ECE 646 – Fall 2004
Midterm Exam 2
December 4-5, 2004
Multiple-choice test
1. (0.5 pt) 1024-bit RSA can be securely used in the following block cipher
modes (choose as many as appropriate):
A. CBC
B. counter mode with j=64
C. CFB with j=1024
D. ECB
E. OFB with j=8
2. (0.5 pt) Assuming the use of classical algorithms for exponentiation,
multiplication, and modulo reduction, changing the length of the modulus
N from 512 bits to 2048 bits increases the time taken in software by the
RSA signature generation using Chinese Remainder Theorem by a factor
of:
A. 4
B. 8
C. 16
D. 32
E. 64
F. other
3. (0.5 pt) The number of the RSA messages not concealed by the RSA with
the public key equal to e=3, N=257*421 is equal to:
A. 9
B. 771
C. 1285
D. 216+1
E. 257*421
F. other
