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dbrandom.c
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dbrandom.c
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/*
* Dropbear - a SSH2 server
*
* Copyright (c) 2002,2003 Matt Johnston
* All rights reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE. */
#include "includes.h"
#include "buffer.h"
#include "dbutil.h"
#include "bignum.h"
#include "dbrandom.h"
/* this is used to generate unique output from the same hashpool */
static uint32_t counter = 0;
/* the max value for the counter, so it won't integer overflow */
#define MAX_COUNTER 1<<30
static unsigned char hashpool[SHA1_HASH_SIZE] = {0};
static int donerandinit = 0;
#define INIT_SEED_SIZE 32 /* 256 bits */
/* The basic setup is we read some data from /dev/(u)random or prngd and hash it
* into hashpool. To read data, we hash together current hashpool contents,
* and a counter. We feed more data in by hashing the current pool and new
* data into the pool.
*
* It is important to ensure that counter doesn't wrap around before we
* feed in new entropy.
*
*/
/* Pass len=0 to hash an entire file */
static int
process_file(hash_state *hs, const char *filename,
unsigned int len, int prngd)
{
static int already_blocked = 0;
int readfd;
unsigned int readcount;
int ret = DROPBEAR_FAILURE;
#ifdef DROPBEAR_PRNGD_SOCKET
if (prngd)
{
readfd = connect_unix(filename);
}
else
#endif
{
readfd = open(filename, O_RDONLY);
}
if (readfd < 0) {
goto out;
}
readcount = 0;
while (len == 0 || readcount < len)
{
int readlen, wantread;
unsigned char readbuf[4096];
if (!already_blocked && !prngd)
{
int res;
struct timeval timeout;
fd_set read_fds;
timeout.tv_sec = 2;
timeout.tv_usec = 0;
FD_ZERO(&read_fds);
FD_SET(readfd, &read_fds);
res = select(readfd + 1, &read_fds, NULL, NULL, &timeout);
if (res == 0)
{
dropbear_log(LOG_WARNING, "Warning: Reading the randomness source '%s' seems to have blocked.\nYou may need to find a better entropy source.", filename);
already_blocked = 1;
}
}
if (len == 0)
{
wantread = sizeof(readbuf);
}
else
{
wantread = MIN(sizeof(readbuf), len-readcount);
}
#ifdef DROPBEAR_PRNGD_SOCKET
if (prngd)
{
char egdcmd[2];
egdcmd[0] = 0x02; /* blocking read */
egdcmd[1] = (unsigned char)wantread;
if (write(readfd, egdcmd, 2) < 0)
{
dropbear_exit("Can't send command to egd");
}
}
#endif
readlen = read(readfd, readbuf, wantread);
if (readlen <= 0) {
if (readlen < 0 && errno == EINTR) {
continue;
}
if (readlen == 0 && len == 0)
{
/* whole file was read as requested */
break;
}
goto out;
}
sha1_process(hs, readbuf, readlen);
readcount += readlen;
}
ret = DROPBEAR_SUCCESS;
out:
close(readfd);
return ret;
}
void addrandom(char * buf, unsigned int len)
{
hash_state hs;
/* hash in the new seed data */
sha1_init(&hs);
/* existing state (zeroes on startup) */
sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
/* new */
sha1_process(&hs, buf, len);
sha1_done(&hs, hashpool);
}
static void write_urandom()
{
#ifndef DROPBEAR_PRNGD_SOCKET
/* This is opportunistic, don't worry about failure */
unsigned char buf[INIT_SEED_SIZE];
FILE *f = fopen(DROPBEAR_URANDOM_DEV, "w");
if (!f) {
return;
}
genrandom(buf, sizeof(buf));
fwrite(buf, sizeof(buf), 1, f);
fclose(f);
#endif
}
/* Initialise the prng from /dev/urandom or prngd. This function can
* be called multiple times */
void seedrandom() {
hash_state hs;
pid_t pid;
struct timeval tv;
clock_t clockval;
/* hash in the new seed data */
sha1_init(&hs);
/* existing state */
sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
#ifdef DROPBEAR_PRNGD_SOCKET
if (process_file(&hs, DROPBEAR_PRNGD_SOCKET, INIT_SEED_SIZE, 1)
!= DROPBEAR_SUCCESS) {
dropbear_exit("Failure reading random device %s",
DROPBEAR_PRNGD_SOCKET);
}
#else
/* non-blocking random source (probably /dev/urandom) */
if (process_file(&hs, DROPBEAR_URANDOM_DEV, INIT_SEED_SIZE, 0)
!= DROPBEAR_SUCCESS) {
dropbear_exit("Failure reading random device %s",
DROPBEAR_URANDOM_DEV);
}
#endif
/* A few other sources to fall back on.
