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
64 static void
bcrypt_hash(u_int8_t * sha2pass,u_int8_t * sha2salt,u_int8_t * out)65 bcrypt_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
105 int
bcrypt_pbkdf(const char * pass,size_t passlen,const u_int8_t * salt,size_t saltlen,u_int8_t * key,size_t keylen,unsigned int rounds)106 bcrypt_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