The Feistel cipher is a symmetric block cipher encryption framework which is the basis of many modern day encryption algorithms. In this coursework you will implement a Feistel cipher system as a hardware component and as a software implementation. In a Feistel cipher the plaintext, P, to be encrypted is split into two equal size parts Lo and Ro such that P with a key, and the result is XOR'd with the other half of the plaintext. Feistel ciphers often employ multiple rounds of this scheme. In general the scheme works as follows, for all i = 0, . .. ,n, Lo Ro. A function F is applied to one half of the plaintext, combined L+1 = R; R4+1 = L, & F(R, K;) To decrypt an encrypted message using this cipher we can apply the same procedure in reverse. For i = n, n – 1, .,0, R, = L,+1 L; = R.-1 © F(L+1, K.) For this coursework we are interested in the 16-bit Feistel cipher which uses 4 rounds. The function F(A, B) = AÐB. The keys are derived from a single 8-bit key Ko such that, %3D Ko = b,bebzb4b3b2bībo K1 = bsbzbab3b2b,bob, K2 = b;b,bzb½b,bobyb6 K3 = b4b3b2b,bob7bebs

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Alice sets up an RSA public/private key, but instead of using two primes, she chooses three primes p, q, and r and she uses n=pqr as her RSA-style modulus. She chooses an encryption exponent e and calculates a decryption exponent d. Encryption and Decryption are defined: C ≡ me mod n and m ≡ Cd mod n where C is the ciphertext corresponding to the message m.  Decryption: de ≡ 1 mod φ(n) | Let p = 5, q = 7, r = 3, e = 11, and the decryption exponent d = -13. n = 105 & φ(n) = 48 Q: Alice upgrades to three primes that are each 200 digits long. How many digits does n have?

Design a cryptographic solution for implementing the dinning cryptographers protocol.  You should consider the following: The secret messages shared between any two agents in the protocol are communicated over public channels only. The announcements made by each agent must be traceable in a trustworthy way to that agent.   Your solution should be a new protocol that addresses the above two requirements.

Computer Science Assume we use transposition cipher to encrypt the data, and the original message is stored in a 8 by 5 matrix (8 rows and 5 columns). If the ciphertext is shown below, what is the original plaintext?WMHPSCATEEEUCELELTCTIASLOTMRNCA

Suppose your RSA public key is PK: {n, e} = {13861, 37}. Your friend sends you a ciphertext C = 9908. But unfortunately you have forgotten your private key, now you have to crack it yourself.a) Write down a possible condition of factors p and q.p= q=b) What is your private key SK: {d}?d=c) What is the plaintext of your friend’s message?The plaintext M =d) Suppose the plaintext M is a 12-digit number consisting of a prefix “19” and 1234567890. What is the corresponding ciphertext? Since M is greater than n, you only need to encrypt four digits at a time. Ignore redundant zeros. e.g., 0001 = 1. The result should contain three integers.The ciphertext C0 =

A ciphertext has been generated with an affine cipher. The most frequent letter of the ciphertext is “F”, and the second most frequent letter of the ciphertext is “C”. Break this code by figuring out the key numbers. Hint: Based on the letter frequency, E is the most frequent letter and T is the second most frequent letter. Therefore, F should be the ciphertext of E and C should be the ciphertext of T.