THE 3
rd
INTERNATIONAL SCIENTIFIC CONFERENCES OF STUDENTS AND YOUNG RESEARCHERS
dedicated to the 99
th
anniversary of the National Leader of Azerbaijan Heydar Aliyev
216
Cryptographic algorithms are mainly categorized into two classes:
Symmetric (DES, 3DES, AES) and Asymmetric (RSA).
Symmetric
cryptographic algorithms (or secret-key) use the same cryptographic key to
encrypt and decrypt data, while asymmetric algorithms (or public-key) require
different keys for encryption and decryption.
DES.
Data Encryption Standard (DES) is a symmetric algorithm,
designed by IBM cryptographers, encrypts text in a 64-bit block, using а 56-
bit key. The encryption algorithm consists of three stages: firstly, bitwise
permutation IP is performed and the initial 64-bit
text is split into Left and
Right halves, L
0
and R
0
,
respectively. Then, these halves go through 16
iterations of a particular function
f
that includes permutation and substitution
phases. In each of the 16 iteration rounds, a different subkey
𝑘
is used that
is derived from the main 56-bit key. This process can be expressed using the
following equations:
𝐿 = 𝑅 − 1
𝑅 = 𝐿 − 1 𝑋𝑂𝑅 𝑓 (𝑅 − 1, 𝑘 )
where
f
is a function and
𝑘
is a subkey in round i. Lastly, the
final permutation
IP
-1
(the inverse of the initial permutation IP) is executed to achieve ciphertext.
DES had been widely used for an approximately 25-year period until the
1990s, but, modern devices, such as Deep Crack and COPACOBANA, can
decrypt it with a brute-force attack in a few days. To eliminate the drawbacks
of DES, a new algorithm,
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