libotp.h

   1 /** Practical One-time Pad Library
   2  *
   3  * Created:20080514
   4  * By Jeff Connelly
   5  */
   6
   7 #define MARKER_TO               "to:"
   8 #define MARKER_BEGIN            "--EMOTP_BEGIN--"
   9 #define MARKER_END              "--EMOTP_END--"
  10
  11 /** Pad messages to a multiple of this many bytes, to hide the true
  12  * message length. Higher obscures more information but burns more pad.
  13  * For the best security, this should be the length of the longest message
  14  * you'll ever send, then all messages will be the same length and an attacker
  15  * can tell nothing by the length of the message!.
  16  */
  17 #define PADDING_MULTIPLE        16
  18
  19 #define OFFSET_FILE_EXTENSION   ".off"
  20 #define OFFSET_SIZE             11      /* strlen("4294967296") + 1 */
  21 #define PAD_NAME_LENGTH         4
  22 #define MAX_CONFIG_LINE         1024    /* should be enough, >MAX_PATH */
  23
  24 /* One-time pad. */
  25 typedef struct _PAD {
  26     char *local_filename;
  27     char *name;
  28     FILE *fp;
  29     struct _PAD *next;
  30     /* Use read_offset() and write_offset() to access offset. */
  31 } PAD;
  32
  33
  34 /** Packaged up encrypted message, ready for transport. */
  35 typedef struct _MESSAGE {
  36     unsigned long offset;
  37     PAD *pad;
  38     unsigned long length;
  39     char *cipher_text;
  40 } MESSAGE;
  41
  42 void load_config(char *config_filename);
  43 void show_pads();
  44 FILE *open_offset_file(PAD *p, char *mode);
  45 unsigned long read_offset(PAD *p);
  46 void write_offset(PAD *p, unsigned long offset);
  47 void load_pad(char *local_filename, char *pad_name);
  48 void free_pads();
  49 MESSAGE *unpackage(char *input);
  50 void free_message(MESSAGE *);
  51 char *otp_encrypt(char *input, unsigned int length, char *to, unsigned int *out_length);
  52 unsigned int otp_decrypt(char *input, char **out);
  53