|
DESCRIPTION
The Book cipher is a cipher that utilizes a book to encrypt a
message. The same book is needed to
decrypt the message. The book needs to
be big enough to cover almost all needed words. The process of encrypting and decrypting is simple enough – though time
consuming I imagine. Essentially, you
replace each word with its page,line and word number location in the book. The person decrypting the message needs to know the book and then can
simply look up each word one at a time.
WORK QUESTION 1 Consider
the book called The Great Song Book. It has the page number on the first line of
every page and a separating line of = symbols to demark the beginning/end of
pages. Do the
following work in a file called Book: a)
Write
a function named book_contains_word
that checks to see if a provided word is in the book. It should return true or false. b)
Write
a function named book_contains_text
that checks to see if all words in a provided message is in the book. It should return true or false. c)
Write
a function named location_word that
gets a word and returns a string of form #,#,# where the numbers symbols are
the page number, line number and word number where the word is found. The string “” should be returned if the
word is not in the book. d)
Write
a function named location_text that gets a plaintext message (several words)
and returns the location of every word in the plaintext each on a separate
line (separated by \n). This is
effectively creating a the ciphertext. e)
Write
the function named enc that will get a message as parameter and check if all
words are in the book. If they are, it
returns the ciphertext. If they aren’t,
it returns the word “error”. QUESTION 2 Write the
function dec that will decrypt a book ciphertext. Essentially, it looks up all words based on
the #,#,# addressing scheme used by book ciphers. QUESTION 3 The
following cyphertext has been encrypted using the Book cipher. The book used is The
Great Song Book (same as above).
Decrypt it using your program. 7,13,3 6,9,10 3,4,4 7,3,5 2,9,3 7,13,3 4,15,2 3,30,5 9,27,6 5,25,8 |