* Add more here for other platforms */
#ifdef __linux__
/* Seems to be a reasonable source of entropy from timers. Possibly hard
* for even local attackers to reproduce */
process_file(&hs, "/proc/timer_list", 0, 0);
/* Might help on systems with wireless */
process_file(&hs, "/proc/interrupts", 0, 0);
process_file(&hs, "/proc/loadavg", 0, 0);
process_file(&hs, "/proc/sys/kernel/random/entropy_avail", 0, 0);
/* Mostly network visible but useful in some situations.
* Limit size to avoid slowdowns on systems with lots of routes */
process_file(&hs, "/proc/net/netstat", 4096, 0);
process_file(&hs, "/proc/net/dev", 4096, 0);
process_file(&hs, "/proc/net/tcp", 4096, 0);
/* Also includes interface lo */
process_file(&hs, "/proc/net/rt_cache", 4096, 0);
process_file(&hs, "/proc/vmstat", 0, 0);
#endif
pid = getpid();
sha1_process(&hs, (void*)&pid, sizeof(pid));
/* gettimeofday() doesn't completely fill out struct timeval on
OS X (10.8.3), avoid valgrind warnings by clearing it first */
memset(&tv, 0x0, sizeof(tv));
gettimeofday(&tv, NULL);
sha1_process(&hs, (void*)&tv, sizeof(tv));
clockval = clock();
sha1_process(&hs, (void*)&clockval, sizeof(clockval));
/* When a private key is read by the client or server it will
* be added to the hashpool - see runopts.c */
sha1_done(&hs, hashpool);
counter = 0;
donerandinit = 1;
/* Feed it all back into /dev/urandom - this might help if Dropbear
* is running from inetd and gets new state each time */
write_urandom();
}
/* return len bytes of pseudo-random data */
void genrandom(unsigned char* buf, unsigned int len) {
hash_state hs;
unsigned char hash[SHA1_HASH_SIZE];
unsigned int copylen;
if (!donerandinit) {
dropbear_exit("seedrandom not done");
}
while (len > 0) {
sha1_init(&hs);
sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
sha1_process(&hs, (void*)&counter, sizeof(counter));
sha1_done(&hs, hash);
counter++;
if (counter > MAX_COUNTER) {
seedrandom();
}
copylen = MIN(len, SHA1_HASH_SIZE);
memcpy(buf, hash, copylen);
len -= copylen;
buf += copylen;
}
m_burn(hash, sizeof(hash));
}
/* Generates a random mp_int.
* max is a *mp_int specifying an upper bound.
* rand must be an initialised *mp_int for the result.
* the result rand satisfies: 0 < rand < max
* */
void gen_random_mpint(mp_int *max, mp_int *rand) {
unsigned char *randbuf = NULL;
unsigned int len = 0;
const unsigned char masks[] = {0xff, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f};
const int size_bits = mp_count_bits(max);
len = size_bits / 8;
if ((size_bits % 8) != 0) {
len += 1;
}
randbuf = (unsigned char*)m_malloc(len);
do {
genrandom(randbuf, len);
/* Mask out the unrequired bits - mp_read_unsigned_bin expects
* MSB first.*/
randbuf[0] &= masks[size_bits % 8];
bytes_to_mp(rand, randbuf, len);
/* keep regenerating until we get one satisfying
* 0 < rand < max */
} while (mp_cmp(rand, max) != MP_LT);
m_burn(randbuf, len);
m_free(randbuf);
}