/*
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;
}
}
// Demonstrate ICipher.
public class ICipherDemo {
public static void Main() {
ICipher ciphRef;
BitCipher bit = new BitCipher(27);
SimpleCipher sc = new SimpleCipher();
string plain;
string coded;
// first, ciphRef refers to the simple cipher
ciphRef = sc;
Console.WriteLine("Using simple cipher.");
plain = "testing";
coded = ciphRef.encode(plain);
Console.WriteLine("Cipher text: " + coded);
plain = ciphRef.decode(coded);
Console.WriteLine("Plain text: " + plain);
// now, let ciphRef refer to the bitwise cipher
ciphRef = bit;
Console.WriteLine("\nUsing bitwise cipher.");
plain = "testing";
coded = ciphRef.encode(plain);
Console.WriteLine("Cipher text: " + coded);
plain = ciphRef.decode(coded);
Console.WriteLine("Plain text: " + plain);
}
}
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