정보보호입문 Brute Force Attack

목차

1. Task1(Required) Write down a cryptanalytic(or breaking) algorithm using the Brute-Force Attack.
2. Task2(Required) Write down a cryptanalytic(or breaking) algorithm using English Aphabet Frequency Table.
3. Task 3(Optional with extra credit)
4. Task 4(Optional with extra credit)

본문내용

Task1(Required) Write down a cryptanalytic(or breaking) algorithm using the Brute-Force Attack.

Brute-Force Attack on Caesar Cipher Algorithm:
Initial State: Ciphertext
Input: Ciphertext of English Alphabet = { C1, C2, …., Cn } and Unknown Key k
Step 1 : Yi <- Ci
Step 2 – 2 : Yi <- (Xi – k0) mod 26
If (Xi – k0) >= 0 Then Yi <- (Xi – k0) mod 26
If (Xi – k0) < 0 Then Yi <- (26 + Xi - k0) mod 26
If, 해석 가능한 문장이 나오면 Stop
Step 2 - 1 : Yi <- (Xi – k1) mod 26
If (Xi – k1) >= 0 Then Yi <- (Xi – k1) mod 26
If (Xi – k1) < 0 Then Yi <- (26 + Xi - k1) mod 26
If, 해석 가능한 문장이 나오면 Stop

<중 략>

Brute-Force Attack
Step 1 : For each of K ={0, …, 25}
Substep 1) For all I = 1, 2, …, n
Substep 1-1 : Xi <- Ci
substep 1-2 : Yi <- (Xi – k) mod 26
substep 1-3 : Pi <- Yi
SubStep 2) Ask user if this {P1, …, Pn} is correct
Substep 3) If answer = “yes” then return {P1, …, Pn}

참고 자료

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