Kryptor Whitepaper released

[Angelo-18]

As I announced in previous threads, we released the full white paper of the algorithm implemented in Kryptor (http://www.rosiello.org/archivio/kryptor-0.1.2.tar.gz).

The paper can be found at:
http://www.rosiello.org
or
http://www.rosiello.org/modules/smartsection/item.php?itemid=8

cheers,
Angelo

Rosiello Security,
http://www.rosiello.org

[Omar A. Herrera]

Hi Angelo,

I just took a quick look at it but it seems to me like a polyalphabetic
substitution cipher with an effective block length of 16 bytes (i.e. every
16 bytes you have a monoalphabetic substitution cipher).

I mean, this doesn't hide the underlying language frequencies within each
block of 16 bytes (the length of your MD5 hashed keys). Of course I'm not a
cryptanalyst but it really seems to be crackeable with pen and paper
(granted, probably not as easy as a Vigenère cipher because of the
manipulations of the keys, but not much more difficult though).

Probably the only situations where this cipher is secure is when the length
of the text to be enciphered is <= 16 bytes (the length of your keys),
provided that you do not reuse the keys of course :-).

Pending the opinion of an experienced cryptographer, I would say that even
without the source code the Friedman and Kasisiki tests would quickly show
up the type of the encipherment (polyalphabetic) and the length of the key
(16 bytes).

As far as I know, this is the reason why modern strong symmetric ciphers use
both diffusion and confusion (as suggested by Claude E. Shannon). This piece
of code only implements substitution, and reminds me of a comment made by
Bruce Schneier regarding the simple XOR algorithm (Chapter 1, Foundations)
in his book "Applied Cryptography" ;-):

        ...
        crypted[x] = plainBlock[x] ^ MD5pwd[streamMd5pwd] ;
        ...

Best regards,

Omar A. Herrera

> -----Original Message-----
> From: angelo@... [mailto:angelo@...]
> Sent: Wednesday, February 15, 2006 2:48 PM
> To: focus-linux@...
> Subject: Kryptor Whitepaper released
>
> As I announced in previous threads, we released the full white paper of
> the algorithm implemented in Kryptor
> (http://www.rosiello.org/archivio/kryptor-0.1.2.tar.gz).
>
> The paper can be found at:
> http://www.rosiello.org
> or
> http://www.rosiello.org/modules/smartsection/item.php?itemid=8
>
> cheers,
> Angelo
>
> Rosiello Security,
> http://www.rosiello.org

[Angelo-18]

"I just took a quick look at it but it seems to me like a polyalphabetic
substitution cipher with an effective block length of 16 bytes (i.e. every
16 bytes you have a monoalphabetic substitution cipher). "

Absolutly it's not a polyalphabetic substitution cipher.

"I mean, this doesn't hide the underlying language frequencies within each
block of 16 bytes (the length of your MD5 hashed keys). Of course I'm not a
cryptanalyst but it really seems to be crackeable with pen and paper
(granted, probably not as easy as a Vigenère cipher because of the
manipulations of the keys, but not much more difficult though)."

ARCS is a stream cipher where the keystream is generated thanks an hash function. Since every piece of the keystream depends constantly on the key and on the past of the keystream, every block of the plaintext will get a different underlying sequence of bits (of keystream) to be xored with. It means that you can't assign to a block a crypted string. Every time you will get a different result!
To stay clear...
The string "angelo" could be mapped into every possible string of bits available by the co-domain of the hash function (i.e. 2^128 for MD5, 2^160 SHA-1 etc.)
I hope I was clear and I that could help you.

PS: I invite you to submit any other question into the forum of http://www.rosiello.org

yours,
Angelo

[Omar Herrera]

Ooops,

Didn't read the code well, the keystream is not reused after each iteration,
(Angelo showed me my mistake).

This is what happens when you don't read well and are too quickly to answer
:-). Please disregard my previous comments.

Regards,

Omar

> -----Original Message-----
> From: Omar A. Herrera [mailto:omar.herrera@...]
> Sent: Wednesday, February 15, 2006 8:44 PM
> To: angelo@...; focus-linux@...
> Subject: RE: Kryptor Whitepaper released
>
> Hi Angelo,
>
> I just took a quick look at it but it seems to me like a polyalphabetic
> substitution cipher with an effective block length of 16 bytes (i.e. every
> 16 bytes you have a monoalphabetic substitution cipher).
>
> I mean, this doesn't hide the underlying language frequencies within each
> block of 16 bytes (the length of your MD5 hashed keys). Of course I'm not
> a
> cryptanalyst but it really seems to be crackeable with pen and paper
> (granted, probably not as easy as a Vigenère cipher because of the
> manipulations of the keys, but not much more difficult though).
>
> Probably the only situations where this cipher is secure is when the
> length
> of the text to be enciphered is <= 16 bytes (the length of your keys),
> provided that you do not reuse the keys of course :-).
>
> Pending the opinion of an experienced cryptographer, I would say that even
> without the source code the Friedman and Kasisiki tests would quickly show
> up the type of the encipherment (polyalphabetic) and the length of the key
> (16 bytes).
>
> As far as I know, this is the reason why modern strong symmetric ciphers
> use
> both diffusion and confusion (as suggested by Claude E. Shannon). This
> piece
> of code only implements substitution, and reminds me of a comment made by
> Bruce Schneier regarding the simple XOR algorithm (Chapter 1, Foundations)
> in his book "Applied Cryptography" ;-):
>
> ...
> crypted[x] = plainBlock[x] ^ MD5pwd[streamMd5pwd] ;
> ...
>
> Best regards,
>
> Omar A. Herrera
>
> > -----Original Message-----
> > From: angelo@... [mailto:angelo@...]
> > Sent: Wednesday, February 15, 2006 2:48 PM
> > To: focus-linux@...
> > Subject: Kryptor Whitepaper released
> >
> > As I announced in previous threads, we released the full white paper of
> > the algorithm implemented in Kryptor
> > (http://www.rosiello.org/archivio/kryptor-0.1.2.tar.gz).
> >
> > The paper can be found at:
> > http://www.rosiello.org
> > or
> > http://www.rosiello.org/modules/smartsection/item.php?itemid=8
> >
> > cheers,
> > Angelo
> >
> > Rosiello Security,
> > http://www.rosiello.org