这段代码我已经写完了，现在要求我使用频率分析来破解我不太清楚的代码。
据我了解，我必须先计算字符串中字母的频率，然后我会说将其与德语中出现频率最高的字母进行比较，然后用冒泡排序对其进行排序。它是否正确？
如果有人能给我想法或提示从哪里开始，我将不胜感激。提前谢谢你。
已编辑:大家好，我刚刚编辑了我的代码，频率分析现在似乎工作正常。如果你们可以对我的代码发表评论或批评，这将对我有所帮助。谢谢! 顺便说一句，它是德语，我改变了它。
#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <ctype.h>
#define MAX 100
struct Data
{
char letter;
int num;
};
typedef struct Data DATA;
void encode(char message[], int shift)
{
int i;
FILE *pout;
pout = fopen("Output_encode.txt", "w");
if (pout == NULL)
{
printf("File could not be opened for writing!\n");
exit(1);
}
for(i=0;i<strlen(message);i++)
{
if (!isalpha(message[i]))
continue;
// checking for upper case
if(isupper(message[i]))
message[i]=((message[i]-'A') + shift) % 26 + 'A';
else
//checking for lower case
if(islower(message[i]))
message[i]=((message[i]-'a') + shift) % 26 + 'a';
}
printf("\n\tEncoded text: %s\n", message);
fprintf(pout, "%s\n", message);
if (fclose(pout) != 0)
printf("Error in closing file!\n");
}
void decode(char message[], int shift)
{
int i;
FILE *pout;
pout = fopen("Output_decode.txt", "w");
if (pout == NULL)
{
printf("File could not be opened for writing!\n");
exit(1);
}
for(i=0;i<strlen(message);i++)
{
if (!isalpha(message[i]))
continue;
// checking for upper case
if(isupper(message[i]))
message[i]=((message[i]-'A') + (26-shift)) % 26 + 'A';
else
//checking for lower case
if(islower(message[i]))
message[i]=((message[i]-'a') + (26-shift)) % 26 + 'a';
}
printf("\n\tDecoded text: %s\n", message);
fprintf(pout, "%s\n", message);
if (fclose(pout) != 0)
printf("Error in closing file!\n");
}
void textfile_decode()
{
FILE *pin, *pout;
char filename_in[MAX], filename_out[MAX];
char text[MAX];
char text3[MAX]={0};
char table[26] = {'e','n','i','r','s','t','a','d','h','u','l','c','g','o','m','b','f','w','k','z','p','v','j','y','x','q'}; //Frequency letters in German dictionary
DATA temptext, text2[26];
int temp, position;
int i, m, max, trial, l=0, n=0, k=0;
printf("Enter name of input file: ");
scanf("%s", filename_in);
pin = fopen(filename_in, "r");
if (pin == NULL)
{
printf("File could not be opened for reading!");
}
printf("Enter name of output file: ");
scanf("%s", filename_out);
pout = fopen(filename_out, "w");
if (pout == NULL)
{
printf("File could not be opened for writing!");
}
printf("\nOriginal Code:\n");
while(!feof(pin))
{
fgets(text, MAX, pin); //Read from textfile
fputs(text, stdout); //Show original code on console
}
printf("\n");
if (pin == NULL)
{
printf("File could not be opened for reading!");
}
fclose(pin);
pin = fopen(filename_in, "r");
for (i = 0; i <= 25; i++)
{
text2[i].letter = 'a' + i; //Array elements A-Z
text2[i].num = 0; //Number of letters (Frequency)
}
while(!feof(pin))
{
i = 0;
fgets(text, MAX, pin); //Read from textfile per line
while(text[i] != '\0')
{
if(1 == isupper(text[i])) // Replace capital letters with small
{
text[i] += 32;
}
switch(text[i]) //Counting letters (letter frequency)
{
case 'a':
text2[0].num += 1;
break;
case 'b':
text2[1].num += 1;
break;
case 'c':
text2[2].num += 1;
break;
case 'd':
text2[3].num += 1;
break;
case 'e':
text2[4].num += 1;
break;
case 'f':
text2[5].num += 1;
break;
case 'g':
text2[6].num += 1;
break;
case 'h':
text2[7].num += 1;
break;
case 'i':
text2[8].num += 1;
break;
case 'j':
text2[9].num += 1;
break;
case 'k':
text2[10].num += 1;
break;
case 'l':
text2[11].num += 1;
break;
case 'm':
text2[12].num += 1;
break;
case 'n':
