5.45. Consider the cipher that has three keys, three plaintexts, and four ciphertexts that are combined using the following encryption table (which is similar to Table 5.12 used in Example 5.54 on page 265).

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5.45. Consider the cipher that has three keys, three plaintexts, and four ciphertexts
that are combined using the following encryption table (which is similar to Table 5.12
used in Example 5.54 on page 265).
f(m₁) = f(m₂)
Suppose further that the plaintexts and keys are used with the following probabili-
ties:
=
k₁
k2
k3
2
m1
M2
M3
C2 C4
C1
C1
C3
C2
C3 C1 C2
f(m3) =
=
f(k1) = f(k₂) = f(k3)
(c) Compute f(c2 | m₁) and ƒ(c3 | m₁).
(d) Compute f(k₁ | c3) and ƒ(k2 | C3).
=
13.
(a) Compute f(c₁), f(c2), f(C3), and f(c4).
(b) Compute f(c₁ | m₁), ƒ(c₁ | m2), and ƒ(c₁ | m3). Does this cryptosystem have
perfect secrecy?
Transcribed Image Text:5.45. Consider the cipher that has three keys, three plaintexts, and four ciphertexts that are combined using the following encryption table (which is similar to Table 5.12 used in Example 5.54 on page 265). f(m₁) = f(m₂) Suppose further that the plaintexts and keys are used with the following probabili- ties: = k₁ k2 k3 2 m1 M2 M3 C2 C4 C1 C1 C3 C2 C3 C1 C2 f(m3) = = f(k1) = f(k₂) = f(k3) (c) Compute f(c2 | m₁) and ƒ(c3 | m₁). (d) Compute f(k₁ | c3) and ƒ(k2 | C3). = 13. (a) Compute f(c₁), f(c2), f(C3), and f(c4). (b) Compute f(c₁ | m₁), ƒ(c₁ | m2), and ƒ(c₁ | m3). Does this cryptosystem have perfect secrecy?
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