Consider the case of Alice sending a message, m, to Bob. Both Alice and Bob use public key cryptography and each has a public and private key as described in the text.  The figure attached below shows the operations that Alice must perform to provide confidentiality, authentication, and integrity when sending a message to Bob over the network. We can use either symmetric key or public key cryptography to encrypt a message.  For our purposes, either technique will encrypt the message, and applying both doesn't make it "more secure".  Also, we can assume that the session key would remain a secret so the fact that it is discarded does not make it "more secure".  Why do we use a session key, Ks, instead of relying only on public key Cryptography?  In other words, why do we use both public key and symmetric key cryptography?

A secure email system is expected to provide confidentiality, sender's non-repudiation, and message integrity. Alice uses three keys to achieve this goal. The three keys are Alice's private key (KA), Bob's public key (Kg), and a randomly generated symmetric key (Ks). The encryption procedure is shown below: How can Bob 1) decrypt the data, 2) verify the message's integrity, and 3) verify the sender's non-repudiation? Describe the detailed steps (including the formulas) and show your work. KA m H(-) KA( m I am using SHA-256 KA(H(M)) Ks() KB(*) K Ks K.(m, KA(H(m)) + + KB(Ks) Internet 34

I need help with the following problems in cryptography. A. Encrypt the message “Freedom” using the Playfair matrix M F H I K U N O P Q Z V W X Y E L A R G D S T B C T B. Construct the Playfair matrix with the keyword “LARGEST” and encrypt the message “Freedom” again. C. Compare the results obtained in A and B. How do you account for these results?

. Q: There is no authentication in the Diffie-Hellman key-exchange protocol. By exploiting this property, a malicious third party, Chuck, can easily break into the key exchange taking place between Alice and Bob, and subsequently ruin the security. Explain how this would work.

The definition of a Shift Cipher can be expressed as follows:Def. Let x, y, k ∈ Z26 with the encryption operation as ek(x) ≡ x + k mod 26 and thedecryption operation as dk(y) ≡ y - k mod 26.Given the provided letter encoding, what would be the encoding of the plaintext word ATTACKafter applying a shift cipher with a k=17?

In this problem we explore the relationship between password length and cryptographic security. Suppose a password consists of 77 ASCII characters. You can review the ASCII characters here.. Exactly 27=12827=128 of these codes are for printable characters; we will assume every character in the password is printable. What is the size of the keyspace that consists of passwords of this form?What is the equivalent key length in bits?  Assuming that you could check one password every 10−810−8 seconds, what is the worst case running time for cracking this password by brute force search (in days)? Now assume that the user used only 3131 characters from the keyboard. What is the key length in bits in this case?  How many days, in the worst case, would it take to break this weaker password? You can't round to the nearest day here -- be as exact as possible.  Supposing you used only 3131 characters, how long is the shortest password that achieves 252252 bits of security?

The notation from this problem is from Understanding Cryptography by Paar and Pelzl. Consider the LFSR represented by the polynomial x^4+x^3+x+1. What are the tap bits of the LFSR? Please enter your answer as unspaced binary digits (e.g. 010101 to represent p5=0,p4=1,p3=0,p2=1,p1=0,p0=1

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…

Each of the following is a true/false statement about a tweakable block cipher (TBC). Place a checkmark next to each true statement. In the questions mentioning E', let E' be a random instance of a TBC and E'(T,X) be the result of using E' with tweak T and input X. Group of answer choices: (1)For TBC security both the current key and tweak in use must be kept secret from adversaries. (2)Each time a new tweak is given to a TBC, the TBC behaves like a new random permutation. (3)When a TBC is used once per tweak its outputs may be considered (4)A TBC is a prominent part of the design of OCB. (5)If X1 ≠ X2, then always E'(T,X1) ≠ E'(T,X2) (6)If T1 ≠ T2, then always E'(T1,X) ≠ E'(T2,X)