MATH/CMSC 456 (Washington)
Exam 1 Solutions
March 13, 2014
1. (15 points = 10+5) (a) Let the plaintext be AAAAA. This is the vector (0,0,0,0,0).
When this is added to the key vector, the ciphertext is the key.
(b) This is a Vigen`re system with key length

MATH/CMSC 456 (Washington)
Exam 1
March 13, 2014
There are 5 pages. Do each problem on the page containing the problem. You may use
the back of the page if necessary. Parts (a), (b), (c) of a problem are not necessarily
related.
a
0
b
1
c
2
d
3
e
4
f
5
g

MATH/CMSC 456 (Washington)
Exam 1 Solutions
March 13, 2014
1. (20 points = 8+7+5) (a) With displacement of 1, there are 4 matches. With a
displacement of 2, there are 11 matches. With a displacement of 3, there are 4 matches.
So the key length is probably

MATH/CMSC 456 (Washington)
Exam 1
March 13, 2014
There are 5 pages. Do each problem on the page containing the problem. You may use
the back of the page if necessary. Parts (a), (b), (c) of a problem are not necessarily
related.
a
0
b
1
c
2
d
3
e
4
f
5
g