Question

If a cryptanalyst only knows the encryption algorithm and ciphertext, then which type of attack can be performed by him?

• A. Known Plaintext Attack
• B. Ciphertext Only Attack
• C. Chosen Plaintext Attack
• D. Chosen Text Attack

Hint:

A Ciphertext Only Attack is the most difficult type of cryptanalytic attack since the attacker only has access to the encrypted message.

Answer 1

The Correct Option is B

Step 1: Understanding the attack types.
A Ciphertext Only Attack is when a cryptanalyst has only the ciphertext and not the corresponding plaintext. This is the type of attack where only the encryption algorithm and ciphertext are known.

Step 2: Analysis of options.
- (A) Known Plaintext Attack: This requires the cryptanalyst to have both ciphertext and the corresponding plaintext.
- (B) Ciphertext Only Attack: This attack uses only the ciphertext, which fits the given conditions.
- (C) Chosen Plaintext Attack: This requires the cryptanalyst to choose the plaintext and encrypt it.
- (D) Chosen Text Attack: This is similar to the Chosen Plaintext Attack, but involves the cryptanalyst choosing both plaintext and ciphertext.

Step 3: Conclusion.
The correct answer is (B) Ciphertext Only Attack.