A disadvantage of the general monoalphabetic cipher
A disadvantage of the general monoalphabetic cipher is that both sender and
receiver must commit the permuted cipher sequence to memory.A common technique
for avoiding this is to use a keyword from which the cipher sequence can be
generated. For example, using the keyword CIPHER, write out the keyword
followed by unused letters in normal order and match this against the plaintext
letters:
plain: 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 z
cipher: C 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 successive lines and then generate the sequence by reading down the
columns:
C 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
This 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 example in Section 2.2 (the one that begins “it was disclosed
yesterday”). Determine the keyword.
Answers
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Posted 23 May 2017 01:05 AM
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