Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

What property of a cryptographic function is described below?

B = F(A) A = F(B)

share|improve this question
Self-invertibility. –  Arturo Magidin Mar 8 '11 at 2:26
add comment

2 Answers 2

$F$ is an involution. You don't want this property for a block cipher since the function doesn't look "random". On the other hand, a stream cipher works exactly that way, but then it's a bit misleading to think of it as a function $F$: the function is missing an important parameter, namely time.

share|improve this answer
your answer looks broken –  user7939 Mar 8 '11 at 4:05
That's quite probable; in what way? –  Yuval Filmus Mar 8 '11 at 4:46
add comment

Most mechanical cipher machines use a reciprocal cipher, so the machine doesn't need a separate "encode mode" and "decode mode". A reciprocal cipher is an involution.

share|improve this answer
add comment

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.