# Re: RE: Kryptor Whitepaper released

*From*: angelo@xxxxxxxxxxxx*Date*: 15 Feb 2006 21:15:41 -0000

"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

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