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  1. /* PlayFair chiper */
  2.  
  3. #include <ctype.h>
  4. #include <stdio.h>
  5. #include <stdlib.h>
  6. #include <string.h>
  7.  
  8. #define MAXSTR 1000
  9. #define WIDTH 5
  10. #define TABLESIZE 25
  11. #define NLETTER 26
  12. #define ENCRYPTION 1
  13. #define DECRYPTION (WIDTH - ENCRYPTION)
  14.  
  15. char *extract(char *, const char *);
  16. void delX(char *);
  17. char *getpair(char *, const char *);
  18. int lookup(const char *, int);
  19. void makepair(char *, const char *);
  20. void maketable(char *, const char *);
  21. char *playfair(const char *, const char *, int, int);
  22. char *replace(char *, const char *, int);
  23. void replace_all(char *, const char *, int);
  24. int rowcoltochar(const char *, int, int);
  25. void showpair(const char *);
  26. const char *topair(char *, const char *);
  27. void showtable(char *);
  28.  
  29. int main(int argc, char *argv[])
  30. {
  31.     char *out = NULL, *out2 = NULL;
  32.     printf("<< ENCRYPTION >>\n");
  33.     out = playfair("hello, world", "fairplay", ENCRYPTION, 1);
  34.     printf("%s\n", out);
  35.     printf("\n<< DECRYPTION >>\n"); 
  36.     out2 = playfair(out, "fairplay", DECRYPTION, 1); 
  37.     printf("%s\n", out2); 
  38.     free(out);
  39.     free(out2);
  40.     return 0;
  41. }
  42.  
  43. char *playfair(const char *src, const char *key, int direction, int verbose)
  44. {
  45.     char table[TABLESIZE];
  46.     char *es = (char *) malloc(strlen(src) + 1);
  47.     char *ek = (char *) malloc(strlen(src) + 1);
  48.     char *out = NULL;
  49.  
  50.     if (direction != ENCRYPTION && direction != DECRYPTION)
  51.         goto error;
  52.     if (es == NULL || ek == NULL)
  53.         goto error;
  54.  
  55.     ek = extract(ek, key);
  56.     if (verbose)
  57.         printf("key:\n%s\n%s\n", key, ek);
  58.     maketable(table, key);
  59.     if (verbose)
  60.         showtable(table);
  61.     es = extract(es, src);
  62.     if (verbose)
  63.             printf("src:\n%s\n%s\n", src, es);
  64.     out = (char *) malloc(strlen(es) * 2 + 1);
  65.     if (out == NULL)
  66.             goto error;
  67.     if (direction == ENCRYPTION) {
  68.         makepair(out, es);
  69.     } else {
  70.         strcpy(out, es);
  71.     }
  72.     if (verbose)
  73.         showpair(out);
  74.     replace_all(out, table, direction);
  75.     if (verbose) {
  76.         showpair(out);
  77.         fflush(stdout);
  78.     }
  79.     if (direction == DECRYPTION)
  80.         delX(out);
  81.     return out;
  82.  
  83. error:
  84.     free(ek);
  85.     free(es);
  86.     free(out);
  87.     return NULL;
  88. }
  89.  
  90. void maketable(char *table, const char *key)
  91. {
  92.     int i, j;
  93.     char used[NLETTER];
  94.     static char k[MAXSTR];
  95.  
  96.     memset(table, '\0', TABLESIZE);
  97.     memset(used, 0, sizeof(used));
  98.     used['J' - 'A'] = 1;
  99.     extract(k, key);
  100.     for (i = 0, j = 0; k[i]; i++) {
  101.         int c = (k[i] == 'J') ? 'I' : k[i];
  102.         if (used[c - 'A'])
  103.             continue;
  104.         used[c - 'A'] = 1;
  105.         table[j++] = c;
  106.     }
  107.     for (i = 0; j < TABLESIZE; j++) {
  108.         while (used[i])
  109.             i++;
  110.         table[j] = i++ + 'A';
  111.     }
  112. }
  113.  
  114. void showtable(char *table)
  115. {
  116.     int i;
  117.     for (i = 0; i < TABLESIZE; i++) {
  118.         int c = table[i];
  119.         if (c == '\0')
  120.             c = '.';
  121.         printf((i % WIDTH) ? " %c" : "%c", c);
  122.         if ((i + 1) % WIDTH == 0)
  123.             printf("\n");
  124.     }
  125. }
  126.  
