Caesar算法的3种实现

1、Ruby实现：caesar.rb
def encode(plaintext, offset)
 ciphertext = plaintext.dup
 for i in 0..(plaintext.length-1)
  if plaintext[i]>=?a && plaintext[i]<=?z
   ciphertext[i] = ?a + ((plaintext[i] - ?a + offset) % 26)
  elsif plaintext[i]>=?A && plaintext[i]<=?Z
   ciphertext[i] = ?A + ((plaintext[i] - ?A + offset) % 26)
  elsif plaintext[i]>=?0 && plaintext[i]<=?9
   ciphertext[i] = ?0 + ((plaintext[i] - ?0 + offset) % 10)
  end
 end
 print "Ciphertext: ", ciphertext
end

def decode(ciphertext, offset)
 plaintext = ciphertext.dup
 for i in 0..(ciphertext.length-1)
  if ciphertext[i]>=?a && ciphertext[i]<=?z
   plaintext[i] = ?a + ((ciphertext[i] - ?a - offset) % 26)
  elsif ciphertext[i]>=?A && ciphertext[i]<=?Z
   plaintext[i] = ?A + ((ciphertext[i] - ?A - offset) % 26)
  elsif ciphertext[i]>=?0 && ciphertext[i]<=?9
   plaintext[i] = ?0 + ((ciphertext[i] - ?0 - offset) % 10)
  end
 end
 print "Plaintext: ", plaintext
end

print "What do you want to do? (e)ncode or (d)ecode a text?[e/d]"
choose = gets
print "Please input offset value: "
offset = gets
offset = offset[0] - ?0
if choose == "e/n" || choose == "E/n"
 print "Please input the plaintext:"
 text = gets
 encode(text,offset)
else
 print "Please input the ciphertext:"
 text = gets
 decode(text,offset)
end
print "Press ENTER to return."
$stdin.gets

---

2、Groovy实现：caesar.groovy
import java.io.*;

def encode(plaintext, offset) {
 ciphertext = "";
 for (i in plaintext)
  switch(i) {
   case 'a'..'z':
    ciphertext += (char)((char)'a' + (((char)i - (char)'a' + offset) % 26));
    break;
   case 'A'..'Z':
    ciphertext += (char)((char)'A' + (((char)i - (char)'A' + offset) % 26));
    break;
   case '0'..'9':
    ciphertext += Integer.valueOf('0') + (((char)i - (char)'0' + offset) % 10);
  }
 println("Ciphertext: " + ciphertext);
}

def decode(ciphertext, offset) {
 plaintext = "";
 for (i in ciphertext)
  switch(i) {
   case 'a'..'z':
    plaintext += (char)((char)'a' + (((char)i - (char)'a' - offset) % 26));
    break;
   case 'A'..'Z':
    plaintext += (char)((char)'A' + (((char)i - (char)'A' - offset) % 26));
    break;
   case '0'..'9':
    plaintext += Integer.valueOf('0') + (((char)i - (char)'0' - offset) % 10);
  }
 println("Plaintext: " + plaintext);
}

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
print "What to you want to do? (E)ncode or Decode?[e/d]";
action = br.readLine();
print "Please input offset value: ";
int offset = Integer.valueOf(br.readLine());
print "Please input the "
if (action=='d' || action=='D') {
  print "ciphertext: ";
  decode(br.readLine(),offset);
} else {
 print "plaintext: ";
 encode(br.readLine(),offset);
}
println "Press ENTER..."
System.in.read();

---

3、Java实现：Caesar.java
import java.io.*;

public class Caesar {
 public static void encode(String PlainText, int Offset) {
  String CipherText = "";
  for (int i = 0; i < PlainText.length(); i++) {
   if (PlainText.charAt(i) >= 'a' && PlainText.charAt(i) <= 'z')
    CipherText += (char)('a' + ((PlainText.charAt(i) - 'a' + Offset) % 26));
   else if (PlainText.charAt(i) >= 'A' && PlainText.charAt(i) <= 'Z')
    CipherText += (char)('A' + ((PlainText.charAt(i) - 'A' + Offset) % 26));
   else if (PlainText.charAt(i) >= '0' && PlainText.charAt(i) <= '9')
    CipherText += (char)('0' + ((PlainText.charAt(i) - '0' + Offset) % 10));
  }
  System.out.println("Ciphertext: " + CipherText);
 }
 
 public static void decode(String CipherText, int Offset) {
  String PlainText = "";
  for (int i = 0; i < CipherText.length(); i++) {
   if (CipherText.charAt(i) >= 'a' && CipherText.charAt(i) <= 'z')
    PlainText += (char)('a' + ((CipherText.charAt(i) - 'a' - Offset) % 26));
   else if (CipherText.charAt(i) >= 'A' && CipherText.charAt(i) <= 'Z')
    PlainText += (char)('A' + ((CipherText.charAt(i) - 'A' - Offset) % 26));
   else if (CipherText.charAt(i) >= '0' && CipherText.charAt(i) <= '9')
    PlainText += (char)('0' + ((CipherText.charAt(i) - '0' - Offset) % 10));
  }
  System.out.println("PlainText: " + PlainText);
 }
 
 public static void main(String[] args) {
  try {
   BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
   System.out.print ("What to you want to do? (E)ncode or Decode?[e/d]");
   String action = br.readLine();
   System.out.print ("Please input offset value: ");
   int offset = Integer.valueOf(br.readLine());
   System.out.print ("Please input the ");
   if (action.equalsIgnoreCase("d")) {
     System.out.print("ciphertext: ");
     decode(br.readLine(),offset);
   } else {
    System.out.print("plaintext: ");
    encode(br.readLine(),offset);
   }
   System.out.println("Press ENTER...");
   System.in.read();
  } catch(IOException ex) {
   System.out.println(ex.getMessage());
  }
 }
}