Problem #1 Given below is a well-known cryptosystem called affine Caesar cipher, as well as some ciphertext generated using the affine Caesar cipher. P = C = Z 26 = {0, 1, 2, ..., 25}; K = {(a, b) Z26 Z26 | gcd(a, 26) = 1} y = E([a,b], x) = (ax + b) mod 26, x = D([a,b], y) = a-1 (y – b) mod 26, where x P, y C. Ciphertext sample: VPWOMFUWOFMYMHUNWBBWGCRVVPSFVPUTHUJWMC OMFUOVSVWOVWGSRSFSREOWOQMHKOBMHVPWOUFG HETVWMFOEOVUYVMMZCVGSFEMCCOUEMCHKFMQRU NIUMBRWFUSHSRIUZHSVMBWFNVPUOUGHUVKUEVM MVPUFEMCQWRRPSJUVHCREGHSGKUNVPUOEOVUY For this problem, please do the following: (a) provide an analysis detailing its strength/weakness; (b) attempt to uncover the plaintext associated with the ciphertext; (c) attempt to determine the secret key (a, b) used.
Problem #1
Given below is a well-known cryptosystem called affine Caesar cipher, as well as some
ciphertext generated using the affine Caesar cipher.
P = C = Z 26 = {0, 1, 2, ..., 25};
K = {(a, b) Z26 Z26 | gcd(a, 26) = 1}
y = E([a,b], x) = (ax + b) mod 26,
x = D([a,b], y) = a-1 (y – b) mod 26,
where x P, y C.
Ciphertext sample:
VPWOMFUWOFMYMHUNWBBWGCRVVPSFVPUTHUJWMC
OMFUOVSVWOVWGSRSFSREOWOQMHKOBMHVPWOUFG
HETVWMFOEOVUYVMMZCVGSFEMCCOUEMCHKFMQRU
NIUMBRWFUSHSRIUZHSVMBWFNVPUOUGHUVKUEVM
MVPUFEMCQWRRPSJUVHCREGHSGKUNVPUOEOVUY
For this problem, please do the following:
(a) provide an analysis detailing its strength/weakness;
(b) attempt to uncover the plaintext associated with the ciphertext;
(c) attempt to determine the secret key (a, b) used.
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