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The W at the beginning of the plaintext string maps into V in the

ciphertext, the O maps into G, and so on.

The code for AlphabetSubstitutionCipherin J ava is as follows:

/* File: AlphabetSubstitutionCipher.java* /

public class AlphabetSubstitutionCipher extends

ConsoleP rogram{

public void run(){

println(‘Alphabet-Substitution Cipher”);

String key = readL ine(“E nter 2 6 -alphabet key:”);

String plaintext = readL ine(“P lain text:”);

String ciphertext = encrypt(plaintext, key);

println(“Ciphertext:” + ciphertext);

private String encrypt(String str, String key){

String result = “ “;

str = str.toUpperCase();

for(int i = 0; i< str.length(); i+ + ){

char ch = str.charAt(i);

if(character.isL etter(ch)){

ch = key.charAt(ch – ‘A’);

}

result + = ch;

}

return result;

}

}

The program AlphabetSubstitutionCipher.j ava asks the user for a key

that needs to be checked by the program for its validity. If the key is

not valid, the program provides a message to the user saying that the

key is invalid and will allow the user to give it another try. As an

example, the program is able to duplicate the following sample run:

AlphabetSubstitutionCipher

Enter 26-letter key: SHORTK EY

That key is illegal