# HONS 195N: CRYPTOGRAPHY transform medical device the human scale is manipulated Project Steps: 1.TRACK Mind Mapping steps in the…

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HONS 195N: CRYPTOGRAPHYHOMEWORK # 3Problem 1. The following ciphertext was generated using a simple substitution algorithm:53ddc305))6*;4826)4d.)4d);806*;48c8p60))85;;]8*;:d*8c83(88)5*c;46(;88*96*?;8)*d(;485);5*c2:*d(;4956*2(5*-4)8p8*;4069285);)6c8)4dd;1(d9;48081;8:8d1;48c85;4)485c528806*81(d9;48;(88;4(d?34;48)4d;161;:188;d?;Decrypt the message. [Warning: The resulting message is in English but may not make much sense on afirst reading.]Problem 2. A disadvantage of the general substitution cipher is that both sender and receiver must committhe permuted cipher sequence to memory. A common technique for avoiding this is to use a keyword fromwhich the cipher sequence can be generated. For example, using the keyword CIPHER, write out the keywordfollowed by unused letters in normal order and match this against the plaintext letters:
plain:cipher:
a b c d e f g h i j k l m n o p q r s t u v w x y zC I P H E R A B D F G J K L M N O Q S T U V W X Y Z
If it is felt that this process does not produce sufficient mixing, write the remaining letters on successivelines and then generated the sequence by reading down the columns:C I P H E RA B D F G JK L M N O QS T U B W XY ZThis yields the sequence: C A K S Y I B L T Z P D M U H F N V E G O W R J Q X.Such a system is used in the following ciphertext:UZQSOVUOHXMOPVGPOZPEVSGZWSZOPFPESXUDBMETSXAIZitwasdisclosedyesterdaythatseveralinformalbutVUEPHZHMDZSHZOWSFPAPPDTSVPQUZWYMXUZUHSXdirectcontactshavebeenmadewithpoliticalEPYEPOPDZSZUFPOMBZWPFUPZHMDJUDTMOHMQrepresentativesofthevietconginmoscowDetermine the keyword.Date: Due Wednesday, 16 September 2009.12 HONS 195N HW #3Problem 3. One way to solve the key distribution problem is to use a line from a book that both thesender and the receiver possess. Typically, at least in spy novels, the first sentence of a book serves as thekey. Consider the following ciphertext:SIDKHKDM AF HCRKIABIE SHIMC KD LFEAILAIt was produced using the first sentence of The Other Side of Silence (a book about the spy Kim Philby):The snow lay thick on the steps and the snowflakes driven bythe wind looked black in the headlights of the cars.A simple substitution cipher was used.(a) Decrypt the message.(b) How secure is this cryptosystem compared to a more general substitution cipher? To make the keydistribution problem simple, both parties can agree to use the first or last sentence of a book as thekey. To change the key, they simply need to agree on a new book. The use of the first sentencewould be preferable to the use of the last. Why?

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