ssd2 / Exam 3 Practical / 3

3. Advanced Encryption

1. Consider the alphabet shift cipher. Complete the following table:

   Plaintext	Encryption Technique	Ciphertext
   Secret	Shift left by 1 character	Rdbqds
   Message	Shift left by 2 characters	Kcqqyec

2. Explain how the passphrase encryption method works and why it is a stronger encryption method compared to the alphabet shift cipher encryption?

Even if the person knows the word he can’t understand the meaning, because that is the shift of the alphabet.

3. What is the encrypted message for "Under the tower" using the passphrase "ABC".

Plaintext Under the tower Key ABC Copied Key ABCAB CAB CABCA Key Converted to Numbers 1 2 3 1 2 3 1 2 3 1 2 3 1 Plaintext U n d e r t h e t o w e r Ciphertext V P G F T W I G W P Y H S Answer: I can use a public key to decrypt the digital signature and I see the hash of the message. I can then compute the hash of the message. If the two hash codes were the same, the message had not been altered.

4. How does a sender include a digital signature?

People in whom you trust and who dose not send spam, if you sent something important, and it should open it.

5. How does a receiver verify that a digitally signed message is genuine.

He compare open key.

To protect against this scenario, an authentication system can be set up between the user's applicationand the signing application. The general idea is to provide some means for both the user app and signing app to verify each other's integrity.