tools. In this regard, the search and development of
new methods for encrypting images that are close to
ideal are carried out. Increasingly, there are
publications that describe image encryption methods
implemented using cellular automata (CA)
technologies [3], [4], [5], [6], [7], [8], [9], [10]. In
these works, CA proved to be promising in solving
encryption problems.
2 Problem Statement
One of the main problems in solving the problem of
image encryption is the use of a long key gamma,
which can be generated by the user himself, or can
also generate a pseudo-random number generator
(PRNG) based on the established initial conditions.
Forming a key gamma for encrypting large amounts
of data (images) does not seem realistic. Therefore,
PRNG is most often used. However, PRNG cannot
always form the highest quality sequence of
numbers. In addition, the structure of the generator
may be known to other users. Such shortcomings
force developers to search for new more effective
methods.
A promising direction in solving such a problem
is the use of CA, on the basis of which PRNGs are
built, which showed a high quality of the generated
bit sequences, [3], [11], [12], [13], [14]. Elementary
CA (ECA) and two-dimensional CA are used, as
well as their states obtained during the formation of
evolution.
Despite the byte structure, bitmaps can be
considered as a sequence of two-dimensional bit
layers that can be encrypted both in parallel and
sequentially. To encrypt one two-dimensional N×M
bit array, it is necessary to use N×M key bits. If a
binary code of length K bits is used to encode the
visual characteristics of one pixel of a raster image,
then K × N × M key bits must be used to encrypt the
entire image. The use of PRNG based on CA
complicates the implementation of the encryption
method.
The paper solves the problem of implementing a
method for encrypting raster images using a key of
small length. To solve this problem, one ECA rule is
used, determined on the basis of experimental
studies.
Since a bitmap image is represented in a
computer system by a sequence of bytes or, more
precisely, a binary sequence, it is easiest to encrypt
images using the streaming encryption method [3],
[4], [5], [11], which consists in applying a bit key
gamma to a bitmap image [3], [4], [5], [6], [7], [8],
[9], [10], [11]. To implement this method, a device
for generating a key gamut is used, which, as a rule,
is a PRNG [12]. To date, a large number of PRNGs
have been developed [12], [13], [14], [15]. which
have different configurations. Almost all existing
PRNGs (mathematical, hardware, etc.) can be
simulated on a PC and implemented in software.
Using such a program model, you can encrypt any
graphic file. In papers [3], [10], [11], [15], methods
using this method are considered. In [11],
experimental studies were carried out and it was
shown that it is enough to encrypt the three most
significant bits of each color byte. In this case, a
pseudo-random bit sequence was used, generated by
a PRNG implemented on a CA with active cells,
[13], [14]. The obtained experimental results
showed a high quality of encryption. However, this
method takes time to form the key gamma and
complete enumeration of all bits that encode the
image.
There are image encryption methods based on
the Fourier transform, [16], [17], [18], and Wavelet
transform, [19]. In recent years, a direction based on
quantum image encryption has been developing
[21], [22], [23], [24]. Papers on these topics describe
complex encryption schemes that do not always
provide high quality encryption. In addition, such
approaches can lead to partial loss of information
about the original image at the decryption stage.
A large number of methods use various methods
based on chaos theory, [25], [26], [27], [28], [29],
[30]. However, these methods require complex
calculations and can lead to partial loss of
information.
There are methods using genetic algorithms,
[31]. [32], [33] [34], [35], DNA calculations, [36],
[37], [38], based on elliptic curves, [39], [40],
Rubik's cube, [41], and artificial neural networks,
[42]. All these methods require special calculations
to be performed to transform the information array
and form a key array, which limits these methods,
since they are not resistant to attacks and cannot
guarantee high reliability.
Image encryption methods using CA
technologies have been greatly developed [3], [4],
[5], [6], [7], [8], [9], [10]. Many of these works use
additional means for encryption. Often an additional
tool is chaos theory , [25], [26], [27], [28], [29],
[30]. There are also works that use separate ECA
rules with additional methods [7], [43]. Thus, in
[43], rules for an ECA with a length of 8 cells were
considered and studied. Rules that give a good result
are defined. However, the limited length of the ECA
does not give full grounds for asserting effective
encryption of color images. In [7], rule 30 is
considered, which does not provide high quality
image encryption. This is proven in paper [10]. In
WSEAS TRANSACTIONS on SYSTEMS and CONTROL
DOI: 10.37394/23203.2022.17.49