libotp.c

   1 /** Practical One-time Pad Library
   2  *
   3  * Created:20080514
   4  * By Jeff Connelly
   5  */
   6
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <sysexits.h>
  10 #include <string.h>
  11
  12 #define MARKER_TO               "to:"
  13 #define MARKER_BEGIN            "--EMOTP_BEGIN--"
  14 #define MARKER_END              "--EMOTP_END--"
  15
  16 #define OFFSET_FILE_EXTENSION   ".off"
  17 #define OFFSET_SIZE             11      /* strlen("4294967296") + 1 */
  18
  19 /** Packaged up encrypted message, ready for transport. */
  20 typedef struct _PACKAGE {
  21     unsigned long offset;
  22     char *pad_name;
  23     char *cipher_text;
  24 } PACKAGE;
  25
  26 typedef struct _PAD {
  27     char *local_filename;
  28     char *name;
  29     unsigned long offset;
  30     FILE *fp;
  31     struct _PAD *next;
  32 } PAD;
  33
  34 PAD *pads = NULL;
  35
  36 /** Show a list of all loaded pads. */
  37 void show_pads()
  38 {
  39     PAD *p;
  40
  41     for (p = pads; p; p = p->next) {
  42         printf("Pad: %s: %s\n", p->name, p->local_filename);
  43     }
  44 }
  45
  46 /** Open a companion offset file for given pad. Caller must close. */
  47 FILE *open_offset_file(PAD *p)
  48 {
  49     FILE *ofp;
  50     char *offset_filename;
  51     size_t filename_length;
  52
  53     /* Offset is stored in a separate file; pad plus OFFSET_FILE_NAME_EXTENSION. */
  54     filename_length = strlen(p->local_filename) + strlen(OFFSET_FILE_EXTENSION) + 1;
  55     offset_filename = malloc(filename_length);
  56     if (!offset_filename) {
  57         perror("malloc");
  58         exit(EX_UNAVAILABLE);
  59     }
  60     snprintf(offset_filename, filename_length, "%s" OFFSET_FILE_EXTENSION, p->local_filename);
  61
  62     /* Read offset from file. */
  63     ofp = fopen(offset_filename, "rt");
  64     if (!ofp) {
  65         fprintf(stderr, "opening offset file %s failed\n", offset_filename);
  66         perror("fopen");
  67         free(offset_filename);
  68         exit(EX_IOERR);
  69     }
  70     free(offset_filename);
  71
  72     return ofp;
  73 }
  74
  75 /** Read the pad offset of a given pad. */
  76 unsigned long read_offset(PAD *p)
  77 {
  78     FILE *ofp;
  79     char buffer[OFFSET_SIZE];
  80     unsigned long offset;
  81
  82     ofp = open_offset_file(p);
  83
  84     memset(buffer, 0, OFFSET_SIZE);
  85     if (fread(buffer, 1, OFFSET_SIZE - 1, ofp) < 1) {
  86         fprintf(stderr, "could not read offset file for %s\n", p->local_filename);
  87         exit(EX_IOERR);
  88     }
  89
  90     fclose(ofp);
  91
  92     /* We finally got it! */
  93     offset = atol(buffer);
  94
  95     return offset;
  96 }
  97
  98 void write_offset(unsigned long offset)
  99 {
 100 }
 101
 102 /** Load a pad file from disk, adding to 'pads' global. */
 103 void load_pad(char *local_filename)
 104 {
 105     FILE *fp;
 106     PAD *new_pad;
 107
 108     fp = fopen("/Volumes/Not Backed Up/otp/otp-dazzlement", "rb");
 109     if (!fp) {
 110         perror("fopen");
 111         exit(EXIT_FAILURE);
 112     }
 113
 114     new_pad = malloc(sizeof(PAD));
 115     if (!new_pad) {
 116         perror("malloc");
 117         exit(EX_UNAVAILABLE);
 118     }
 119
 120     new_pad->local_filename = strdup(local_filename);
 121     new_pad->name = strdup("dc"); /* TODO */
 122     new_pad->offset = -1; /* TODO */
 123     new_pad->fp = fp;
 124     new_pad->next = NULL;
 125
 126     /* Add to linked list. */
 127     if (!pads) {
 128         pads = new_pad;
 129     } else {
 130         PAD *p, *tail;
 131
 132         /* Find tail */
 133         for (p = pads; p; p = p->next)
 134             tail = p;
 135         tail->next = new_pad;
 136     }
 137 }
 138
 139 /** Close all pads and free allocated memory. */
 140 void free_pads()
 141 {
 142     PAD *p, *next;
 143
 144     for (p = pads; p; p = next) {
 145         free(p->name);
 146         free(p->local_filename);
 147         fclose(p->fp);
 148         next = p->next;
 149         free(p);
 150     }
 151 }
 152
 153 int main()
 154 {
 155     load_pad("/Volumes/Not Backed Up/otp/otp-dazzlement");
 156     load_pad("/Volumes/Not Backed Up/otp/otp-dazzlement");
 157     load_pad("/Volumes/Not Backed Up/otp/otp-dazzlement");
 158
 159     printf("offset=%ld\n", read_offset(pads));
 160
 161     show_pads();
 162     free_pads();
 163
 164     return 0;
 165 }
 166