ECE 646 – Fall 2002Multiple-choice testA. 2C. 4712Short problemsECE 646 – Fall 2002 Multiple-choice test 1. (1 pt) The ciphertext character frequency shown in the attached figure most likely corresponds to the following cipher A. ENIGMA B. Vigenère cipher with the period d=1 C. shift cipher with k=25 D. running-key cipher E. affine cipher with k1=1 and k2=0 F. Playfair cipher with the key “ABCDEFGHIJKLMNOPRSTUVWXYZ” 02468101214abcde fghI j k lmnopqrs t uvwxyz Standard English character frequency 02468101214abcde fgh I j k lmnopqrs t uvwxyz Ciphertext character frequency2. (1 pt) In the ciphertext obtained using Vigenère cipher, a four-character sequence QBCR appears at positions 4, 34, and 49. Additionally, the measure of roughness for this ciphertext is equal to 0.012. Based on this information, the most likely period of the Vigenère cipher is: A. 2 B. 3 C. 5 D. 10 E. 15 F. 30 3. (1 pt) Increasing the number of rotors in ENIGMA from 3 to 5 in May 1938 increased the amount of effort necessary to find the correct settings of the machine by a factor of: A. 5/3 B. 3 C. 5 D. 10 E. 20 F. 60 4. (2 pt) Arrange the following ciphers: a) according to the number of distinct keys (starting from the cipher with the smallest amount of keys) b) according to the amount of computations necessary to break the cipher using the best available practical method (starting from the cipher that requires the smallest amount of computations). A. Triple DES EDE with two keys K1 and K2 (assuming access to the first 16 bytes of the plaintext and the corresponding ciphertext) B. Double DES (assuming access to the first 16 bytes of the plaintext and the corresponding ciphertext) C. Playfair cipher (assuming access to the first 100-letters of the ciphertext) D. Vigenère cipher with the period d=5 (assuming access to the first 500 letters of the ciphertext) E. RC5 32/12/7 (assuming access to the first 16 bytes of the plaintext and the corresponding ciphertext) 5. (1 pt) Match the following numbers into four pairs of mutual inverses modulo 13. A. 2 B. 3 C. 4 D. 7 E. 9 F. 10 G. 12Short problems 1. (3 pt) Encrypt the message "UNIVERSITY" using the Vigenère cipher with the key "GMU". 2. (3 pt) Compute bits number 2, 31, 34, and 63 at the output of the first round of the DES encryption, assuming that the plaintext block is composed of all ones and the first round key K1 is equal to F0F0F0F0F0F0 in the hexadecimal notation. (3 pt) Given below are the internal keys used during the first full round of IDEA during encryption. What are the values of the corresponding internal keys used during decryption (these keys are computed based on the listed below internal keys and are used during the last round and the output transformation of the decryption): Ka= 0800 Kb= BABE Kc= 0000 Kd= FFFF Ke= 6398 Kf=
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