//PLAYFAIR.H 头文件 #ifndef _PLAY_FAIR_H_ #define _PLAY_FAIR_H_ void cst_playfair_table (char *in_key); void prnt_playfair_table (); int playfair_encrypt (char *plain_txt, char *cipher_txt); int playfair_decrypt (char *cipher_txt, char *plain_txt); #endif //PLAYFAIR.C 源文件 #include "playfair.h" #include #include #include char playfair_table[5][5]; void get_x_y (char c, int *x, int *y) { int i, j; for (i = 0; i < 5; ++i) { for (j = 0; j < 5; ++j) { if (playfair_table[i][j] == c) { *x = i; *y = j; return; } } } } char get_char_x_y (int x, int y) { if (x < 0) x += 5; if (y < 0) y += 5; return playfair_table[x % 5][y % 5]; } void cst_playfair_table (char *in_key) { int i = 0, j, k; int char_count = 0, left_ch_index = 0; char ch, left_chs[26] = {0}, key[26] = {0}; int key_len; strcpy (key, in_key); key_len = strlen (key); while (1) { if (key[i] == ' ') { for (j = i; j < key_len - 1; ++j) key[j] = key[j + 1]; key_len--; } if (i == key_len) break; i++; } for (i = 0; i < 26; ++i) { ch = 'a' + i; j = 0; char_count = 0; while (1) { if (key[j] == ch) { char_count++; if (char_count > 1) { for (k = j; k < key_len -1; ++k) key[k] = key[k + 1]; key_len--; } else j++; } else j++; if (j == key_len) break; } if (char_count == 0) left_chs[left_ch_index++] = ch; } for (i = 0; i < left_ch_index; ++i) key[key_len++] = left_chs[i]; for (i = 0; i < 26; ++i) { if (key[i] == 'z') { for (j = i; j < 25; ++j) key[j] = key[j + 1]; } } for (i = 0; i < 5; ++i) { for (j = 0; j < 5; ++j) playfair_table[i][j] = key[5 * i + j]; } } void prnt_playfair_table () { int i, j; printf ("Playfair Table:\n"); for (i = 0; i < 5; ++i) { printf ("\...
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