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>,
* it is in the 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 */
static void seedRNG (void);
static /*@observer@*/const char *gensalt (size_t salt_size);
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#if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
static long shadow_random (long min, long max);
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#endif /* USE_SHA_CRYPT || USE_BCRYPT */
#ifdef USE_SHA_CRYPT
static /*@observer@*/const char *SHA_salt_rounds (/*@null@*/int *prefered_rounds);
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#endif /* USE_SHA_CRYPT */
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#ifdef USE_BCRYPT
static /*@observer@*/const char *gensalt_bcrypt (void);
static /*@observer@*/const char *BCRYPT_salt_rounds (/*@null@*/int *prefered_rounds);
#endif /* USE_BCRYPT */
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#ifdef USE_YESCRYPT
static /*@observer@*/const char *gensalt_yescrypt (void);
static /*@observer@*/const char *YESCRYPT_salt_cost (/*@null@*/long *prefered_rounds);
#endif /* USE_YESCRYPT */
#ifndef HAVE_L64A
static /*@observer@*/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;
if (digit < 2) {
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*s = digit + '.';
} else if (digit < 12) {
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*s = digit + '0' - 2;
} else if (digit < 38) {
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*s = digit + 'A' - 12;
} else {
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*s = digit + 'a' - 38;
}
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value >>= 6;
s++;
}
*s = '\0';
return(buf);
}
#endif /* !HAVE_L64A */
static void seedRNG (void)
{
struct timeval tv;
static int seeded = 0;
if (0 == seeded) {
(void) gettimeofday (&tv, NULL);
srandom (tv.tv_sec ^ tv.tv_usec ^ getpid ());
seeded = 1;
}
}
/*
* Add the salt prefix.
*/
#define MAGNUM(array,ch) (array)[0]=(array)[2]='$',(array)[1]=(ch),(array)[3]='\0'
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#ifdef USE_BCRYPT
/*
* Using the Prefix $2a$ to enable an anti-collision safety measure in musl libc.
* Negatively affects a subset of passwords containing the '\xff' character,
* which is not valid UTF-8 (so "unlikely to cause much annoyance").
*/
#define BCRYPTMAGNUM(array) (array)[0]=(array)[3]='$',(array)[1]='2',(array)[2]='a',(array)[4]='\0'
#endif /* USE_BCRYPT */
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#if defined(USE_SHA_CRYPT) || defined(USE_BCRYPT)
/* It is not clear what is the maximum value of random().
* We assume 2^31-1.*/
#define RANDOM_MAX 0x7FFFFFFF
/*
* Return a random number between min and max (both included).
*
* It favors slightly the higher numbers.
*/
static long shadow_random (long min, long max)
{
double drand;
long ret;
seedRNG ();
drand = (double) (max - min + 1) * random () / RANDOM_MAX;
/* On systems were this is not random() range is lower, we favor
* higher numbers of salt. */
ret = (long) (max + 1 - drand);
/* And we catch limits, and use the highest number */
if ((ret < min) || (ret > max)) {
ret = max;
}
return ret;
}
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#endif /* USE_SHA_CRYPT || USE_BCRYPT */
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#ifdef USE_SHA_CRYPT
/* Default number of rounds if not explicitly specified. */
#define ROUNDS_DEFAULT 5000
/* Minimum number of rounds. */
#define ROUNDS_MIN 1000
/* Maximum number of rounds. */
#define ROUNDS_MAX 999999999
/*
* Return a salt prefix specifying the rounds number for the SHA crypt methods.
*/
static /*@observer@*/const char *SHA_salt_rounds (/*@null@*/int *prefered_rounds)
{
static char rounds_prefix[18]; /* Max size: rounds=999999999$ */
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);
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;
}
rounds = shadow_random (min_rounds, max_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;
}
(void) snprintf (rounds_prefix, sizeof rounds_prefix,
"rounds=%ld$", rounds);
return rounds_prefix;
}
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#endif /* USE_SHA_CRYPT */
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#ifdef USE_BCRYPT
/* Default number of rounds if not explicitly specified. */
#define B_ROUNDS_DEFAULT 13
/* Minimum number of rounds. */
#define B_ROUNDS_MIN 4
/* Maximum number of rounds. */
#define B_ROUNDS_MAX 31
/*
* Return a salt prefix specifying the rounds number for the BCRYPT method.
*/
static /*@observer@*/const char *BCRYPT_salt_rounds (/*@null@*/int *prefered_rounds)
{
static char rounds_prefix[4]; /* Max size: 31$ */
long rounds;
if (NULL == prefered_rounds) {
long min_rounds = getdef_long ("BCRYPT_MIN_ROUNDS", -1);
long max_rounds = getdef_long ("BCRYPT_MAX_ROUNDS", -1);
if (((-1 == min_rounds) && (-1 == max_rounds)) || (0 == *prefered_rounds)) {
rounds = B_ROUNDS_DEFAULT;
}
else {
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;
}
rounds = shadow_random (min_rounds, max_rounds);
}
} else {
rounds = *prefered_rounds;
}
/*
* Sanity checks.
* Use 19 as an upper bound for now,
* because musl doesn't allow rounds >= 20.
