normal FileInputStream and write to the output write. Theoretically I should have implemented the partial file encryption/decryption.
>
> Now, when I open the output file, I saw unreadable character at EOL. What is wrong, how can I correct it?


Please don't use tabs in usenet.

I've snipped your source from this reply, but what was striking to me
was that you used the COS for only the first write, and then never
flushed it. COS may have some buffering behind the scenes. Even if you
call flush on it, that may not be sufficient as many block ciphers
require a full block before they can produce output. You seem to want
to mix encrypted and unencrypted data in the same output stream, which
seems dubious at best, since you don't have any clear demarcation of
where the various data start and end.
 
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