/*
 * TEA Total Copyright (c) Alex Holden <alex@linuxhacker.org> 2000, 2001.
 *
 * This code is public domain; you can do whatever you want with it, though I
 * would prefer you to contribute any bug fixes back to me if possible.
 * This software comes with NO WARRANTY WHATSOEVER, not even the implied
 * warranties of merchantability and fitness for a particular purpose.
 *
 * randint.c: Generates a random key using a hash of key press timings.
 */

#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <termios.h>
#include <sys/time.h>

#include "teatotal.h"
#include "tea-kgen.h"
#include "md5.h"

#define TEA_KGEN_MSG "Please mash the keyboard to generate randomness.\n"

/*
 * For systems which don't have a /dev/random or equivalent, we generate the
 * key data by timing the gap between key presses for 128 presses (I'm assuming
 * that we can safely get one bit of randomness from each key stroke), and then
 * distilling the data by performing an MD5 hash on the resulting array of
 * times. The MD5 hash is performed by the functions in the file md5.c, which
 * is a public domain implementation of MD5 by Colin Plumb. If you find the
 * number of key presses you need to do annoying, it is probably safe to
 * reduce the loop count somewhat (keep it a multiple of 16 though).
 */
void generate_key(teastate *state)
{
	char c;
	int bits;
	long udiff, sdiff;
	u32 diffs[16];
	struct termios ti;
	struct timeval tv, otv;
	struct MD5Context md5state;

	/* Check that this is being run from a terminal */
	if(!isatty(STDIN_FILENO)) die("Must be run from a terminal\n");

	/* Save the current terminal attributes */
	tcgetattr(STDIN_FILENO, &origtermattr);
	/* Register a cleanup function to restore the attributes on exit */
	atexit(restore_termattr);

	/* Clear ICANON and ECHO on STDIN so we get characters one at a time
	 * and they aren't echoed to the console, and flush the input buffer */
	tcgetattr(STDIN_FILENO, &ti);
	ti.c_lflag &= ~(ICANON | ECHO);
	tcsetattr(STDIN_FILENO, TCSAFLUSH, &ti);

	/* Print a message about needing to generate randomness */
	safe_write(STDERR_FILENO, TEA_KGEN_MSG, sizeof(TEA_KGEN_MSG));

	/* Initialise the MD5 state structure */
	MD5Init(&md5state);

	/* Get the initial time */
	gettimeofday(&otv, NULL);

	/* Loop around once per key press for a total of 128 times */
	for(bits = 0; bits < 128; bits++) {
		/* Read the next keypress- the value of the key is ignored */
		if(read(STDIN_FILENO, &c, 1) != 1)
			die("Error reading from keyboard\n");
		/* Get the new time */
		gettimeofday(&tv, NULL);
		/* Calculate the difference between the new and old times */
		udiff = tv.tv_usec - otv.tv_usec;
		sdiff = tv.tv_sec - otv.tv_sec;
		diffs[bits % 16] = (1000000 * sdiff) + udiff;
		/* When the array is full, add the latest delays to the hash */
		if(!((bits + 1) % 16))
			MD5Update(&md5state, (char *)diffs, 64);
		/* Rotate the new time to the old time */
		otv.tv_usec = tv.tv_usec;
		otv.tv_sec = tv.tv_sec;
		/* Give the user an indication that something is happening */
		if(!(bits % 2)) write(STDERR_FILENO, ".", 1);
	}
	/* End the line of dots */
#ifdef DOS_FILE_ENDINGS
	write(STDERR_FILENO, "\r\n", 2);
#else
	write(STDERR_FILENO, "\n", 1);
#endif

	/* Read the random data from the hash structure into the key array */
	MD5Final((unsigned char *)state->k, &md5state);
}