## CryptoDB

### Boris Ryabko

#### Affiliation: Siberian State Univ-Telecomm. & Comp. Sci

#### Publications

**Year**

**Venue**

**Title**

2006

EPRINT

Provably Secure Universal Steganographic Systems
Abstract

We propose a simple universal (that is, distribution--free) steganographic system
in which covertexts with and without hidden texts are statistically indistinguishable.
Moreover, the proposed steganographic system has two important properties. First, the rate of transmission of hidden information approaches the Shannon entropy
of the covertext source as the size of blocks used for hidden text encoding tends to infinity.
Second, if the size of the alphabet of the covertext source and its minentropy tend to infinity
then the the number of bits of hidden text per letter of covertext tends to $\log(n!)/n$ where $n$
is the (fixed) size of blocks used for hidden text encoding. The proposed stegosystem uses randomization.

2006

EPRINT

The experimental distinguishing attack on RC4
Abstract

The output of RC4 was analyzed using the "book stack" test for
randomness. It is experimentally shown that the
keystream generated from RC4 can be distinguished from random with
about $2^{32}$ output bits.

2002

EPRINT

Adaptive chi-square test and its application to some cryptographic problems
Abstract

We address the problem of testing the hypothesis H_0 that the
letters from some alphabet A= {a_1,a_2,..., a_k }, are
distributed uniformly
against the alternative hypothesis H_1 that the true
distribution is not uniform, in case k is large. (It is typical
for random number testing and some cryptographic problems where
k= 2^{10} - 2^{30} and more). In such
a case it is difficult to use the chi-square test because the
sample size must be greater than k.
We suggest the adaptive chi-square test which can be
successfully applied for testing some kinds of H_1 even in case
when the sample size is much less than k. This statement is
confirmed theoretically and experimentally. The theoretical proof
is based on the consideration of one kind of the alternative
hypothesis H_1 where the suggested test rejects the null
hypothesis when the sample size is O( \sqrt{k} ) (instead of
const k for the usual chi-square test ).
For experimental
investigation of the suggested test we consider a problem of
testing ciphered Russian texts. It turns out that the suggested
test can distinguish the ciphered texts from random sequences
basing on a sample which is much smaller than that required for the
usual chi-square test.

2001

EPRINT

The simple ideal cipher system
Abstract

We address the problem of how to construct ideal cipher systems when the
length
of a key is much less than the length of an encrypted message. We suggest a
new
secret key cipher system in which firstly the message is transformed into two
parts in such a
way that
the biggest part consists of independent and equiprobable letters.
Secondly the relatively small second part is enciphered wholly by the Vernam
cipher
whereas only few bits from the biggest part are enciphered.
This transformation is based on the fast version of the Elias
construction of an unbiased random sequence.
The
time required for encoding and decoding and the memory size of the encoder and
decoder are presented as functions
of the ratio of the key length and the message length.
The suggested scheme can be applied to sources with unknown statistics.

#### Coauthors

- Sergey Doroshenko (1)
- Daniil Ryabko (1)