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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"
static int donerandinit = 0;
/* 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];
#define INIT_SEED_SIZE 32 /* 256 bits */
static void readrand(unsigned char* buf, unsigned int buflen);
/* 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.
*
*/
static void readrand(unsigned char* buf, unsigned int buflen) {
static int already_blocked = 0;
int readfd;
unsigned int readpos;
int readlen;
#ifdef DROPBEAR_PRNGD_SOCKET
struct sockaddr_un egdsock;
char egdcmd[2];
#endif
#ifdef DROPBEAR_RANDOM_DEV
readfd = open(DROPBEAR_RANDOM_DEV, O_RDONLY);
if (readfd < 0) {
dropbear_exit("Couldn't open random device");
}
#endif
#ifdef DROPBEAR_PRNGD_SOCKET
readfd = connect_unix(DROPBEAR_PRNGD_SOCKET);
if (readfd < 0) {
dropbear_exit("Couldn't open random device");
}
if (buflen > 255)
dropbear_exit("Can't request more than 255 bytes from egd");
egdcmd[0] = 0x02; /* blocking read */
egdcmd[1] = (unsigned char)buflen;
if (write(readfd, egdcmd, 2) < 0)
dropbear_exit("Can't send command to egd");
#endif
/* read the actual random data */
readpos = 0;
do {
if (!already_blocked)
{
int ret;
struct timeval timeout;
fd_set read_fds;
timeout.tv_sec = 2; /* two seconds should be enough */
timeout.tv_usec = 0;
FD_ZERO(&read_fds);
FD_SET(readfd, &read_fds);
ret = select(readfd + 1, &read_fds, NULL, NULL, &timeout);
if (ret == 0)
{
dropbear_log(LOG_INFO, "Warning: Reading the random source seems to have blocked.\nIf you experience problems, you probably need to find a better entropy source.");
already_blocked = 1;
}
}
readlen = read(readfd, &buf[readpos], buflen - readpos);
if (readlen <= 0) {
if (readlen < 0 && errno == EINTR) {
continue;
}
dropbear_exit("Error reading random source");
}
readpos += readlen;
} while (readpos < buflen);
close (readfd);
}
/* initialise the prng from /dev/(u)random or prngd */
void seedrandom() {
unsigned char readbuf[INIT_SEED_SIZE];
hash_state hs;
/* initialise so that things won't warn about
* hashing an undefined buffer */
if (!donerandinit) {
m_burn(hashpool, sizeof(hashpool));
}
/* get the seed data */
readrand(readbuf, sizeof(readbuf));
/* hash in the new seed data */
sha1_init(&hs);
sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
sha1_process(&hs, (void*)readbuf, sizeof(readbuf));
sha1_done(&hs, hashpool);
counter = 0;
donerandinit = 1;
}
/* hash the current random pool with some unique identifiers
* for this process and point-in-time. this is used to separate
* the random pools for fork()ed processes. */
void reseedrandom() {
pid_t pid;
hash_state hs;
struct timeval tv;
if (!donerandinit) {
dropbear_exit("seedrandom not done");
}
pid = getpid();
gettimeofday(&tv, NULL);
sha1_init(&hs);
sha1_process(&hs, (void*)hashpool, sizeof(hashpool));
sha1_process(&hs, (void*)&pid, sizeof(pid));
sha1_process(&hs, (void*)&tv, sizeof(tv));
sha1_done(&hs, hashpool);
}
/* 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);
}
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