Question

"Encode and decode a message using a substitution and transposition cipher."

I'm not exactly sure what a substitution and transposition cipher are exactly, but I "think" it has to do with something like this:

I want to encode then decode the string: "HELLO". I have:

c(H) = (8 + 4)mod26 == 12mod26 == 12

H = 12 == L

c(E) = (5+4)mod26

E = 9 == I

c(L) = (12+4)mod26

L = 16 == P x2

c(O) = (15+4)mod26

O = 19 == S

Cipher = LIPPS (done)

(Not sure if that's even the correct way to do it.)

If it is, help me decode this in such a way that I may understand it too.

Else:

Forgive me for my dumb self and please explain to me how substitution and transposition ciphers work.

_edit:

Using substitution and transposition cipher, encode and decode the string: "HELLO"

Answer 1