Another method used in a ciphertext attack (see previous problem) is called the statistical approach, in which the intruder intercepts a long ciphertext and tries to analyze the statistics of the characters in the ciphertext. A simple cipher like the additive cipher does not change the statistics of the characters because encryption is one-to-one. Assume the intruder has intercepted the following ciphertext and the most common character in an English plaintext is the character “e”. Use this knowledge to find the key of the cipher and decrypt the ciphertext.

XLILSYWIMWRSAJSVWEPIJSVJSYVQMPPMSRHSPPEVWMXMWASVXLQSVILYVVCFIJSVIXLIWIPPIVVIGIMZIWQSVISJJIVW

Previous Problem

One of the attacks an intruder can apply to a simple cipher like an additive cipher is called the ciphertext attack. In this type of attack, the intruder intercepts the cipher and tries to find the key and eventually the plaintext. One of the methods used in a ciphertext attack is called the brute-force approach, in which the intruder tries several keys and decrypts the message until the message makes sense. Assume the intruder has intercepted the ciphertext “UVACLYZLJBYL”. Try to decrypt the message by using keys beginning with 1 and continuing until a plaintext appears that makes sense.