shadow/libmisc/salt.c

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/*
* salt.c - generate a random salt string for crypt()
*
* Written by Marek Michalkiewicz <marekm@i17linuxb.ists.pwr.wroc.pl>,
* public domain.
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*
* l64a was Written by J.T. Conklin <jtc@netbsd.org>. Public domain.
*/
#include <config.h>
#ident "$Id$"
#include <sys/time.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include "prototypes.h"
#include "defines.h"
#include "getdef.h"
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/* local function prototypes */
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#ifndef HAVE_L64A
char *l64a(long value);
#endif
static void seedRNG (void);
static char *gensalt (unsigned int salt_size);
#ifdef USE_SHA_CRYPT
static unsigned int SHA_salt_size (void);
static const char *SHA_salt_rounds (int *prefered_rounds);
#endif
#ifndef HAVE_L64A
static char *l64a(long value)
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{
static char buf[8];
char *s = buf;
int digit;
int i;
if (value < 0) {
errno = EINVAL;
return(NULL);
}
for (i = 0; value != 0 && i < 6; i++) {
digit = value & 0x3f;
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if (digit < 2)
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*s = digit + '.';
else if (digit < 12)
*s = digit + '0' - 2;
else if (digit < 38)
*s = digit + 'A' - 12;
else
*s = digit + 'a' - 38;
value >>= 6;
s++;
}
*s = '\0';
return(buf);
}
#endif /* !HAVE_L64A */
static void seedRNG (void)
{
struct timeval tv;
static int seeded = 0;
if (0 == seeded) {
gettimeofday(&tv, NULL);
srandom (tv.tv_sec + tv.tv_usec);
seeded = 1;
}
}
/*
* Add the salt prefix.
*/
#define MAGNUM(array,ch) (array)[0]=(array)[2]='$',(array)[1]=(ch),(array)[3]='\0'
#ifdef USE_SHA_CRYPT
/*
* Return the salt size.
* The size of the salt string is between 8 and 16 bytes for the SHA crypt
* methods.
*/
static unsigned int SHA_salt_size (void)
{
double rand_rounds = 9 * random ();
rand_rounds /= RAND_MAX;
return 8 + rand_rounds;
}
/* ! Arguments evaluated twice ! */
#define MAX(x,y) ((x) > (y) ? (x) : (y))
#define MIN(x,y) ((x) < (y) ? (x) : (y))
/* Default number of rounds if not explicitly specified. */
#define ROUNDS_DEFAULT 5000
/* Minimum number of rounds. */
#define ROUNDS_MIN 1000
/* Maximum number of rounds. */
#define ROUNDS_MAX 999999999
/*
* Return a salt prefix specifying the rounds number for the SHA crypt methods.
*/
static const char *SHA_salt_rounds (int *prefered_rounds)
{
static char rounds_prefix[18];
long rounds;
if (NULL == prefered_rounds) {
long min_rounds = getdef_long ("SHA_CRYPT_MIN_ROUNDS", -1);
long max_rounds = getdef_long ("SHA_CRYPT_MAX_ROUNDS", -1);
double rand_rounds;
if (-1 == min_rounds && -1 == max_rounds)
return "";
if (-1 == min_rounds)
min_rounds = max_rounds;
if (-1 == max_rounds)
max_rounds = min_rounds;
if (min_rounds > max_rounds)
max_rounds = min_rounds;
srand (time (NULL));
rand_rounds = (max_rounds-min_rounds+1) * random ();
rand_rounds /= RAND_MAX;
rounds = min_rounds + rand_rounds;
} else if (0 == *prefered_rounds)
return "";
else
rounds = *prefered_rounds;
/* Sanity checks. The libc should also check this, but this
* protects against a rounds_prefix overflow. */
if (rounds < ROUNDS_MIN)
rounds = ROUNDS_MIN;
if (rounds > ROUNDS_MAX)
rounds = ROUNDS_MAX;
snprintf (rounds_prefix, 18, "rounds=%ld$", rounds);
/* Sanity checks. That should not be necessary. */
rounds_prefix[17] = '\0';
if ('$' != rounds_prefix[16])
rounds_prefix[17] = '$';
return rounds_prefix;
}
#endif
/*
* Generate salt of size salt_size.
*/
#define MAX_SALT_SIZE 16
#define MIN_SALT_SIZE 8
static char *gensalt (unsigned int salt_size)
{
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static char salt[32];
salt[0] = '\0';
assert (salt_size >= MIN_SALT_SIZE &&
salt_size <= MAX_SALT_SIZE);
seedRNG ();
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strcat (salt, l64a (random()));
do {
strcat (salt, l64a (random()));
} while (strlen (salt) < salt_size);
salt[salt_size] = '\0';
return salt;
}
/*
* Generate 8 base64 ASCII characters of random salt. If MD5_CRYPT_ENAB
* in /etc/login.defs is "yes", the salt string will be prefixed by "$1$"
* (magic) and pw_encrypt() will execute the MD5-based FreeBSD-compatible
* version of crypt() instead of the standard one.
* Other methods can be set with ENCRYPT_METHOD
*
* The method can be forced with the meth parameter.
* If NULL, the method will be defined according to the MD5_CRYPT_ENAB and
* ENCRYPT_METHOD login.defs variables.
*
* If meth is specified, an additional parameter can be provided.
* * For the SHA256 and SHA512 method, this specifies the number of rounds
* (if not NULL).
*/
char *crypt_make_salt (const char *meth, void *arg)
{
/* Max result size for the SHA methods:
* +3 $5$
* +17 rounds=999999999$
* +16 salt
* +1 \0
*/
static char result[40];
size_t salt_len = 8;
const char *method;
result[0] = '\0';
if (NULL != meth)
method = meth;
else {
if ((method = getdef_str ("ENCRYPT_METHOD")) == NULL)
method = getdef_bool ("MD5_CRYPT_ENAB") ? "MD5" : "DES";
}
if (!strcmp (method, "MD5")) {
MAGNUM(result, '1');
#ifdef USE_SHA_CRYPT
} else if (!strcmp (method, "SHA256")) {
MAGNUM(result, '5');
strcat(result, SHA_salt_rounds((int *)arg));
salt_len = SHA_salt_size();
} else if (!strcmp (method, "SHA512")) {
MAGNUM(result, '6');
strcat(result, SHA_salt_rounds((int *)arg));
salt_len = SHA_salt_size();
#endif
} else if (0 != strcmp (method, "DES")) {
fprintf (stderr,
_("Invalid ENCRYPT_METHOD value: '%s'.\n"
"Defaulting to DES.\n"),
method);
result[0] = '\0';
}
/*
* Concatenate a pseudo random salt.
*/
assert (sizeof (result) > strlen (result) + salt_len);
strncat (result, gensalt (salt_len),
sizeof (result) - strlen (result) - 1);
return result;
}