RE: AES-256 encryption

[Mike Messick <mikem () tridigitalenterprises com>]

Hi Dereck,

I'm assuming your referring to loop-aes, (http://loop-aes.sourceforge.net)
as opposed to the cryptoloop feature in newer linux kernels.  If not, then
please disregard my comments as I'm only familiar with loop-aes.

I'm also not a crypto mathematician, so I can't comment on *exactly* how
long a brute-force attack would take and will leave this to others more
knowlegeable than me, but brute-force attack against the cyphertext won't
happen in any computationally feasible amount of time (ie we'll all be
long dead before it succeeds.)


If you're using the multi-key-v3 key setup mode, the key itself is
protected against dictionary attacks by GPG and salting (according to the
readme).  But, you're not even talking about attacking the key, rather
your scenario is that the key was not taken along with the hard drive, so
comments about weak passphrases don't apply.

According to http://en.wikipedia.org/wiki/Advanced_Encryption_Standard,
the only successful attacks against the Rijndael algorithm have been side
channel attacks which wouldn't be effective if the key doesn't physically
exist either on the USB or in the system's memory.  (Loop-aes tries to
obfuscate the key in ram by shifting bits around continually to help
prevent this type of attack, but it might still be possible if the key is
in ram when it's stolen?)

The algorithm itself has been declared sufficient for protecting US
Top-Secret information when a 192-bit or 256-bit key has been used to
encrypt the data provided the NSA has approved the implementation of the
algorithm.

Short answer - it's probably the most secure open-source algorithm we can
get our hands on for the foreseeable future and will protect your system
from being accessed by street-level criminals and even corporate infosec
thugs.  National level intelligence - well, if the NSA is after you,
you'll have far worse problems than your machine being stolen. 

I'm sure someone else will post something more intelligent than this but I
hope it helps.

==================================================================
Mike Messick           Dona nobis pacem          rm -rf /bin/laden
PGP Key Fingerprint:                       email: mikem () alaska net 
2048/0x57318496 053B 412B 82FC 3808 E141  CDCD 74AE 01C5 5731 8496

On Tue, 21 Aug 2007, 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 () securityfocus com [mailto:listbounce () securityfocus com] On Behalf Of Michel Pereira
> Sent: Tuesday, August 21, 2007 2:01 PM
> To: adrian.floarea
> Cc: 'R Buena'; 'Kush Wadhwa'; pen-test () securityfocus com; forensics () securityfocus com
> 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 ªerban Vodã St., Building C1, 2nd floor
> > 040205 Bucharest 4, Romania
> >
> > -----Original Message-----
> > From: R Buena [mailto:dreamsbig () gmail com]
> > Sent: Thursday, August 16, 2007 6:09 PM
> > To: adrian.floarea
> > Cc: Kush Wadhwa; pen-test () securityfocus com; forensics () securityfocus com
> > 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 () uti ro> 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 ªerban Vodã St., Building C1, 2nd floor
> > > 040205 Bucharest 4, Romania
> > >
> > > -----Original Message-----
> > > From: listbounce () securityfocus com [mailto:listbounce () securityfocus com
> > > ] On
> > > Behalf Of Kush Wadhwa
> > > Sent: Tuesday, August 14, 2007 1:36 PM
> > > To: pen-test () securityfocus com; forensics () securityfocus com
> > > 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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Need to secure your web apps NOW?
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Click to try it, buy it or download a solution FREE today!

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