(6 points) Vernam cipher (a) Consider the following letter encodings: A=000 E=001 H=010 J=011 L=100 N=101 O=110 T=111 a)A message M = HOTEL is Vernam encrypted into ciphertext C = NOJTE. Find the co

2) (6 points) Vernam cipher

1. Consider the following letter encodings:

A message M = HOTEL is Vernam encrypted into ciphertext C = NOJTE. Find the corresponding encryption key (note that it should be 5 letters long). Provide details of your cryptanalysis. Vague answer will not be accepted.

A=0

E=1

H=2

J=3

L=4

N=5

O=6

T=7

M=HOTEL C=NOJTE

26714 56371

M+K=C

K=C-M

K=(5,6,3,7,1) – (2,6,7,1,4)

K=(3,0,-4,6,-3)

Total number of letter encodings =8 therefore adding 8 to the negative numbers

K=(3,0,4,6,5)

K=JALON

Encryption key = JALON

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(b) Consider the following two ciphertexts C1= TAHNNL and C2=EOEOEA that are obtained by Vernam encrypting messages M1 and M2, respectively, using the same encryption key. The letter encodings is the same as shown in Step (a). The encrypted messages are two English names. Let mi,k be the kth letter in the message Mi.

The following is known about the messages (names): m1,2 = A and m2,5 = N. Using this limited information, try to recover messages M1 and M2, as well as the encryption key. Provide details of your cryptanalysis. Vague answer will not be accepted