Madness #01 17 февраля 2001

Shifromaniya - cryptographic protection of information.

                SECURITY


  Dear readerz our
zine! You probably speculated that
exactly is hiding under the name of the
Article (Penal Code :->)? And all just to horrible-I was here 
recently nadybal tekstik interesting about standard algorithms 
for data encryption "we" and "them" and decided to put it on 
vseobshee rassmotrenie.Tak read it and enlighten. 

  By the way in the "Supplement" is a schematic diagram of a 
device for those individuals who can not wait to apply this 
knowledge to break into computers CIA, FBI, NSA, Secret Service 
'etc. This is called Mulka "GUBOZAKATALKA UNIVERSAL FIELD 
(BETA-version 1.0) " 


    Cryptographic protection of information.
(C) ??????????


    Cryptography - the science of protecting information from 
unauthorized reading it. Privacy Encryption is achieved, ie 
transformation, which are made secure trudnoraskryvaemymi input 
from the input data without special knowledge key information - 
the key. Understood by the key cryptosystem is easily editable 
part, kept a secret and determines which encrypt the 
transformation of the possible holds in this case. Cryptosystem

- The family selected using a key reversible transformations 
that convert the protected open text coded telegram and back. 

    It is desirable that the encryption methods
had at least two properties:

    - A legitimate recipient will be able to perform
inverse transformation and to decipher
message;

    - Cryptanalyst enemy interception of communications will 
not be able to recover on it the original message without such 
time and resources that will make this work work inappropriate.



1. Classification cryptosystem.


    By the nature of the use of certain key cryptosystems can 
be divided into two type: symmetric (single-key, secret-key) 
and asymmetric (open key).


    In the first case, the sender encoder and the decoder of 
the recipient uses the same key. Encoder forms a ciphertext, 
which is a function of the plaintext, the specific form of 
encryption is determined by the secret key. 

EDIT>> And now the same thing, but in russki.V
the simplest case, each character (or ASCII-code) in the open 
(source) text corresponds to the symbol in the ciphertext, and

shifrsimvol obtained from a source with a certain formula, and 
depends on the key or parolya.Kstati, not necessarily in 
different parts of the text to the same ref. character will 
match the same shifrsimvol.



  Recipient of the message decoder performs the inverse 
transformation of the same manner. The secret key is kept 
secret and transmitted the message sender the recipient through 
the channel which excludes key interception of enemy 
cryptanalyst. Usually expected to rule Kirchhoff: resistance

cipher is determined only by the secrecy
key, ie cryptanalyst knows all
details of the encryption and decryption
except the secret key.

    Open Text is usually arbitrary length if its size is great 
and it does not can be processed by a computing device encoder 
as a whole, it is divided into blocks of fixed length and each 
block is encrypted separately, regardless of its position in 
the input sequence. Such cryptosystems are called systems of 
block encryption. 

    In practice we usually use two general principles of 
encryption: the dispersion and mixing. Dispersion is to spread 
the influence of one symbol of plaintext to ciphertext many 
characters: this allows you to hide statistics properties of 
the plaintext. Development of this principle is to spread the 
influence of one character key for many symbols Shirograms that 
eliminates key recovery in parts. 

EDIT>> I think these things mean something like this: the text 
is divided into blocks and these blocks XOR-yatsya with each 
other and with the key. 


  Mixing is to use
encrypts these transformations, which
preclude the restoration of the relationship of the statistical 
properties of an open and ciphertext. Common way to achieve a 
good dispersion is to use a composite cipher, which can be 
implemented as a sequence of simple ciphers, each of which 
makes a small contribution to significant cumulative dispersion 
and mixing. As simple ciphers often use a simple substitution 
and transposition. 

  EDIT>> Who does not understand, using a cascade
encoding, encryption t.e.mnogokratnoe
different ciphers with different keys, a
divide the text into blocks and encoding
each block to its encryption.

    One of the best examples of cryptographic algorithm, 
developed in accordance with principles of diffusion and mixing

may be adopted in 1977 by the National Bureau of Standards U.S. 
Data Encryption Standard DES. Despite the intensive and 
thorough research of the algorithm specialists, has not been 
found vulnerable places the algorithm on which to base

would suggest a method of cryptanalysis,
significantly better than exhaustive search
keys. The general consensus is: DES - an exceptionally good 
cipher. In July 1991, enacted a similar domestic

Encryption Standard 28147-89.

    At the same time block codes have
significant drawback - they are propagated
errors that occur during transmission
messages through the communication channel. A single error in 
the ciphertext causes a distortion of about half of the 
plaintext by decryption. This requires the use of powerful 
error-correcting codes. 

    In block cipher, consisting of two identical
plaintext blocks are obtained by the same blocks of ciphertext. 
Avoid This allows stream ciphers, which

in contrast to the block, perform elementwise encryption data 
flow without delay in the cryptosystem. In general, each 
character of plaintext is encrypted, transmitted and decrypted 
independently of other characters. Otherwise, shifruyushee 
conversion element of the plaintext changes from one element to 
another, while for block ciphers Encryption transformation of 
each block remains unchanged. Sometimes the character of the 
plaintext can be encrypted with the limited number of 
characters preceding it. EDIT>> In short: a block cipher is a 
simple (or not simple: ->) XOR-ka, while for inline

each text a unique code generated sequence of equal length
original text (robust design, right? way analog
- The dynamic encoding of the register R)

    Stream ciphers based on pseudorandom key sequence -
generated in some way symbolic sequences with given
properties of unpredictability (randomness)
the appearance of another character. Generators
key sequences are usually based on combinations of shift 
registers and nonlinear Boolean functions. As

nonlinear Boolean function can be used Encryption DES, which 
corresponds to the use of DES in a mode output feedback (OFB) 
lil feedback ciphertext (CFB). The greatest interest is the 
mode of CFB, because in some cases OFB mode does not provide 
the required secrecy.


