crypt-sha1.c revision 1.4 
1/* $NetBSD: crypt-sha1.c,v 1.4 2011/05/09 19:15:28 drochner Exp $ */
2
3/*
4 * Copyright (c) 2004, Juniper Networks, Inc.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the copyright holders nor the names of its
16 *    contributors may be used to endorse or promote products derived
17 *    from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
22 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
23 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
24 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
25 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
26 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
27 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
28 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
29 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 */
31
32#include <sys/cdefs.h>
33#if !defined(lint)
34__RCSID("$NetBSD: crypt-sha1.c,v 1.4 2011/05/09 19:15:28 drochner Exp $");
35#endif /* not lint */
36
37#include <stdlib.h>
38#include <unistd.h>
39#include <stdio.h>
40#include <string.h>
41#include <time.h>
42
43#include <err.h>
44#include "crypt.h"
45
46/*
47 * The default iterations - should take >0s on a fast CPU
48 * but not be insane for a slow CPU.
49 */
50#ifndef CRYPT_SHA1_ITERATIONS
51# define CRYPT_SHA1_ITERATIONS 24680
52#endif
53/*
54 * Support a reasonably? long salt.
55 */
56#ifndef CRYPT_SHA1_SALT_LENGTH
57# define CRYPT_SHA1_SALT_LENGTH 64
58#endif
59
60/*
61 * This may be called from crypt_sha1 or gensalt.
62 *
63 * The value returned will be slightly less than <hint> which defaults
64 * to 24680.  The goals are that the number of iterations should take
65 * non-zero amount of time on a fast cpu while not taking insanely
66 * long on a slow cpu.  The current default will take about 5 seconds
67 * on a 100MHz sparc, and about 0.04 seconds on a 3GHz i386.
68 * The number is varied to frustrate those attempting to generate a
69 * dictionary of pre-computed hashes.
70 */
71unsigned int
72__crypt_sha1_iterations (unsigned int hint)
73{
74    static int once = 1;
75
76    /*
77     * We treat CRYPT_SHA1_ITERATIONS as a hint.
78     * Make it harder for someone to pre-compute hashes for a
79     * dictionary attack by not using the same iteration count for
80     * every entry.
81     */
82
83    if (once) {
84	int pid = getpid();
85
86	srandom(time(NULL) ^ (pid * pid));
87	once = 0;
88    }
89    if (hint == 0)
90	hint = CRYPT_SHA1_ITERATIONS;
91    return hint - (random() % (hint / 4));
92}
93
94/*
95 * UNIX password using hmac_sha1
96 * This is PBKDF1 from RFC 2898, but using hmac_sha1.
97 *
98 * The format of the encrypted password is:
99 * $<tag>$<iterations>$<salt>$<digest>
100 *
101 * where:
102 * 	<tag>		is "sha1"
103 *	<iterations>	is an unsigned int identifying how many rounds
104 * 			have been applied to <digest>.  The number
105 * 			should vary slightly for each password to make
106 * 			it harder to generate a dictionary of
107 * 			pre-computed hashes.  See crypt_sha1_iterations.
108 * 	<salt>		up to 64 bytes of random data, 8 bytes is
109 * 			currently considered more than enough.
110 *	<digest>	the hashed password.
111 *
112 * NOTE:
113 * To be FIPS 140 compliant, the password which is used as a hmac key,
114 * should be between 10 and 20 characters to provide at least 80bits
115 * strength, and avoid the need to hash it before using as the
116 * hmac key.
117 */
118char *
119__crypt_sha1 (const char *pw, const char *salt)
120{
121    static const char *magic = SHA1_MAGIC;
122    static unsigned char hmac_buf[SHA1_SIZE];
123    static char passwd[(2 * sizeof(SHA1_MAGIC)) +
124		       CRYPT_SHA1_SALT_LENGTH + SHA1_SIZE];
125    const char *sp;
126    char *ep;
127    unsigned long ul;
128    int sl;
129    int pl;
130    int dl;
131    unsigned int iterations;
132    unsigned int i;
133
134    /*
135     * Salt format is
136     * $<tag>$<iterations>$salt[$]
137     * If it does not start with $ we use our default iterations.
138     */
139
140    /* If it starts with the magic string, then skip that */
141    if (!strncmp(salt, magic, strlen(magic))) {
142	salt += strlen(magic);
143	/* and get the iteration count */
144	iterations = strtoul(salt, &ep, 10);
145	if (*ep != '$')
146	    return NULL;		/* invalid input */
147	salt = ep + 1;			/* skip over the '$' */
148    } else {
149	iterations = __crypt_sha1_iterations(0);
150    }
151
152    /* It stops at the next '$', max CRYPT_SHA1_ITERATIONS chars */
153    for (sp = salt; *sp && *sp != '$' && sp < (salt + CRYPT_SHA1_ITERATIONS); sp++)
154	continue;
155
156    /* Get the length of the actual salt */
157    sl = sp - salt;
158    pl = strlen(pw);
159
160    /*
161     * Now get to work...
162     * Prime the pump with <salt><magic><iterations>
163     */
164    dl = snprintf(passwd, sizeof (passwd), "%.*s%s%u",
165		  sl, salt, magic, iterations);
166    /*
167     * Then hmac using <pw> as key, and repeat...
168     */
169    __hmac_sha1(passwd, dl, pw, pl, hmac_buf);
170    for (i = 1; i < iterations; i++) {
171	__hmac_sha1(hmac_buf, SHA1_SIZE, pw, pl, hmac_buf);
172    }
173    /* Now output... */
174    pl = snprintf(passwd, sizeof(passwd), "%s%u$%.*s$",
175		  magic, iterations, sl, salt);
176    ep = passwd + pl;
177
178    /* Every 3 bytes of hash gives 24 bits which is 4 base64 chars */
179    for (i = 0; i < SHA1_SIZE - 3; i += 3) {
180	ul = (hmac_buf[i+0] << 16) |
181	    (hmac_buf[i+1] << 8) |
182	    hmac_buf[i+2];
183	__crypt_to64(ep, ul, 4); ep += 4;
184    }
185    /* Only 2 bytes left, so we pad with byte0 */
186    ul = (hmac_buf[SHA1_SIZE - 2] << 16) |
187	(hmac_buf[SHA1_SIZE - 1] << 8) |
188	hmac_buf[0];
189    __crypt_to64(ep, ul, 4); ep += 4;
190    *ep = '\0';
191
192    /* Don't leave anything around in vm they could use. */
193    memset(hmac_buf, 0, sizeof hmac_buf);
194
195    return passwd;
196}
197