1.Considering the following plaintext message: The earth revolves around then sun.
a. If this message is sent unencrypted and successfully received, what is its entropy?
b. If this message is encrypted with DES using a random 56-bit key, what is the encrypted message's entropy?
c. If this message is encrypted with 3DES (using an optimal set of keys) what is the encrypted message's entropy?
2. The following ciphertext is a monoalphabetic ciper:
Vm gdeefl Pvdhbnptu, puq tfr lzpr mfch nfctrhm npt xf gfh mfc, puq lzpr mfc npt xf gfh mfch nfctrhm. Wfzt G. Qdttdxm
Decrypt this message, and briefly describe your cryptanalysis methodology. In particular, list features of the ciphertext that hindered or helped your decryption process.
3a. Bob picked N=91 for use in a RSA-encrypted message. Since N is part of the public key, Alice was able to crack Bob's message by determining the values of p and q that Bob used. What are the values of p and q did she determined?
b. Is 3,141,592,654 a prime number? Why or why not?
4. Bob is concerned about the possibility of having his 100k byte file modified without his knowledge, so he find outs a 128 bit hash. Alice, unbeknownst to Bob, changes a single character in Bob's file. Assuming that Bob used a strong hash function, what would the hash value of the modified file look like, as compared with the original hash value?
5. Bob receives an important signed message that was sent by Alice using a public key encryption system. Are there any circumstances or events that would allow Alice to successfully repudiate that she had sent the message?