Re: [OT] Is calculating an MD5 hash of a Rjindael encrypted block and it's key insecure?

[Marcel Weber <mmweber@ncpro.com>]

Richard Atterer wrote:

> On Thu, Aug 12, 2004 at 01:56:53PM +0200, Marcel Weber wrote:
>
>
>
> No, it doesn't mean that. Current browsers will cache the password, AFAIK
> until the end of the session by default, and forever if you enable the
> option "Remember this password" or similar.

I know.

> > - No more credentials that are sent in plain over the internal network 
> > (which is the case if you use basic authentication), except for the 
> > initial login.
>
>
> Hmm, but the initial time is enough... :-/ You will need to use SSL for 
> that.

It's already used ;-)
> > The block size of the data to be encrypted has to come in chunks of 16
> > bytes. I always append random numbers to the credentials, ip and time
> > strings to the next 16 bytes before encryption. Like this, the attacker
> > cannot know or guess all of the content of the encrypted data, can he?
>
>
> This makes things more difficult for the attacker, yes. Presumably your
> code adds no random padding if the data already has the right length, but
> still...

Well it adds random values even if the block size would fit.

> > The trouble is, as far I figured out, that Crypt::Rjindael does not
> > return, when you try to decrypt an encrypted string that's, a. damaged or
> > b. encrypted with a different key. Don't know why.
>
>
> This cannot be. Rijndael gets bits as input, and it outputs bits. The only
> thing that will happen is that you'll get random-looking garbage if the
> input is incorrect in some way. (I don't know what Crypt::Rjindael does.)

Well I figured this out. It was a non ending loop in my code, as I 
looked for a special character in the decrypted key. Very dumb of me...

> > > Why $s? Surely you'll only store $c in the cookie, otherwise there's no
> > > point in encrypting the data.
> >
> > Ahem, well $s is encrypted and $c is only a md5 checksum for $s and $k. 
>
>
> Sorry, I misinterpreted your message and thought that $s was not encrypted.
>
> Cheers,
>
>   Richard

Thanks again

Marcel