Vigenère密码

Posted 2020-08-02

1197 Vigenère密码

 

2012年NOIP全国联赛提高组

 时间限制: 1 s

 空间限制: 128000 KB

 题目等级 : 黄金 Gold

 

 

题目描述 Description

16 世纪法国外交家Blaise de Vigenère设计了一种多表密码加密算法——Vigenère密码。Vigenère 密码的加密解密算法简单易用，且破译难度比较高，曾在美国南北战争中为南军所广泛使用。

在密码学中，我们称需要加密的信息为明文，用 M 表示；称加密后的信息为密文，用C 表示；而密钥是一种参数，是将明文转换为密文或将密文转换为明文的算法中输入的数据，记为k。 在Vigenère密码中， 密钥k是一个字母串， k=k1k2…kn。当明文M=m1m2…mn时，得到的密文C=c1c2…cn，其中ci=mi®ki，运算®的规则如下表所示：

 

Vigenère加密在操作时需要注意：

 

1.  ®运算忽略参与运算的字母的大小写，并保持字母在明文 M中的大小写形式；

 

2.  当明文M的长度大于密钥k的长度时，将密钥k 重复使用。

 

例如，明文M=Helloworld，密钥k=abc 时，密文C=Hfnlpyosnd。

 

明文	H	e	l	l	o	w	o	r	l	D
密钥	a	b	c	a	b	c	a	b	c	a
密文	H	f	n	l	p	y	o	s	n	d

 

输入描述 Input Description

输入共2行。

第一行为一个字符串，表示密钥k，长度不超过100，其中仅包含大小写字母。第二为一个字符串，表示经加密后的密文，长度不超过1000，其中仅包含大小写字母

输出描述 Output Description

输出共1行，一个字符串，表示输入密钥和密文所对应的明文

样例输入 Sample Input

CompleteVictory

Yvqgpxaimmklongnzfwpvxmniytm

样例输出 Sample Output

Wherethereisawillthereisaway

数据范围及提示 Data Size & Hint

对于 100%的数据，输入的密钥的长度不超过 100，输入的密文的长度不超过 1000，且都仅包含英文字母。

 

 1 #include<iostream>
 2 #include<cstring>
 3 using namespace std;
 4 char k[101],m[1001];
 5 int ki[101],mi[1001],lk,lm,sk,sm,x,y,s;//打表太可爱
 6 int f[26][26]={{97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122},
 7                {98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97},
 8                {99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98},
 9                {100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99},
10                {101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100},
11                {102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101},
12                {103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102},
13                {104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103},
14                {105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104},
15                {106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105},
16                {107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106},
17                {108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107},
18                {109,110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108},
19                {110,111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109},
20                {111,112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110},
21                {112,113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111},
22                {113,114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112},
23                {114,115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113},
24                {115,116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114},
25                {116,117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115},
26                {117,118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116},
27                {118,119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117},
28                {119,120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118},
29                {120,121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119},
30                {121,122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120},
31                {122,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121}};
32 int main()
33 {
34     cin>>k+1>>m+1;
35     lk=strlen(k+1);
36     lm=strlen(m+1);
37     while(sm<lm)
38     {
39         if(sk==lk)
40             sk=0;
41         int o=0,j;
42         x=int(m[++sm]);
43         y=int(k[++sk])-97;
44         if(x<97)
45         {
46             x+=32;
47             o=1;
48         }
49         if(y<0)
50             y+=32;
51         for(j=0; j<=25; j++)
52         {
53             if(f[j][y]==x)
54                 break;
55         }
56         if(o==1)
57             cout<<char(j+97-32);
58         else
59             cout<<char(j+97);
60     }
61     return 0;
62 }