bcrypt_pbkdf.c revision 295367 
1/* $OpenBSD: bcrypt_pbkdf.c,v 1.13 2015/01/12 03:20:04 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#ifdef SHA512_DIGEST_LENGTH
36# undef SHA512_DIGEST_LENGTH
37#endif
38#define SHA512_DIGEST_LENGTH crypto_hash_sha512_BYTES
39
40#define	MINIMUM(a,b) (((a) < (b)) ? (a) : (b))
41
42/*
43 * pkcs #5 pbkdf2 implementation using the "bcrypt" hash
44 *
45 * The bcrypt hash function is derived from the bcrypt password hashing
46 * function with the following modifications:
47 * 1. The input password and salt are preprocessed with SHA512.
48 * 2. The output length is expanded to 256 bits.
49 * 3. Subsequently the magic string to be encrypted is lengthened and modifed
50 *    to "OxychromaticBlowfishSwatDynamite"
51 * 4. The hash function is defined to perform 64 rounds of initial state
52 *    expansion. (More rounds are performed by iterating the hash.)
53 *
54 * Note that this implementation pulls the SHA512 operations into the caller
55 * as a performance optimization.
56 *
57 * One modification from official pbkdf2. Instead of outputting key material
58 * linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
59 * generate (e.g.) 512 bits of key material for use as two 256 bit keys, an
60 * attacker can merely run once through the outer loop, but the user
61 * always runs it twice. Shuffling output bytes requires computing the
62 * entirety of the key material to assemble any subkey. This is something a
63 * wise caller could do; we just do it for you.
64 */
65
66#define BCRYPT_WORDS 8
67#define BCRYPT_HASHSIZE (BCRYPT_WORDS * 4)
68
69static void
70bcrypt_hash(u_int8_t *sha2pass, u_int8_t *sha2salt, u_int8_t *out)
71{
72	blf_ctx state;
73	u_int8_t ciphertext[BCRYPT_HASHSIZE] =
74	    "OxychromaticBlowfishSwatDynamite";
75	uint32_t cdata[BCRYPT_WORDS];
76	int i;
77	uint16_t j;
78	size_t shalen = SHA512_DIGEST_LENGTH;
79
80	/* key expansion */
81	Blowfish_initstate(&state);
82	Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
83	for (i = 0; i < 64; i++) {
84		Blowfish_expand0state(&state, sha2salt, shalen);
85		Blowfish_expand0state(&state, sha2pass, shalen);
86	}
87
88	/* encryption */
89	j = 0;
90	for (i = 0; i < BCRYPT_WORDS; i++)
91		cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
92		    &j);
93	for (i = 0; i < 64; i++)
94		blf_enc(&state, cdata, sizeof(cdata) / sizeof(uint64_t));
95
96	/* copy out */
97	for (i = 0; i < BCRYPT_WORDS; i++) {
98		out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
99		out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
100		out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
101		out[4 * i + 0] = cdata[i] & 0xff;
102	}
103
104	/* zap */
105	explicit_bzero(ciphertext, sizeof(ciphertext));
106	explicit_bzero(cdata, sizeof(cdata));
107	explicit_bzero(&state, sizeof(state));
108}
109
110int
111bcrypt_pbkdf(const char *pass, size_t passlen, const u_int8_t *salt, size_t saltlen,
112    u_int8_t *key, size_t keylen, unsigned int rounds)
113{
114	u_int8_t sha2pass[SHA512_DIGEST_LENGTH];
115	u_int8_t sha2salt[SHA512_DIGEST_LENGTH];
116	u_int8_t out[BCRYPT_HASHSIZE];
117	u_int8_t tmpout[BCRYPT_HASHSIZE];
118	u_int8_t *countsalt;
119	size_t i, j, amt, stride;
120	uint32_t count;
121	size_t origkeylen = keylen;
122
123	/* nothing crazy */
124	if (rounds < 1)
125		return -1;
126	if (passlen == 0 || saltlen == 0 || keylen == 0 ||
127	    keylen > sizeof(out) * sizeof(out) || saltlen > 1<<20)
128		return -1;
129	if ((countsalt = calloc(1, saltlen + 4)) == NULL)
130		return -1;
131	stride = (keylen + sizeof(out) - 1) / sizeof(out);
132	amt = (keylen + stride - 1) / stride;
133
134	memcpy(countsalt, salt, saltlen);
135
136	/* collapse password */
137	crypto_hash_sha512(sha2pass, pass, passlen);
138
139	/* generate key, sizeof(out) at a time */
140	for (count = 1; keylen > 0; count++) {
141		countsalt[saltlen + 0] = (count >> 24) & 0xff;
142		countsalt[saltlen + 1] = (count >> 16) & 0xff;
143		countsalt[saltlen + 2] = (count >> 8) & 0xff;
144		countsalt[saltlen + 3] = count & 0xff;
145
146		/* first round, salt is salt */
147		crypto_hash_sha512(sha2salt, countsalt, saltlen + 4);
148
149		bcrypt_hash(sha2pass, sha2salt, tmpout);
150		memcpy(out, tmpout, sizeof(out));
151
152		for (i = 1; i < rounds; i++) {
153			/* subsequent rounds, salt is previous output */
154			crypto_hash_sha512(sha2salt, tmpout, sizeof(tmpout));
155			bcrypt_hash(sha2pass, sha2salt, tmpout);
156			for (j = 0; j < sizeof(out); j++)
157				out[j] ^= tmpout[j];
158		}
159
160		/*
161		 * pbkdf2 deviation: output the key material non-linearly.
162		 */
163		amt = MINIMUM(amt, keylen);
164		for (i = 0; i < amt; i++) {
165			size_t dest = i * stride + (count - 1);
166			if (dest >= origkeylen)
167				break;
168			key[dest] = out[i];
169		}
170		keylen -= i;
171	}
172
173	/* zap */
174	explicit_bzero(out, sizeof(out));
175	free(countsalt);
176
177	return 0;
178}
179#endif /* HAVE_BCRYPT_PBKDF */
180