Author:
Minnie Fisher

A 2,000-bit message is used to generate a 256-bit hash. One the average, how many other messages could be expected to generate the same hash value?

1. A 2,000-bit message is used to generate a 256-bit hash. One the average, how many other messages could be expected to generate the same hash value? What does this tell us about the length of a hash as compared to the length of the message?2. Using the English alphabet (i.e., mod 26 arithmetic) let plaintext = {p1, p2,… , pn} and corresponding ciphertext = {c1, c2,… , cn}. Suppose the encryption function is ci = pi + 5 (mod 26). If you receive the ciphertext message RNQJDHDWZX, decrypt to recover the plaintext. What is the decryption function, and the recovered plaintext? What type of cipher is this? What are some weaknesses of this cipher?3. Substantiate or refute the following statement: The cryptographic basis of the Enigma machine is the use of a trapdoor function.4. Consider the following plaintext message: THE BOILING POINT OF WATER IS 212 DEGREES FAHRENHEIT.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?5. A particular cipher is implemented by combining the ASCII representation of plaintext characters with pseudorandom bytes (eight-bit binary strings of 1s and 0s) using the XOR function. In the process of encrypting a message, a character in the plaintext, a capital R, is XORed with the pseudorandom byte 10010101.a. What is the ciphertext (in binary form) generated by the encryption of the character R? (Please show your work.) b. How is the plaintext for this encrypted R recovered? (Please show your work.)6. The following ciphertext is a monoalphabetic ciper: ROXBOOG TOSOXUXUVG WGP NVTMOXXUGM, UX UE W HWTCOI XLWX W GOB XLVDMLX OCOT EXTDMMIOE UGXV OAUEXOGQO. HWEVG QVVIOZDecrypt this message, and briefly describe your cryptanalysis methodology.

Tutorial