Computing

142 ◾ Computing

example, if we prepare 100 substitutes altogether, and if the frequency of

letter β is approximately α

β

% in plaintexts, we might choose one of the α

β

substitutes for letter β in a cryptotext [2, 8]. An example of a homophonic

substitution cipher is shown in Table17.3. In the next example, we use the

homophonic substitution given in Table17.3.

Example 17.2

A plaintext, “Let us meet tonight in the park,” may be encrypted to

51 82 69 08 86 22 44 16 97 49 90 18 70 25 65 75 32 66 17 39 98 95

78 29 04. Note that this is not a unique cryptotext for the plaintext.

TABLE17.3 A Homophonic Substitution Cipher

A : 01 12 33 47 53