1. Compute the relative frequency of all letters A...Z in the ciphertext. You may want to use a tool such as the open-source program CrypTool [50] for this task. However, a paper and pencil approach is also still doable. 2. Decrypt the ciphertext with the help of the relative letter frequency of the English language.

Question

Exercise 1 - Review (Substitution Cipher)

1. The ciphertext below was encrypted using a substitution cipher. Decrypt the ciphertext without knowledge of the key.

ywkdmkmj lbmbr nkwerulwbt orkrumh lmkbjl wl m surywru pwopru-rdnvmbwjk wklbwbnbwjk vjyywbbrd bj jxxruwko mxxjudmlhr mkd ravrhhrkb rdnvmbwjk bj wbl vhwrkbl xujy mvujll ywkdmkmj mkd jbpru krwopljuwko urowjkl. bpr nkwerulwbt pml lmvvmhmnurmbr mkd sjlb-lmvvmhmnurmbr drourr sujoumyl wk mouwvnhbnur, xwlpruwrl, rkowkrruwko, rdnvmbwjk, lnlwkrll mdywkwlbumbwjk mkd mvvjnkbmkvt, kmbnumh lvwrkvrl mkd ymbprymbwvl, mkd ljvwmh lvwrkvrl mkd pnymkwbwrl, oumdnmbr lbndwrl, mkd hmc. m knylru jx cpwvp mur mvvurdwbrd nkdru bpr mvvurdwbwko morkvt jx vpmubrurd vjhhrorl mkd nkwerulwbwrl wk bpr spwhwsswkrl. wb mhlj jxxrul lmlwv rdnvmbwjk sujoumyl bpujnop wbl jnkwju pwop lvpjjh mkd lrkwju pwop lvpjjh drsmubyrkbl. msmub xujy wbl ymkdmbr jx wklbunvbwjk, bpr nkwerulwbt suwdrl wbl rabrklwer rkomoryrkb wk urlrmuvp mkd rabrklwjk bpmb lrkrxwb bpr mvmdrywv vjyynkwbt mkd wbl lruewvrd lrvbjul. xnubpruyjur, yln-olv lsrmuprmdl emuwjnl wkwbwmbwerl wk srmvr mkd drerhjsyrkb ml smub jx wbl ewlwjk jx lrvjywko m kmbwjkmh srmvr nkwerulwbt.

Pointers:

1. Compute the relative frequency of all letters A...Z in the ciphertext. You may want to use a tool such as the open-source program CrypTool [50] for this task. However, a paper and pencil approach is also still doable.

2. Decrypt the ciphertext with the help of the relative letter frequency of the English language.