Question

In affine block cipher systems if f(m)=Am + t, what is f(m1+m2) ?

(a) f(m1) + f(m2) + t

(b) f(m1) + f(m2) + 2t

(c) f(m1) + t

(d) f(m1) + f(m2)

This question was addressed to me in an interview for job.

The origin of the question is Block Cipher Systems in section Block Ciphers and the Data Encryption Standard of Cryptograph & Network Security

Answer 1

Correct answer is (a) f(m1) + f(m2) + t

The explanation: In general  f(∑(i=1 to n) m_i = ∑(i=1 to n) f(m_i) + tδ_n) where δ_n=0 if n is odd and 1 if n is even.