Alice needs to send a private letter to Bob through an insecure communication channel. Describe an economic way against eavesdropper to protect the confidentiality of the letter. Assume that Alice and Bob donot have any pre-shared secret.

Question 1 a and b show work

1. Describe the steps of the Existential Forgery Attack against RSA Digital Signature as discussed in the class. Then answer whether it is possible for the attacker, Oscar, to create a message as he wishes with the correct signature signed by Bob. Why?

Alice and Bod have decided to use a symmetric encryption algorithm. They have some assumptions about their messages:- Messages only contain capital letters (i.e. A to Z)- The length of their shared key must be greater than or equal to the length of the plaintext- They assign each letter a number as follows: (A,0), (B,1), (C,2), (D,3),…, (Z,25)Their algorithm combines the key and the message using modular addition. The numerical values of corresponding message and key letters are added together, modulo 26. For example, if the plain text is “HELLO” and the key is “SECRET” then the encrypted message is calculated as following:Since the length of the plaintext is 5, we just need the first 5 letters of the key (i.e. “SECRE”), then for each letter, we should add corresponding letters in both the plaintext and the key modulo 26.Plaintext: H (7) E (4) L (11) L (11) O (14)Key: S (18) E (4) C (2) R (17) E(4)Cipher: Z (25) I (8) N(13) C(2) S (18) Write a program in Python, C/C++ or JavaScript to…