generate ambiguous passwords

osiekhan-pwgen.c

// osiekhan-pwgen: generate password from the following set of
// characters: "S5Ii1l|!0O:;,.`'" (excluding double quotes).
//
// Pass positive integer as the first parameter to specify length
// (defaults to 64 characters if unspecified).
//
// Example:
//   > cc -O3 -W -Wall -Wextra -pedantic -std=c11 -o osiekhan-pwgen{,.c}
//   > ./osiekhan-pwgen
//   l||!.O';:;;i,51'S!:S..l;1S'0O`,.I'5'S,!,;SI`!Oil'S:llO;i:5!5lS5l
//

#include <unistd.h>
#include <stdio.h> // fputs()
#include <stdlib.h> // EXIT_SUCCESS
#include <stdint.h> // uint8_t
#include <string.h> // atoi()
#include <err.h> // err()

// alphabet (length must be power of two)
const char A[] = 
  "S5Ii1l|!0O:;,.`'";

// subtract two to exclude trailing null and get mask
#define AM (sizeof(A) - 2)

static void get_random_bytes(uint8_t * const dst, const size_t len) {
  // open /dev/urandom
  FILE *fh = fopen("/dev/urandom", "rb");
  if (!fh) {
    err(EXIT_FAILURE, "fopen()");
  }

  // read bytes
  if (!fread(dst, len, 1, fh)) {
    err(EXIT_FAILURE, "fread()");
  }

  // close handle
  fclose(fh);
}

int main(int argc, char *argv[]) {
  const int len = (argc > 1) ? atoi(argv[1]) : 64;
  if (len < 1) {
    errx(EXIT_FAILURE, "len < 1");
  }

  // alloc source buffer
  uint8_t * const src = malloc(len);
  if (!src) {
    err(EXIT_FAILURE, "src malloc()");
  }

  // alloc destination buffer
  char * const dst = malloc(len + 1);
  if (!dst) {
    err(EXIT_FAILURE, "dst malloc()");
  }

  // fill src buf with random bytes
  get_random_bytes(src, len);

  // fill dst buf
  for (int i = 0; i < len; i++) {
    dst[i] = A[src[i] & AM];
  }
  dst[len] = '\0';

  fputs(dst, stdout);
  fputc('\n', stdout);

  // return success
  return EXIT_SUCCESS;
}