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caesar java_java实现caesar加解密算法

百里骏
2023-12-01

凯撒大帝不仅战功卓越,同时对密码算法也是很有研究啊。下面要介绍的加密算法就是由其本人研究并在战争中使用,包括对后人也有着深远的影响。好了,不扯淡了,下面步入正题。

凯撒加密(Caesar cipher)是一种简单的消息编码方式:它根据字母表将消息中的每个字母移动常量位k。举个例子如果k等于3,则在编码后的消息中,每个字母都会向后移动3位:a会被替换为d;b会被替换成e;依此类推。字母表末尾将回卷到字母表开头。于是,w会被替换为z,x会被替换为a。

下面是JAVA的实现代码,包括对数字和字母表的两种实现方式。

ICaesar.java

public interface ICaesar {

String encrypt(String text, int shiftNum);

String decrypt(String text, int shiftNum);

}

Caesar.java

public abstract class Caesar implements ICaesar {

private String table = "";

public Caesar(String table) {

this.table = table;

}

protected void setTable(String table) {

this.table = table;

}

protected String encryptText(String text, int shiftNum) {

int len = table.length();

StringBuffer result = new StringBuffer();

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

char curChar = text.charAt(i);

int idx = table.indexOf(curChar);

if (idx == -1) {

result.append(curChar);

continue;

}

idx = ((idx + shiftNum) % len);

result.append(table.charAt(idx));

}

return result.toString();

}

@Override

public String encrypt(String text, int shiftNum) {

// TODO Auto-generated method stub

return encryptText(text, shiftNum);

}

@Override

public String decrypt(String text, int shiftNum) {

// TODO Auto-generated method stub

shiftNum = table.length() + (shiftNum % table.length());

return encryptText(text, shiftNum);

}

}

LetterCaesar.java

public class LetterCaesar extends Caesar {

private final static String upperLetter = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

private final static String lowerLetter = "abcdefghijklmnopqrstuvwxyz";

public LetterCaesar() {

super(upperLetter);

// TODO Auto-generated constructor stub

}

private void checkTextTypeAndSetTable(String text) {

char cur = text.charAt(0);

if (Character.isUpperCase(cur)) {

setTable(upperLetter);

} else {

setTable(lowerLetter);

}

}

@Override

public String encrypt(String text, int shiftNum) {

// TODO Auto-generated method stub

checkTextTypeAndSetTable(text);

return super.encrypt(text, shiftNum);

}

@Override

public String decrypt(String text, int shiftNum) {

// TODO Auto-generated method stub

checkTextTypeAndSetTable(text);

return super.decrypt(text, shiftNum);

}

/**

* @param args

*/

public static void main(String[] args) {

ICaesar numberCaesar = new LetterCaesar();

String encodeStr = numberCaesar

.encrypt("ABCDEFGHIGJLMNOPQRSTUVWXYZ", 3);

System.out.println(encodeStr);

String decodeStr = numberCaesar.decrypt(encodeStr, -3);

System.out.println(decodeStr);

encodeStr = numberCaesar.encrypt("abcdefghijklmnopqrstuvwxyq", 3);

System.out.println(encodeStr);

decodeStr = numberCaesar.decrypt(encodeStr, -3);

System.out.println(decodeStr);

}

}

NumberCaesar.java

public class NumberCaesar extends Caesar {

public NumberCaesar() {

super("0123456789");

// TODO Auto-generated constructor stub

}

/**

* @param args

*/

public static void main(String[] args) {

ICaesar numberCaesar = new NumberCaesar();

String encodeStr = numberCaesar.encrypt("0123456789", 13);

System.out.println(encodeStr);

String decodeStr = numberCaesar.decrypt(encodeStr, -13);

System.out.println(decodeStr);

}

}

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