public class mtoc
{

//輸入明文和密鑰，用輸入的密鑰對(duì)明文進(jìn)行加密
public static void main(String[] args)
{int i;
 char[] c=new char[100];
 char[] k1=new char[100];

//輸入
System.out.print("enter a mingwen string:");
 String m=MyInput.readString();
System.out.print("enter a key string:");
 String k=MyInput.readString();


//構(gòu)造密鑰對(duì)照表                                                                                                     

for(i=0;i<k.length();i++)
{
if(k.charAt(i)>='a'&&k.charAt(i)<='z')
k1[i]=(char)(k.charAt(i)-97);
if(k.charAt(i)>='A'&&k.charAt(i)<='Z')
k1[i]=(char)(k.charAt(i)-65);
}

//加密

for(i=0;i<m.length();i++)
{
if(m.charAt(i)>='a'&&m.charAt(i)<='z')
c[i]=(char)((m.charAt(i)-97+k1[i%k.length()])%26+97);
if(m.charAt(i)>='A'&&m.charAt(i)<='Z')
c[i]=(char)((m.charAt(i)-65+k1[i%k.length()])%26+65);
}

//輸出密文
for(i=0;i<c.length;i++)
System.out.print(c[i]);}


}


解密算法程序：

public class ctom
{

//輸入密文和密鑰，用密鑰對(duì)密文解密
public static void main(String[] args)
{int i;
char[] m=new char[100];
char[] k1=new char[100];

//輸入
System.out.print("enter the miwen string:");
String c=MyInput.readString();
System.out.print("enter the key string:");
String k=MyInput.readString();

//構(gòu)造密鑰對(duì)照表
for(i=0;i<k.length();i++)
{
if(k.charAt(i)>='a'&&k.charAt(i)<='z')
k1[i]=(char)(k.charAt(i)-97);
if(k.charAt(i)>='A'&&k.charAt(i)<='Z')
k1[i]=(char)(k.charAt(i)-65);
}

//解密

for(i=0;i<c.length();i++)
{
if(c.charAt(i)>='a'&&c.charAt(i)<='z')
m[i]=(char)((c.charAt(i)-97-k1[i%k.length()]+26)%26+97);
if(c.charAt(i)>='A'&&c.charAt(i)<='Z')
m[i]=(char)((c.charAt(i)-65-k1[i%k.length()]+26)%26+65);
}

//輸出明文
for(i=0;i<m.length;i++)
System.out.print(m[i]);}


}


需要用到的MyInput.java類：

// MyInput.java: Contain the methods for reading int, double, and
// string values from the keyboard
import java.io.*;

public class MyInput
{
  // Read a string from the keyboard
  public static String readString()
  {
    BufferedReader br
      = new BufferedReader(new InputStreamReader(System.in), 1);

    // Declare and initialize the string
    String string = "";

    // Get the string from the keyboard
    try
    {
      string = br.readLine();
    }
    catch (IOException ex)
    {
      System.out.println(ex);
    }

    // Return the string obtained from the keyboard
    return string;
  }

  // Read an int value from the keyboard
  public static int readInt()
  {
    return Integer.parseInt(readString());
  }

  // Read a double value from the keyboard
  public static double readDouble()
  {
    return Double.parseDouble(readString());
  }

  // Read a byte value from the keyboard
  public static byte readByte()
  {
    return Byte.parseByte(readString());
  }

  // Read a short value from the keyboard
  public static short readShort()
  {
    return Short.parseShort(readString());
  }

  // Read a long value from the keyboard
  public static long readLong()
  {
    return Long.parseLong(readString());
  }

  // Read a float value from the keyboard
  public static float readFloat()
  {
    return Float.parseFloat(readString());
  }
}