Re: AES-256 encryption



Hi Dereck and list,

The cipher itself is not easily cracked (and by cracked I mean
decryptable without the key with a reasonable amount of CPU cycles,
given a reasonably strong key), but the implementation can be weak. One
such weakness is the so-called watermark attack. See

http://www.governmentsecurity.org/archive/t14922.html

There is proof of concept code there --- it is easy enough that I give
it to my students as an assignment.

For more information, see also

http://mareichelt.de/pub/texts.cryptoloop.php (I don't agree with
everything written there, but its worth the read.)


As an aside (since this thread has drifted --- surprise), it would be
nice to have a compendium of references comparing encryption techniques,
their strengths and weaknesses. Something practical, what works and
what doesn't. The journals concentrate on the ciphers/hashes and their
strengths (eg. the recent sha1 weakness discovered by Wang et al.) but
I think the biggest problem is poor implementation (eg. problems with
how the initialization vector is handled, etc.)


Anthony Basile, Chair IT
D'Youville College
Buffalo, NY USA


Dereck Martin wrote:
I use an encrypted file system in Linux using a loopback device with AES-256 encryption and the password is a symmetric GPG key on a USB device required a boot (which also contains the boot partition). What would be the likely hood of breaking the encryption if the disk was taken, but the GPG key required to unlock it was not.

Dereck Martin
Network Operations Engineer
PacketDrivers IT Outsourcing, LLC
http://www.packetdrivers.com
____ _ _ ____ _
| _ \ __ _ ___| | _____| |_| _ \ _ __(_)_ _____ _ __ ___
| |_) / _` |/ __| |/ / _ \ __| | | | '__| \ \ / / _ \ '__/ __|
| __/ (_| | (__| < __/ |_| |_| | | | |\ V / __/ | \__ \
|_| \__,_|\___|_|\_\___|\__|____/|_| |_| \_/ \___|_| |___/


-----Original Message-----
From: listbounce@xxxxxxxxxxxxxxxxx [mailto:listbounce@xxxxxxxxxxxxxxxxx] On Behalf Of Michel Pereira
Sent: Tuesday, August 21, 2007 2:01 PM
To: adrian.floarea
Cc: 'R Buena'; 'Kush Wadhwa'; pen-test@xxxxxxxxxxxxxxxxx; forensics@xxxxxxxxxxxxxxxxx
Subject: Re: AES-256 encryption

But this tools can tell you if the correct key was found? Or you need
to see every output that the tool does.

Bye

On 16/08/2007, at 12:49, adrian.floarea wrote:


As I say to Kush in a private email, it is almost impossible to
crack a file which is encrypted in a proper way with AES.

But, if the password used for encryption is a week password (like
1234 or abcd etc) with a specialized tool you can break the
encryption.

Even, if the password is weak some tools cannot decrypt the files,
because do not understand the format of the document (for example,
if the document is a PKCS#7 structure), so in this case you must use
an appropriate tool.

This was the sense of my words.

Hope to help you.

Regards,


Adrian Floarea, CISA
Business Development Manager
SC CERTSIGN srl
Central Business Park
133, Calea Şerban Vodă St., Building C1, 2nd floor
040205 Bucharest 4, Romania

-----Original Message-----
From: R Buena [mailto:dreamsbig@xxxxxxxxx]
Sent: Thursday, August 16, 2007 6:09 PM
To: adrian.floarea
Cc: Kush Wadhwa; pen-test@xxxxxxxxxxxxxxxxx; forensics@xxxxxxxxxxxxxxxxx
Subject: Re: AES-256 encryption

Just curious, what if the program was KeyPass or PasswordSafe?
and you don't know the passphrase?

On 8/14/07, adrian.floarea <adrian.floarea@xxxxxx> wrote:

Hi Kush,

Please tell me if you know the program which was used for encrypt
the file
and also the used password. If not, I am afraid that will be
impossible for
you to decrypt the file.

There are some good programs for decrypt files (for example
Passware) but
with limited functionalities. For example if was used for
encryption a good
password (more than 6-7 characters, numbers or special characters)
it is
almost impossible to recover the file.

Regards,

Adrian Floarea, CISA
Business Development Manager
SC CERTSIGN srlr
Central Business Park
133, Calea Şerban Vodă St., Building C1, 2nd floor
040205 Bucharest 4, Romania

-----Original Message-----
From: listbounce@xxxxxxxxxxxxxxxxx [mailto:listbounce@xxxxxxxxxxxxxxxxx
] On
Behalf Of Kush Wadhwa
Sent: Tuesday, August 14, 2007 1:36 PM
To: pen-test@xxxxxxxxxxxxxxxxx; forensics@xxxxxxxxxxxxxxxxx
Subject: AES-256 encryption

Hello All,

Is there any way to decrypt a file which is AES-256 encrypted? I used
many of the tools but I was not able to decrypt it. Please help me if
any one knows how to decrypt it

Regards,
Kush Wadhwa

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--
Só Jesus salva, o homem faz backups
http://www.michel.eti.br




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