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 #include <stdlib.h>
26 #include <string.h>
27 
28 #ifdef HAVE_BLF_H
29 # include <blf.h>
30 #endif
31 
32 #include "crypto_api.h"
33 #ifdef SHA512_DIGEST_LENGTH
34 # undef SHA512_DIGEST_LENGTH
35 #endif
36 #define SHA512_DIGEST_LENGTH crypto_hash_sha512_BYTES
37 
38 #define	MINIMUM(a,b) (((a) < (b)) ? (a) : (b))
39 
40 /*
41  * pkcs #5 pbkdf2 implementation using the "bcrypt" hash
42  *
43  * The bcrypt hash function is derived from the bcrypt password hashing
44  * function with the following modifications:
45  * 1. The input password and salt are preprocessed with SHA512.
46  * 2. The output length is expanded to 256 bits.
47  * 3. Subsequently the magic string to be encrypted is lengthened and modified
48  *    to "OxychromaticBlowfishSwatDynamite"
49  * 4. The hash function is defined to perform 64 rounds of initial state
50  *    expansion. (More rounds are performed by iterating the hash.)
51  *
52  * Note that this implementation pulls the SHA512 operations into the caller
53  * as a performance optimization.
54  *
55  * One modification from official pbkdf2. Instead of outputting key material
56  * linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
57  * generate (e.g.) 512 bits of key material for use as two 256 bit keys, an
58  * attacker can merely run once through the outer loop, but the user
59  * always runs it twice. Shuffling output bytes requires computing the
60  * entirety of the key material to assemble any subkey. This is something a
61  * wise caller could do; we just do it for you.
62  */
63 
64 #define BCRYPT_WORDS 8
65 #define BCRYPT_HASHSIZE (BCRYPT_WORDS * 4)
66 
67 static void
68 bcrypt_hash(u_int8_t *sha2pass, u_int8_t *sha2salt, u_int8_t *out)
69 {
70 	blf_ctx state;
71 	u_int8_t ciphertext[BCRYPT_HASHSIZE] =
72 	    "OxychromaticBlowfishSwatDynamite";
73 	uint32_t cdata[BCRYPT_WORDS];
74 	int i;
75 	uint16_t j;
76 	size_t shalen = SHA512_DIGEST_LENGTH;
77 
78 	/* key expansion */
79 	Blowfish_initstate(&state);
80 	Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
81 	for (i = 0; i < 64; i++) {
82 		Blowfish_expand0state(&state, sha2salt, shalen);
83 		Blowfish_expand0state(&state, sha2pass, shalen);
84 	}
85 
86 	/* encryption */
87 	j = 0;
88 	for (i = 0; i < BCRYPT_WORDS; i++)
89 		cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
90 		    &j);
91 	for (i = 0; i < 64; i++)
92 		blf_enc(&state, cdata, sizeof(cdata) / sizeof(uint64_t));
93 
94 	/* copy out */
95 	for (i = 0; i < BCRYPT_WORDS; i++) {
96 		out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
97 		out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
98 		out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
99 		out[4 * i + 0] = cdata[i] & 0xff;
100 	}
101 
102 	/* zap */
103 	explicit_bzero(ciphertext, sizeof(ciphertext));
104 	explicit_bzero(cdata, sizeof(cdata));
105 	explicit_bzero(&state, sizeof(state));
106 }
107 
108 int
109 bcrypt_pbkdf(const char *pass, size_t passlen, const u_int8_t *salt, size_t saltlen,
110     u_int8_t *key, size_t keylen, unsigned int rounds)
111 {
112 	u_int8_t sha2pass[SHA512_DIGEST_LENGTH];
113 	u_int8_t sha2salt[SHA512_DIGEST_LENGTH];
114 	u_int8_t out[BCRYPT_HASHSIZE];
115 	u_int8_t tmpout[BCRYPT_HASHSIZE];
116 	u_int8_t *countsalt;
117 	size_t i, j, amt, stride;
118 	uint32_t count;
119 	size_t origkeylen = keylen;
120 
121 	/* nothing crazy */
122 	if (rounds < 1)
123 		return -1;
124 	if (passlen == 0 || saltlen == 0 || keylen == 0 ||
125 	    keylen > sizeof(out) * sizeof(out) || saltlen > 1<<20)
126 		return -1;
127 	if ((countsalt = calloc(1, saltlen + 4)) == NULL)
128 		return -1;
129 	stride = (keylen + sizeof(out) - 1) / sizeof(out);
130 	amt = (keylen + stride - 1) / stride;
131 
132 	memcpy(countsalt, salt, saltlen);
133 
134 	/* collapse password */
135 	crypto_hash_sha512(sha2pass, pass, passlen);
136 
137 	/* generate key, sizeof(out) at a time */
138 	for (count = 1; keylen > 0; count++) {
139 		countsalt[saltlen + 0] = (count >> 24) & 0xff;
140 		countsalt[saltlen + 1] = (count >> 16) & 0xff;
141 		countsalt[saltlen + 2] = (count >> 8) & 0xff;
142 		countsalt[saltlen + 3] = count & 0xff;
143 
144 		/* first round, salt is salt */
145 		crypto_hash_sha512(sha2salt, countsalt, saltlen + 4);
146 
147 		bcrypt_hash(sha2pass, sha2salt, tmpout);
148 		memcpy(out, tmpout, sizeof(out));
149 
150 		for (i = 1; i < rounds; i++) {
151 			/* subsequent rounds, salt is previous output */
152 			crypto_hash_sha512(sha2salt, tmpout, sizeof(tmpout));
153 			bcrypt_hash(sha2pass, sha2salt, tmpout);
154 			for (j = 0; j < sizeof(out); j++)
155 				out[j] ^= tmpout[j];
156 		}
157 
158 		/*
159 		 * pbkdf2 deviation: output the key material non-linearly.
160 		 */
161 		amt = MINIMUM(amt, keylen);
162 		for (i = 0; i < amt; i++) {
163 			size_t dest = i * stride + (count - 1);
164 			if (dest >= origkeylen)
165 				break;
166 			key[dest] = out[i];
167 		}
168 		keylen -= i;
169 	}
170 
171 	/* zap */
172 	explicit_bzero(out, sizeof(out));
173 	free(countsalt);
174 
175 	return 0;
176 }
177 #endif /* HAVE_BCRYPT_PBKDF */
178