# Re: potential break or real break?

On 2 Feb 2007 08:17:22 -0800, jt64@xxxxxxxx wrote:

At least i think this is true for let us say a 256 bit key and a 256
byte permutation like my simplistic cipher STREAMBUDDY, i don't think
it is a stream cipher it is a PNG based on "nonereversible/hard to
reverse" byte walks, creating two stream that is downmixed by XOR into
one stream, and then further obfuscated by XOR with and older round of
the combinatorial XOR shuffles.
If your key is 256 bits long, then your algorithm can only produce
2^256 different keystreams. If it produced more than 2^256 then the
algorithm would not be reversible and it would not work correctly as a
cypher.

This allows an attacker to try every possible key, generating every
possible keystream and seeing what sort of plaintext results. A
simple statistical analysis of character frequencies will tell when an
interesting decryption is found. That is a brute force attack, and
every cypher with a fixed size key is vulnerable to it, no matter how
the keystream is generated.

OTP is not vulnerable because the key (not the keystream) is as long
as the plaintext so a brute force attack just produces all possible
plaintexts with that length, from "aaa ... aaa" to "zzz ... zzz", with
no way for the attacker to tell which message is the correct one.

rossum

.

## Relevant Pages

• Re: potential break or real break?
... byte permutation like my simplistic cipher STREAMBUDDY, ... creating two stream that is downmixed by XOR into ... possible keystream and seeing what sort of plaintext results. ... as the plaintext so a brute force attack just produces all possible ...
(sci.crypt)
• Re: potential break or real break?
... Because your keystream is generated by an algorithm and thus cannot be ... Your algorithm is a stream cypher because the keystream is generated ...
(sci.crypt)
• Re: Encryption key longer than text to encrypt
... stream cipher where the keystream generation is independant from the ... In such a context, the OTP key and the keystream share the same idea, ... Hence there are 2**128 different keystreams possible in this cypher. ...
(sci.crypt)
• Re: Chosen plaintext attacks
... attack the underlying CSPRNG directly. ... plaintext will be revealed. ... It was slopy written of me of course i meant the the keystream, ... But this discussion is NOT about OTP but about stream cyphers. ...
(sci.crypt)
• Re: simple encryption
... >> It only has one constructor, and it NEEDS some type of stream! ... As I said before, encryption fundamentally revolves around ... > binary data, not text. ... > from text to binary and the reverse before doing anything else. ...
(microsoft.public.dotnet.languages.csharp)