- Times: 2 hours Max. Score: 100 1. Fill-in-the-Blank(20 marks) (discrete logarithm, integer factorization, encryption, decryption, key, plaintext, ciphertext, asymmetric encryption, symmetric encryption, one-way function) From the above list of the words, select appropriate ones to fill in the blanks in the following definitions. (1)The process of converting information from one form (usually human readable), into another form (not usually readable) is called The process of converting Information from one form (not usually haman readable), into another form (usually human readable) is called The message which is human readable is called whille an encrypted information unreadable is An external piece of information used in the encryption and decryption process is called (2) uses the same key for encryption and decryption while uses different keys for encryption and decryption. (3)The security of RSA sryptosystens depends on the problem of The security of Elgamal encryption cryptosystem depends on the problem; (4) A function f(x) is called If the compatation y=f(x) is efficient but the inverse computation x=f1(y) is hard. 2. Computations (20 marks, 4 marks for each) (1) 35mod8= ; 98 mod 12= (2) (18+35)mod11= ; (140-29) mod 13= (3) 1312mod10= :2319mod11= (4) 323mod7= (5) (19)= (21)= 3. Single Choise( 10 marks, 2 marks for each) (1) In Shift Cipher, if the plaintext d is encrypted to be L, the ciphertext of plaintext g is ( ) A.0B.PC.QD.N (2) DES has ( ) rounds- A. 10 B.12C.16D.64 (3) In DES, the input of S box S1 is x=100000, the output S1(x) of ) A. 1000 B. 0100 C. 0010 D. 0110 (4) Each block of AES has ( J bits. A. 64 B. 56 C. 128 D. 256 (5) Symmetric ciphers are divided into stream ciphers and ( ) ciphers. A. public-kay B. classical C. shift D. block 4. Computation II (write the process, 20 marks, 10 marks for each) (1) ged (13,55); ged (15,99) (2) 191mod42 5. In RSA, a =55, e-23, compete the private key d using extended Euclidean algorithm, and decrypt the ciphentext ywz. (10 marks) 6. Write the properties of Hash function. (10 marks) 7. Describe the Diffie-Heliman key exchange protocol. (10 marks)