text2[13] .num+= 1;
break;
case 'o':
text2[14].num += 1;
break;
case 'p':
text2[15].num += 1;
break;
case 'q':
text2[16].num += 1;
break;
case 'r':
text2[17].num += 1;
break;
case 's':
text2[18].num += 1;
break;
case 't':
text2[19].num += 1;
break;
case 'u':
text2[20].num += 1;
break;
case 'v':
text2[21].num += 1;
break;
case 'w':
text2[22].num += 1;
break;
case 'x':
text2[23].num += 1;
break;
case 'y':
text2[24].num += 1;
break;
case 'z':
text2[25].num += 1;
break;
default: break;
}
i++;
}
}
for(i = 0; i <= 26; i++) // Sorting array text2 according to letter frequency
{
temp = text2[i].num;
for(m = i+1; m <= 27; m++)
{
if(text2[m].num > temp)
{
max = m;
temp = text2[m].num;
}
}
temptext = text2[max];
text2[max] = text2[i];
text2[i] = temptext;
}
fclose(pin);
fclose(pout);
pin = fopen(filename_in, "r");
pout = fopen(filename_out, "w");
do
{
k += 1;
} while (text2[k].num == text2[k+1].num); //Check--> How many letters have the same frequency
trial = 2;
while(!feof(pin))
{
fgets(text, MAX, pin);
do
{
position = table[l] - text2[n].letter; // determine letter position
i = 0;
do
{
if(0 !=isalpha(text[i]))
{
if(0 != isupper(text[i])) // Checking for uppercase
{
text3[i] = text[i];
text3[i] = text3[i] + position;
if(text3[i] > 90) // If exceeds Alphabets, start again from 'A'
{
text3[i] = text3[i] - 26;
}
else if (text3[i] < 65)
{
text3[i] += 26;
}
}
else if (0 != islower(text[i])) // checking for lowercase
{
text3[i] = text[i];
text3[i] = text3[i] + position;
if(text3[i] > 122) // If exceeds Alphabets, start again from 'a'
{
text3[i] = text3[i] - 26;
}
else if(text3[i] < 97)
{
text3[i] += 26;
}
}
}
else
{
text3[i] = text[i]; // All other non letters are simply replaced
}
i++;
}while(text[i] != '\0' );
if (trial== 2)
{
printf("\n");
fputs(text3, stdout);
printf("\nCode decrypted? (0)NO (1)YES : ");
scanf("%d", &trial);
printf("\n");
}
if (trial == 0 && n != k) // Code not decrypted, letters have different frequency
{
n++;
trial = 2;
}
if (trial == 0 && n == k) // Code not decrypted, letters have same frequency
{
l++;
n = 0;
trial = 2;
}
if (trial == 3) // First line of code is decrypted, following lines will decrypted using same shift position
{
trial = 1;
}
}while(trial != 1);
fputs(text3, stdout); //Show on console window
fputs(text3, pout);
memset(text3,'\0',100); // Reset text3 array
memset(text,'\0',100); // Reset text array
trial = 3; // First line of code decrypted, shift position is saved
}
fclose(pin);
fclose(pout);
}
int main()
{
int shift, choice1, choice2;
char message[MAX];
do{
printf("Selection: \n");
printf("(1) Encode/Decode\n");
printf("(2) Decode Textfile\n");
printf("(3) End Programme\n");
printf("User input: ");
scanf("%d", &choice1);
fflush(stdin);
switch(choice1){
case 1:
printf("\nEnter message to be encrypted: ");
gets(message);
printf("Enter shift amount (1-25): ");
scanf("%d", &shift);
printf("\nSelection: \n");
printf("(1) Encode\n");
printf("(2) Decode\n");
printf("User input: ");
scanf("%d", &choice2);
switch(choice2)
{
case 1:
encode(message, shift);
break;
case 2:
decode(message, shift);
break;
}
break;
case 2:
textfile_decode();
break;
}
printf("\n\n");
}while(choice1!=3);
printf("\n");
return 0;
}
最佳答案
A Caesar ciphre通过移动 n 个位置来更改字符。
解决移位密码有两种非常简单的方法:
打印出所有 25 种可能的解决方案。手动选择包含可读文本的文本。
获取字符(不是单词)的出现频率。然后执行与消息所用语言的频率表最匹配的转换(你的情况是英语？)。
关于c - 频率分析？凯撒密码C，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19764689/