*/
if (rounds < B_ROUNDS_MIN) {
rounds = B_ROUNDS_MIN;
}
if (rounds > 19) {
/* rounds = B_ROUNDS_MAX; */
rounds = 19;
}
(void) snprintf (rounds_prefix, sizeof rounds_prefix,
"%2.2ld$", rounds);
return rounds_prefix;
}
#define BCRYPT_SALT_SIZE 22
/*
* Generate a 22 character salt string for bcrypt.
*/
static /*@observer@*/const char *gensalt_bcrypt (void)
{
static char salt[32];
salt[0] = '\0';
seedRNG ();
strcat (salt, l64a (random()));
do {
strcat (salt, l64a (random()));
} while (strlen (salt) < BCRYPT_SALT_SIZE);
salt[BCRYPT_SALT_SIZE] = '\0';
return salt;
}
#endif /* USE_BCRYPT */
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#ifdef USE_YESCRYPT
/* Default cost if not explicitly specified. */
#define Y_COST_DEFAULT 5
/* Minimum cost. */
#define Y_COST_MIN 1
/* Maximum cost. */
#define Y_COST_MAX 11
/*
* Return a salt prefix specifying the cost for the YESCRYPT method.
*/
static /*@observer@*/const char *YESCRYPT_salt_cost (/*@null@*/long *prefered_cost)
{
static char cost_prefix[5];
long cost;
if (NULL == prefered_cost) {
cost = getdef_num ("YESCRYPT_COST_FACTOR", Y_COST_DEFAULT);
} else {
cost = *prefered_cost;
}
if (cost < Y_COST_MIN) {
cost = Y_COST_MIN;
}
if (cost > Y_COST_MAX) {
cost = Y_COST_MAX;
}
cost_prefix[0] = 'j';
if (cost < 3) {
cost_prefix[1] = 0x36 + cost;
} else if (cost < 6) {
cost_prefix[1] = 0x34 + cost;
} else {
cost_prefix[1] = 0x3b + cost;
}
cost_prefix[2] = cost >= 3 ? 'T' : '5';
cost_prefix[3] = '$';
cost_prefix[4] = 0;
return cost_prefix;
}
/*
* Default number of base64 characters used for the salt.
* 24 characters gives a 144 bits (18 bytes) salt. Unlike the more
* traditional 128 bits (16 bytes) salt, this 144 bits salt is always
* represented by the same number of base64 characters without padding
* issue, even with a non-standard base64 encoding scheme.
*/
#define YESCRYPT_SALT_SIZE 24
/*
* Generate a 22 character salt string for yescrypt.
*/
static /*@observer@*/const char *gensalt_yescrypt (void)
{
static char salt[32];
salt[0] = '\0';
seedRNG ();
strcat (salt, l64a (random()));
do {
strcat (salt, l64a (random()));
} while (strlen (salt) < YESCRYPT_SALT_SIZE);
salt[YESCRYPT_SALT_SIZE] = '\0';
return salt;
}
#endif /* USE_YESCRYPT */
/*
* Generate salt of size salt_size.
*/
#define MAX_SALT_SIZE 16
#define MIN_SALT_SIZE 8
static /*@observer@*/const char *gensalt (size_t 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);
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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).
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* * For the YESCRYPT method, this specifies the cost factor (if not NULL).
*/
/*@observer@*/const char *crypt_make_salt (/*@null@*//*@observer@*/const char *meth, /*@null@*/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 {
method = getdef_str ("ENCRYPT_METHOD");
if (NULL == method) {
method = getdef_bool ("MD5_CRYPT_ENAB") ? "MD5" : "DES";
}
}
if (0 == strcmp (method, "MD5")) {
MAGNUM(result, '1');
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#ifdef USE_BCRYPT
} else if (0 == strcmp (method, "BCRYPT")) {
BCRYPTMAGNUM(result);
strcat(result, BCRYPT_salt_rounds((int *)arg));
#endif /* USE_BCRYPT */
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#ifdef USE_YESCRYPT
} else if (0 == strcmp (method, "YESCRYPT")) {
MAGNUM(result, 'y');
strcat(result, YESCRYPT_salt_cost((int *)arg));
#endif /* USE_YESCRYPT */
#ifdef USE_SHA_CRYPT
} else if (0 == strcmp (method, "SHA256")) {
MAGNUM(result, '5');
strcat(result, SHA_salt_rounds((int *)arg));
salt_len = (size_t) shadow_random (8, 16);
} else if (0 == strcmp (method, "SHA512")) {
MAGNUM(result, '6');
strcat(result, SHA_salt_rounds((int *)arg));
salt_len = (size_t) shadow_random (8, 16);
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#endif /* USE_SHA_CRYPT */
} else if (0 != strcmp (method, "DES")) {
fprintf (shadow_logfd,
_("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);
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#ifdef USE_BCRYPT
if (0 == strcmp (method, "BCRYPT")) {
strncat (result, gensalt_bcrypt (),
sizeof (result) - strlen (result) - 1);
return result;
} else {
#endif /* USE_BCRYPT */
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#ifdef USE_YESCRYPT
if (0 == strcmp (method, "YESCRYPT")) {
strncat (result, gensalt_yescrypt (),
sizeof (result) - strlen (result) - 1);
return result;
} else {
#endif /* USE_YESCRYPT */
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strncat (result, gensalt (salt_len),
sizeof (result) - strlen (result) - 1);
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#ifdef USE_YESCRYPT
}
#endif /* USE_YESCRYPT */
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#ifdef USE_BCRYPT
}
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#endif /* USE_BCRYPT */
return result;
}