Question

In affine block cipher systems if f(m)=Am + t, what is f(m1+m2+m3) ?

(a) f(m1) + f(m2) + f(m3) + t

(b) f(m1) + f(m2) + f(m3) +2t

(c) f(m1) + f(m2) + f(m3)

(d) 2(f(m1) + f(m2) + f(m3))

The question was asked in quiz.

My doubt is from Block Cipher Systems in division Block Ciphers and the Data Encryption Standard of Cryptograph & Network Security

Answer 1

Correct answer is (c) f(m1) + f(m2) + f(m3)

For explanation I would say: 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.