    Streaming encoding systems are close to
cryptosystems with a one-time key, which key size is the size 
of encrypted text. When cryptanalysis based known-plaintext 
stability of the system is determined by the nonlinearity of 
Boolean functions that allows to estimate the cryptographic 
strength of the system based on an analysis of the form used 
functions. Consequently, flow ciphers, in contrast to other 
cryptosystems is much more a test secrecy. In addition, 
streaming encoding systems is no error propagation, or it is 
limited. For these reasons and also because of the high speed

processing streaming encoding systems
cause a lot of trust of many consumers and professionals.

    In public-key cryptosystems in
algorithms for encryption and decryption use different keys, 
each of which can not be obtained from the other (with 
acceptable cost). One key is used to encrypt, the other - for 
decryption. The basic principle of public key

based on the use of unilateral
functions or irreversible and unilateral
functions with a trapdoor (hiding course).
EDIT>> Who knew-mail me, I'll put you
Monument :-))))))

    Calculation of key messages by the recipient, who shall 
retain the key that he would later use (ie secret key). Another 
the key messages he sends to the sender - public key - not 
being afraid of his publicity. Using this public key, any party 
can encrypt the text and send it recipient who has generated 
this public key. All the algorithms used

publicly available. It is important that the encryption and 
decryption are reversible only if when they are provided 
strictly interconnected by a pair of keys (public / private) 
and public key must be an irreversible feature of the secret

key. Similarly, the ciphertext should
is an irreversible feature of the plaintext that is 
fundamentally different from encryption system with the secret 
key. 

    The study of irreversible functions carried out mainly in 
the following areas: discrete exponentiation - algorithm DH 
(Diffie-Hellman), the multiplication of prime numbers - the 
algorithm RSA (Rayvest, Shamir, Adleman), the use of 
error-correcting codes, Goppa problem of NP-completeness, in 
particular cryptalgorithm Merkle and Hellman based on "the 
problem of packing a knapsack, open Shamir, and several others 
caught legkoraskryvaemymi and unpromising. 

    The first system (DH) provides public key distribution, ie, 
eliminates the transmission of secret keys, and is today 
considered one of the most persistent and convenient systems

public key. Reliability of the second method
(RSA) is in direct proportion to the
the complexity of the expansion of large numbers into factors. 
If the factors have a length of order 100 decimal digits, the 
best known ways of factoring needs about 100 million years of 
machine time, the same encryption and decryption requires the 
order of 1-2 per unit. NP-complete problem is well known in 
combinatorics and are in general extremely difficult, but to 
construct the corresponding cipher is very easy.


    In systems with a public key, as well
as a block cipher, requires a sound
size of the encrypted block, although, perhaps,
no greater than in the algorithm DES, which prevents, along 
with low-speed encryption using public-key algorithms in stream 
ciphers. To date, high-performance systems with the public key 
is not found. Almost universally, accepted limit the use of 
public-key cryptosystems - only for managing keys and digital 
signatures. 



    2.1 DES-USA standard for data encryption.


    Cryptography has been known since ancient
times (enough to remember codes Caesar)
and until recently remained a privilege of only government and 
military agencies. The situation changed dramatically after the 
publication in 1949 of the book of Shannon "The work on 
information theory and cybernetics." Cryptography has become 
the object of attention of many scientists. Adoption standard 
DES encryption was a powerful impetus to the widespread use of 
encryption commercial systems. The introduction of this 
standard - a great example of unification and standardization 
of the remedies. An example of a systematic approach to create 
a single large-scale information security system is the 
directive of the Ministry of Finance of the USA 1984, under 
which all public and private organizations conducting business 
with U.S. government must implement a procedure for encrypting 
DES; largest banks Citibank, Chase Manhattan Bank, Manufaktures 
Hannover Trust, Bank of America, Security Pacific Bank also 
implemented this system. 

    U.S. Department of Energy has more than 30 active networks,
which uses an algorithm DES, Ministry of Justice, 20,000 radio 
sets that have the means of protection based on DES. 
Standardization has recently acquired an international 
character, confirmation of this - the international standard 
ISO 8372 in 1987, developed based on the cryptographic 
algorithm DES. 

    As standard equipment the encryption can be called a device 
Cidex-NH, based on the algorithm of DES; rate

Encryption - from 56 Kbps to 7 Mbps. Commercially available 
self-encryption DES block 2000, it is also used

procedure encryption DES; encryption speed - from 38.4 Kbps to 
110 Kbps. In various sectors of commercial activity is used 
processor data encryption / decryption FACOM 2151A, based on 
algorithm DES; rate - from 2.4 kbps to 19.2 Kbps. With the 
proliferation of personal computers for the most effective They 
have security software. For example, developed a software 
package for encryption / decryption of information CTA 
(Computer Intelligence Access), implements the algorithm of 
DES. The same algorithm used in package SecretDisk (CF Systems) 
to prevent unauthorized access to the disks. 

    Thus, the DES algorithm is the main mechanism used by 
private and public agencies to protect U.S. information. At the 
same time the National Security Agency, acting as an expert on 
cryptography algorithms, developing new algorithms

data encryption for the masses. In 1987, National Bureau of 
Standards after the discussion confirmed the validity of DES; a 
revision scheduled to be held no later than January 1992 and to 
date, DES action is limited solely by commercial systems. 


          <TO BE CONTINUED>