bcrypt_pbkdf.c revision 262566 
1/* $OpenBSD: bcrypt_pbkdf.c,v 1.4 2013/07/29 00:55:53 tedu Exp $ */
2/*
3 * Copyright (c) 2013 Ted Unangst <tedu@openbsd.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18#include "includes.h"
19
20#ifndef HAVE_BCRYPT_PBKDF
21
22#include <sys/types.h>
23#include <sys/param.h>
24
25#ifdef HAVE_STDLIB_H
26# include <stdlib.h>
27#endif
28#include <string.h>
29
30#ifdef HAVE_BLF_H
31# include <blf.h>
32#endif
33
34#include "crypto_api.h"
35#define SHA512_DIGEST_LENGTH crypto_hash_sha512_BYTES
36
37/*
38 * pkcs #5 pbkdf2 implementation using the "bcrypt" hash
39 *
40 * The bcrypt hash function is derived from the bcrypt password hashing
41 * function with the following modifications:
42 * 1. The input password and salt are preprocessed with SHA512.
43 * 2. The output length is expanded to 256 bits.
44 * 3. Subsequently the magic string to be encrypted is lengthened and modifed
45 *    to "OxychromaticBlowfishSwatDynamite"
46 * 4. The hash function is defined to perform 64 rounds of initial state
47 *    expansion. (More rounds are performed by iterating the hash.)
48 *
49 * Note that this implementation pulls the SHA512 operations into the caller
50 * as a performance optimization.
51 *
52 * One modification from official pbkdf2. Instead of outputting key material
53 * linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
54 * generate (i.e.) 512 bits of key material for use as two 256 bit keys, an
55 * attacker can merely run once through the outer loop below, but the user
56 * always runs it twice. Shuffling output bytes requires computing the
57 * entirety of the key material to assemble any subkey. This is something a
58 * wise caller could do; we just do it for you.
59 */
60
61#define BCRYPT_BLOCKS 8
62#define BCRYPT_HASHSIZE (BCRYPT_BLOCKS * 4)
63
64static void
65bcrypt_hash(u_int8_t *sha2pass, u_int8_t *sha2salt, u_int8_t *out)
66{
67	blf_ctx state;
68	u_int8_t ciphertext[BCRYPT_HASHSIZE] =
69	    "OxychromaticBlowfishSwatDynamite";
70	uint32_t cdata[BCRYPT_BLOCKS];
71	int i;
72	uint16_t j;
73	size_t shalen = SHA512_DIGEST_LENGTH;
74
75	/* key expansion */
76	Blowfish_initstate(&state);
77	Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
78	for (i = 0; i < 64; i++) {
79		Blowfish_expand0state(&state, sha2salt, shalen);
80		Blowfish_expand0state(&state, sha2pass, shalen);
81	}
82
83	/* encryption */
84	j = 0;
85	for (i = 0; i < BCRYPT_BLOCKS; i++)
86		cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
87		    &j);
88	for (i = 0; i < 64; i++)
89		blf_enc(&state, cdata, sizeof(cdata) / sizeof(uint64_t));
90
91	/* copy out */
92	for (i = 0; i < BCRYPT_BLOCKS; i++) {
93		out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
94		out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
95		out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
96		out[4 * i + 0] = cdata[i] & 0xff;
97	}
98
99	/* zap */
100	memset(ciphertext, 0, sizeof(ciphertext));
101	memset(cdata, 0, sizeof(cdata));
102	memset(&state, 0, sizeof(state));
103}
104
105int
106bcrypt_pbkdf(const char *pass, size_t passlen, const u_int8_t *salt, size_t saltlen,
107    u_int8_t *key, size_t keylen, unsigned int rounds)
108{
109	u_int8_t sha2pass[SHA512_DIGEST_LENGTH];
110	u_int8_t sha2salt[SHA512_DIGEST_LENGTH];
111	u_int8_t out[BCRYPT_HASHSIZE];
112	u_int8_t tmpout[BCRYPT_HASHSIZE];
113	u_int8_t *countsalt;
114	size_t i, j, amt, stride;
115	uint32_t count;
116
117	/* nothing crazy */
118	if (rounds < 1)
119		return -1;
120	if (passlen == 0 || saltlen == 0 || keylen == 0 ||
121	    keylen > sizeof(out) * sizeof(out) || saltlen > 1<<20)
122		return -1;
123	if ((countsalt = calloc(1, saltlen + 4)) == NULL)
124		return -1;
125	stride = (keylen + sizeof(out) - 1) / sizeof(out);
126	amt = (keylen + stride - 1) / stride;
127
128	memcpy(countsalt, salt, saltlen);
129
130	/* collapse password */
131	crypto_hash_sha512(sha2pass, pass, passlen);
132
133	/* generate key, sizeof(out) at a time */
134	for (count = 1; keylen > 0; count++) {
135		countsalt[saltlen + 0] = (count >> 24) & 0xff;
136		countsalt[saltlen + 1] = (count >> 16) & 0xff;
137		countsalt[saltlen + 2] = (count >> 8) & 0xff;
138		countsalt[saltlen + 3] = count & 0xff;
139
140		/* first round, salt is salt */
141		crypto_hash_sha512(sha2salt, countsalt, saltlen + 4);
142
143		bcrypt_hash(sha2pass, sha2salt, tmpout);
144		memcpy(out, tmpout, sizeof(out));
145
146		for (i = 1; i < rounds; i++) {
147			/* subsequent rounds, salt is previous output */
148			crypto_hash_sha512(sha2salt, tmpout, sizeof(tmpout));
149			bcrypt_hash(sha2pass, sha2salt, tmpout);
150			for (j = 0; j < sizeof(out); j++)
151				out[j] ^= tmpout[j];
152		}
153
154		/*
155		 * pbkdf2 deviation: ouput the key material non-linearly.
156		 */
157		amt = MIN(amt, keylen);
158		for (i = 0; i < amt; i++)
159			key[i * stride + (count - 1)] = out[i];
160		keylen -= amt;
161	}
162
163	/* zap */
164	memset(out, 0, sizeof(out));
165	memset(countsalt, 0, saltlen + 4);
166	free(countsalt);
167
168	return 0;
169}
170#endif /* HAVE_BCRYPT_PBKDF */
171