  127. char *extract(char *to, const char *from)
  128. {
  129.     char *retval = to;
  130.     for (; *from; from++) 
  131.         if (isalpha(*from))
  132.             *to++ = toupper(*from);
  133.     *to = '\0';
  134.     return retval;
  135. }
  136.  
  137. void makepair(char *out, const char *p)
  138. {
  139.     while (p = topair(out, p))
  140.         out += 2;
  141.     out = '\0';
  142. }
  143.  
  144. const char *topair(char *pair, const char *s)
  145. {
  146.     if (*s == '\0')
  147.         return NULL;
  148.     pair[0] = *s++;
  149.     if (pair[0] == *s || *s == '\0')
  150.         pair[1] = 'X';
  151.     else
  152.         pair[1] = *s++;
  153.  
  154.     return s;
  155. }
  156.  
  157. void showpair(const char *s)
  158. {
  159.     int isfirst = 1;
  160.     while (*s) {
  161.         if (!isfirst)
  162.             printf("-");
  163.         isfirst = 0;
  164.         if (s[1] == '\0') {
  165.             /* ありえないと思うが */
  166.             printf("%c", s[0]);
  167.             s++;
  168.         } else {
  169.             printf("%c%c", s[0], s[1]);
  170.             s += 2;
  171.         }
  172.     }
  173.     printf("\n");
  174. }
  175.  
  176. void replace_all(char *s, const char *table, int dec)
  177. {
  178.     while (s[0] && s[1]) {
  179.         replace(s, table, dec);
  180.         s += 2;
  181.     }
  182. }
  183.  
  184. char *replace(char *pair, const char *table, int dec)
  185. {
  186.     int i, pos[2], row[2], col[2];
  187.     for (i = 0; i < 2; i++) {
  188.         pos[i] = lookup(table, pair[i]);
  189.         row[i] = pos[i] / WIDTH;
  190.         col[i] = pos[i] % WIDTH;
  191.     }
  192.     if (row[0] ==  row[1]) {
  193.         for (i = 0; i < 2; i++)
  194.             col[i] = (col[i] + dec) % WIDTH;
  195.     } else if (col[0] == col[1]) {
  196.         for (i = 0; i < 2; i++)
  197.             row[i] = (row[i] + dec) % WIDTH;
  198.     } else {
  199.         int tmp = col[0];
  200.         col[0] = col[1];
  201.         col[1] = tmp;
  202.     }
  203.     for (i = 0; i < 2; i++)
  204.         pair[i] = rowcoltochar(table, row[i], col[i]);
  205.     return pair;
  206. }
  207.  
  208. int lookup(const char *table, int c)
  209. {
  210.     char *p = strchr(table, c);
  211.     return p - table;
  212. }
  213.  
  214. int rowcoltochar(const char *table, int row, int col)
  215. {
  216.     return table[row * WIDTH + col];
  217. }
  218.  
  219. void delX(char *s)
  220. {
  221.     char *t = s;
  222.     while (s[0] && s[1]) {
  223.         *t++ = *s++;
  224.         if (*s != 'X')
  225.             *t++ = *s;
  226.         s++;
  227.     }
  228.     *t = '\0';
  229. }
  230.  
  231. /* END OF FILE */
Success #stdin #stdout 0.01s 2860KB
comments (?)
stdin 
Standard input is empty
stdout 
<< ENCRYPTION >>
key:
fairplay
FAIRPLAY
F A I R P
L Y B C D
E G H K M
N O Q S T
U V W X Z
src:
hello, world
HELLOWORLD
HE-LX-LO-WO-RL-DX
KG-CU-YN-VQ-FC-CZ
KGCUYNVQFCCZ

<< DECRYPTION >>
key:
fairplay
FAIRPLAY
F A I R P
L Y B C D
E G H K M
N O Q S T
U V W X Z
src:
KGCUYNVQFCCZ
KGCUYNVQFCCZ
KG-CU-YN-VQ-FC-CZ
HE-LX-LO-WO-RL-DX
HELLOWORLD
https://ideone.com/4007r
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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