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/*
C#: The Complete Reference
by Herbert Schildt
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
using System;
// An encryption interface.
public interface ICipher {
string encode(string str);
string decode(string str);
}
/* A simple implementation of ICipher that codes
a message by shifting each character 1 position
higher. Thus, A becomes B, and so on. */
class SimpleCipher : ICipher {
// Return an encoded string given plaintext.
public string encode(string str) {
string ciphertext = "";
for(int i=0; i < str.Length; i++)
ciphertext = ciphertext + (char) (str[i] + 1);
return ciphertext;
}
// Return an decoded string given ciphertext.
public string decode(string str) {
string plaintext = "";
for(int i=0; i < str.Length; i++)
plaintext = plaintext + (char) (str[i] - 1);
return plaintext;
}
}
/* This implementation of ICipher uses bit
manipulations and key. */
class BitCipher : ICipher {
ushort key;
// Specify a key when constructing BitCiphers.
public BitCipher(ushort k) {
key = k;
}
// Return an encoded string given plaintext.
public string encode(string str) {
string ciphertext = "";
for(int i=0; i < str.Length; i++)
ciphertext = ciphertext + (char) (str[i] ^ key);
return ciphertext;
}
// Return an decoded string given ciphertext.
public string decode(string str) {
string plaintext = "";
for(int i=0; i < str.Length; i++)
plaintext = plaintext + (char) (str[i] ^ key);
return plaintext;
}
}
// Use ICipher.
// A class for storing unlisted telephone numbers.
class UnlistedPhone {
string pri_name; // supports name property
string pri_number; // supports number property
ICipher crypt; // reference to encryption object
public UnlistedPhone(string name, string number, ICipher c)
{
crypt = c; // store encryption object
pri_name = crypt.encode(name);
pri_number = crypt.encode(number);
}
public string Name {
get {
return crypt.decode(pri_name);
}
set {
pri_name = crypt.encode(value);
}
}
public string Number {
get {
return crypt.decode(pri_number);
}
set {
pri_number = crypt.encode(value);
}
}
}
// Demonstrate UnlistedPhone
public class UnlistedDemo {
public static void Main() {
UnlistedPhone phone1 =
new UnlistedPhone("Tom", "555-3456", new BitCipher(27));
UnlistedPhone phone2 =
new UnlistedPhone("Mary", "555-8891", new BitCipher(9));
Console.WriteLine("Unlisted number for " +
phone1.Name + " is " +
phone1.Number);
Console.WriteLine("Unlisted number for " +
phone2.Name + " is " +
phone2.Number);
}
}
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