A certain message exchange system only enables the use of the 26 uppercase Roman letters, without...

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A certain message exchange system only enables the use of the 26 uppercase Roman letters, without any spaces, punctuation, or special characters. The letters A through Z take numerical values in range 0 through 25 sequentially. A variant of the One-Time Pad was adopted as security mechanism for that system: instead of the usual exclusive-or, key characters are added to the message characters modulo 26 for encryption, Ci (Mi + Ki) mod 26 (and subtracted modulo 26 for decryption, M; (CK) mod 26), ensuring that the result always corresponds to a letter. However, due to a specification failure the designers ended up using the same key for all messages. Show that an attacker who knows a message M and the corresponding ciphertext C can decrypt any other cryptogram C* to recover the corresponding message M* (all the same length), by applying such an attack when M = "LOTSAMONEY", C = "EWWWLUOAOM", C* "GWPSCMCNCV" and writing down the characters of the recovered M* in the blanks below. M* N = M W = W S H T A A R A certain message exchange system only enables the use of the 26 uppercase Roman letters, without any spaces, punctuation, or special characters. The letters A through Z take numerical values in range 0 through 25 sequentially. A variant of the One-Time Pad was adopted as security mechanism for that system: instead of the usual exclusive-or, key characters are added to the message characters modulo 26 for encryption, Ci (Mi + Ki) mod 26 (and subtracted modulo 26 for decryption, M; (CK) mod 26), ensuring that the result always corresponds to a letter. However, due to a specification failure the designers ended up using the same key for all messages. Show that an attacker who knows a message M and the corresponding ciphertext C can decrypt any other cryptogram C* to recover the corresponding message M* (all the same length), by applying such an attack when M = "LOTSAMONEY", C = "EWWWLUOAOM", C* "GWPSCMCNCV" and writing down the characters of the recovered M* in the blanks below. M* N = M W = W S H T A A R