Solve:

12 mod 5

Alice replaces each letter with the one three positions forward (A → D).

What cipher is being used?

During a secure transaction, an attacker captures encrypted data packets between a bank and a customer. Later, they resend these exact packets to the bank to trick it into processing a duplicate payment.

Which type of attack is this?

A user downloads a software update. The update is signed with the developer’s private key, and the user’s system verifies the signature using the developer’s public key. After installation, the software behaves as expected.

Which security goals are demonstrated?

Solve:

17  mod 13

A user logs into their email using a password. The system stores passwords as plaintext. An attacker steals the database and reads all passwords.

Which security goal is missing?

PayPal sends digitally signed receipts to confirm transactions.

Which goal is ensured?

Two-factor authentication for Microsoft accounts prevents unauthorised access.

Which goal does it reinforce?

WhatsApp allows only sender and receiver to read messages.

Which type of attack does this prevent?

Solve:

4² mod 11