Kiberxavfsizlik asoslari

2. Asosiy qism. Simmetrik shifrlash usullarini axborotni himoyalashda ishlatish.

2.1. A5/1 shifrlash algoritmi haqida (oqimli)

GSM tarmog‘ida ovozli so‘zlashuvlarni shifrlash uchun foydalaniladi.

A5/1 oqimli shifrlash algoritmida 64 bitli 𝐾 kalitdan foydalaniladi.

A5/1 shifrlash algoritmi uchta chiziqli siljitish registorlaridan iborat bo‘lib, kiritilgan kalit 𝐾 ularga bo‘lib yoziladi:

𝑋 registor o‘zida 19 bit (𝑥₀,𝑥₁,…,𝑥₁₈)

𝑌 registor esa 22 bit (𝑦₀,𝑦₁,…,𝑦₂₁)

𝑍 registor esa 23 bit (𝑧₀,𝑧₁,…,𝑧₂₂)

Tasodifiy ketma-ketliklarni generatsiyalash

Berilgan uchta bit 𝑥₈,₁₀,𝑧₁₀ asosida 𝑚=𝑚𝑎𝑗(𝑥₈,𝑦₁₀,𝑧₁₀ ) funksiya qiymati hisoblanadi.

Masalan, (1,0,0)=0,𝑚𝑎𝑗(1,1,0)=1

Agar 𝑥₈=𝑚 ga teng bo‘lsa, 𝑋 siljitiladi:

𝑡=𝑥₁₃⨁𝑥₁₆⨁𝑥₁₇⨁𝑥₁₈

𝑖=18,17,16,…,1 uchun 𝑥_i=𝑥_(i-1)

𝑥₀=𝑡

Agar 𝑦₁₀=𝑚 ga teng bo‘lsa, 𝑌 siljitiladi:

𝑡=𝑦₂₀⨁𝑦₂₁

𝑖=21,20,19,…,1 uchun 𝑦_i=𝑦_(i-1)

𝑦₀=𝑡

Tasodifiy ketma-ketliklarni generatsiyalash

Agar 𝑧₁₀=𝑚 ga teng bo‘lsa, 𝑍 siljitiladi:

𝑡=𝑧₇⨁𝑧₂₀⨁𝑧₂₁⨁𝑧₂₂

𝑖=22,21,20,…,1 uchun 𝑧_i=𝑧_(i-1)

𝑧₀=𝑡

Shundan so‘ng tasodifiy ketma-ketlikning bir biti quyidagicha hisoblanadi:

𝑠=𝑥₁₈⨁𝑦₂₁⨁𝑧₂₂

Yuqoridagi ketma-ketlik ochiq matnni uzunligiga teng bitlarni generatsiya qilguncha takrorlanadi.

Bunga misol tariqasida Ismimning bosh harfini shifrlaydigan bo’lsam:

T = E

K = XORAZMIY

T = 0100

K = 0101100001001111010100100100000101011010010011010100100101011001

X: 0101100001001111010

Y: 1001001000001010110100

Z: 10011010100100101011001

1:

maj(0,0,0) = 0

X, Y va Z registorlar suriladi

t = = 1 0 1 0 = 0

t = = 0 0 = 0 t = = 0 0 0 1 = 1 X: 0010110000100111101 Y: 0100100100000101011010 Z: 11001101010010010101100 C = 1 0 0 0 = 1 2: maj(0,0,0) = 0 X, Y va Z registorlar suriladi t = = 1 1 0 1 = 1 t = = 1 0 = 1 t = = 1 1 0 0 = 0 X: 1001011000010011110 Y: 1010010010000010101101 Z: 01100110101001001010110 C = 0 1 0 1 = 0 3: maj(0,0,1) = 0 X, Y registorlar suriladi t = = 0 1 1 0 = 0 t = = 0 1 = 1 X: 0001011000010011110 Y: 1010010010000010101101 Z: 11001101010010010101100 C = 0 1 0 0 = 1 4: maj(0,0,0) = 0 X, Y va Z registorlar suriladi t = = 0 1 1 0 = 0 t = = 0 1 = 1 t = = 1 1 0 0 = 0 X: 0001011000010011110 Y: 1010010010000010101101 Z: 01100110101001001010110 C = 0 1 0 0 = 1 C = 1011