com.jchanghong.core.codec.Caesar Maven / Gradle / Ivy
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package com.jchanghong.core.codec;
/**
* 凯撒密码实现
* 算法来自：https://github.com/zhaorenjie110/SymmetricEncryptionAndDecryption
*
* @author looly
*/
public class Caesar {
// 26个字母表
public static final String table = "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz";
/**
* 传入明文，加密得到密文
*
* @param message 加密的消息
* @param offset 偏移量
* @return 加密后的内容
*/
public static String encode(String message, int offset) {
final int len = message.length();
final char[] plain = message.toCharArray();
char c;
for (int i = 0; i < len; i++) {
c = message.charAt(i);
if (false == Character.isLetter(c)) {
continue;
}
plain[i] = encodeChar(c, offset);
}
return new String(plain);
}
/**
* 传入明文解密到密文
*
* @param cipherText 密文
* @param offset 偏移量
* @return 解密后的内容
*/
public static String decode(String cipherText, int offset) {
final int len = cipherText.length();
final char[] plain = cipherText.toCharArray();
char c;
for (int i = 0; i < len; i++) {
c = cipherText.charAt(i);
if (false == Character.isLetter(c)) {
continue;
}
plain[i] = decodeChar(c, offset);
}
return new String(plain);
}
// ----------------------------------------------------------------------------------------- Private method start
/**
* 加密轮盘
*
* @param c 被加密字符
* @param offset 偏移量
* @return 加密后的字符
*/
private static char encodeChar(char c, int offset) {
int position = (table.indexOf(c) + offset) % 52;
return table.charAt(position);
}
/**
* 解密轮盘
*
* @param c 字符
* @return 解密后的字符
*/
private static char decodeChar(char c, int offset) {
int position = (table.indexOf(c) - offset) % 52;
if (position < 0) {
position += 52;
}
return table.charAt(position);
}
// ----------------------------------------------------------------------------------------- Private method end
}