原文中的两个“l”分别加密成T和D，而且密文中的同样的字符也可能代表不同的原文，比如密文中的L，分别代表了原文中的“e”和“d”。
解密方法
解密公式：P = (C - K)%26
C：密文
P：原文
K：第几套加密方式
如果P<0,P+26取得正序
代码实现
1 import java.util.ArrayList; 2 import java.util.Arrays; 3 import java.util.List; 4 import java.util.Optional; 5 /** 6 * 维吉尼亚加密解密 7 * @author 逆熵 8 * 9 */ 10 public class VirginiaPassword { 11 12 //Virginia Password table 13 private static final String VIRGINIA_PASSWORD_TABLE_ARRAY[] = {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"}; 14 public static final List<String> VIRGINIA_PASSWORD_TABLE_ARRAY_LIST = Arrays.asList(VIRGINIA_PASSWORD_TABLE_ARRAY); 15 16 /** 17 * 18 * 判断对象是否为空，为空返回false，非空返回true 19 * @param object 20 * @return 21 */ 22 public static boolean isNotNull(Object object) { 23 return Optional.ofNullable(object).isPresent(); 24 } 25 26 /** 27 * 判断字符串非null，并且不为空字符串 28 * @param str 29 * @return 30 */ 31 public static boolean isStringNotEmpty(String str) { 32 return isNotNull(str)&&str.trim()!=""; 33 } 34 35 /** 36 * C = P + K (mod 26). 37 * 维吉尼亚加密 38 * @param original 原文 39 * @param secretKey 密钥 40 * @return 41 */ 42 public static String virginiaEncode(String original,String secretKey) { 43 if(isStringNotEmpty(secretKey)&&isStringNotEmpty(original)){ 44 char[] secretCharArray = secretKey.toCharArray(); 45 char[] originalCharArray = original.toCharArray(); 46 int length = originalCharArray.length; 47 48 List<Integer> list = getSecretKeyList(secretCharArray, length); 49 50 StringBuffer sb = new StringBuffer(); 51 for(int m=0;m<length;m++) { 52 char ch = originalCharArray[m]; 53 int charIndex = VIRGINIA_PASSWORD_TABLE_ARRAY_LIST.indexOf(String.valueOf(ch).toUpperCase()); 54 if(charIndex==-1) { 55 sb.append(String.valueOf(ch)); 56 continue; 57 } 58 59 int size = VIRGINIA_PASSWORD_TABLE_ARRAY_LIST.size(); 60 //C = P + K (mod 26). 获取偏移量索引 61 int tmpIndex = (charIndex + list.get(m))%size; 62 sb.append(VIRGINIA_PASSWORD_TABLE_ARRAY_LIST.get(tmpIndex)); 63 64 } 65 return sb.toString(); 66 } 67 return null; 68 } 69 70 /** 71 * P = C - K (mod 26). 72 * 维吉尼亚解密 73 * @param cipherText 密文 74 * @param secretKey 密钥 75 * @return 76 */ 77 public static String virginiaDecode(String cipherText,String secretKey) { 78 if(isStringNotEmpty(cipherText)&&isStringNotEmpty(secretKey)) { 79 char[] secretCharArray = secretKey.toCharArray(); 80 char[] cipherCharArray = cipherText.toCharArray(); 81 int length = cipherCharArray.length; 82 83 List<Integer> list = getSecretKeyList(secretCharArray, length); 84 StringBuffer sb = new StringBuffer(); 85 for(int m=0;m<length;m++) { 86 char ch = cipherCharArray[m]; 87 int charIndex = VIRGINIA_PASSWORD_TABLE_ARRAY_LIST.indexOf(String.valueOf(ch).toUpperCase()); 88 if(charIndex==-1) { 89 sb.append(String.valueOf(ch)); 90 continue; 91 } 92 93 int size = VIRGINIA_PASSWORD_TABLE_ARRAY_LIST.size(); 94 //P = C - K (mod 26). 模逆运算求索引 95 int len = (charIndex - list.get(m))%size; 96 //索引小于零，加模得正索引 97 int tmpIndex = len<0?len+size:len; 98 sb.append(VIRGINIA_PASSWORD_TABLE_ARRAY_LIST.get(tmpIndex)); 99 100 } 101 102 return sb.toString(); 103 } 104 105 return null; 106 } 107 108 /** 109 * 获取密钥集合 110 * @param secretCharArray 密钥字符数组 111 * @param length 原文或密文的长度 112 * @return 113 */ 114 private static List<Integer> getSecretKeyList(char[] secretCharArray, int length) { 115 List<Integer> list = new ArrayList<Integer>(); 116 for (char c : secretCharArray) { 117 int index = VIRGINIA_PASSWORD_TABLE_ARRAY_LIST.indexOf(String.valueOf(c).toUpperCase()); 118 list.add(index); 119 } 120 121 122 if(list.size()>length) { 123 //截取和目标原文或密文相同长度的集合 124 list = list.subList(0, length); 125 }else { 126 Integer[] keyArray = list.toArray(new Integer[list.size()]); 127 int keySize = list.size(); 128 //整除 129 int count = length/keySize; 130 for(int i=2;i<=count;i++) { 131 for (Integer integer : keyArray) { 132 list.add(integer); 133 } 134 } 135 //求余 136 int mold = length%keySize; 137 if(mold>0) { 138 for(int j=0;j<mold;j++) { 139 list.add(keyArray[j]); 140 } 141 142 } 143 } 144 145 return list; 146 } 147 }