1 /* $OpenBSD: bcrypt_pbkdf.c,v 1.16 2020/08/02 18:35:48 tb 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 /* OPENBSD ORIGINAL: lib/libutil/bcrypt_pbkdf.c */
19
20 /* This version has been modified to use SHA512 from SUPERCOP */
21
22 #include "includes.h"
23
24 #ifndef HAVE_BCRYPT_PBKDF
25
26 #include <sys/types.h>
27
28 #ifdef HAVE_STDLIB_H
29 # include <stdlib.h>
30 #endif
31 #include <string.h>
32
33 #ifdef HAVE_BLF_H
34 # include <blf.h>
35 #endif
36
37 #include "crypto_api.h"
38 #ifdef SHA512_DIGEST_LENGTH
39 # undef SHA512_DIGEST_LENGTH
40 #endif
41 #define SHA512_DIGEST_LENGTH crypto_hash_sha512_BYTES
42
43 #define MINIMUM(a,b) (((a) < (b)) ? (a) : (b))
44
45 /*
46 * pkcs #5 pbkdf2 implementation using the "bcrypt" hash
47 *
48 * The bcrypt hash function is derived from the bcrypt password hashing
49 * function with the following modifications:
50 * 1. The input password and salt are preprocessed with SHA512.
51 * 2. The output length is expanded to 256 bits.
52 * 3. Subsequently the magic string to be encrypted is lengthened and modifed
53 * to "OxychromaticBlowfishSwatDynamite"
54 * 4. The hash function is defined to perform 64 rounds of initial state
55 * expansion. (More rounds are performed by iterating the hash.)
56 *
57 * Note that this implementation pulls the SHA512 operations into the caller
58 * as a performance optimization.
59 *
60 * One modification from official pbkdf2. Instead of outputting key material
61 * linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
62 * generate (e.g.) 512 bits of key material for use as two 256 bit keys, an
63 * attacker can merely run once through the outer loop, but the user
64 * always runs it twice. Shuffling output bytes requires computing the
65 * entirety of the key material to assemble any subkey. This is something a
66 * wise caller could do; we just do it for you.
67 */
68
69 #define BCRYPT_WORDS 8
70 #define BCRYPT_HASHSIZE (BCRYPT_WORDS * 4)
71
72 static void
bcrypt_hash(uint8_t * sha2pass,uint8_t * sha2salt,uint8_t * out)73 bcrypt_hash(uint8_t *sha2pass, uint8_t *sha2salt, uint8_t *out)
74 {
75 blf_ctx state;
76 uint8_t ciphertext[BCRYPT_HASHSIZE] =
77 "OxychromaticBlowfishSwatDynamite";
78 uint32_t cdata[BCRYPT_WORDS];
79 int i;
80 uint16_t j;
81 size_t shalen = SHA512_DIGEST_LENGTH;
82
83 /* key expansion */
84 Blowfish_initstate(&state);
85 Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
86 for (i = 0; i < 64; i++) {
87 Blowfish_expand0state(&state, sha2salt, shalen);
88 Blowfish_expand0state(&state, sha2pass, shalen);
89 }
90
91 /* encryption */
92 j = 0;
93 for (i = 0; i < BCRYPT_WORDS; i++)
94 cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
95 &j);
96 for (i = 0; i < 64; i++)
97 blf_enc(&state, cdata, BCRYPT_WORDS / 2);
98
99 /* copy out */
100 for (i = 0; i < BCRYPT_WORDS; i++) {
101 out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
102 out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
103 out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
104 out[4 * i + 0] = cdata[i] & 0xff;
105 }
106
107 /* zap */
108 explicit_bzero(ciphertext, sizeof(ciphertext));
109 explicit_bzero(cdata, sizeof(cdata));
110 explicit_bzero(&state, sizeof(state));
111 }
112
113 int
bcrypt_pbkdf(const char * pass,size_t passlen,const uint8_t * salt,size_t saltlen,uint8_t * key,size_t keylen,unsigned int rounds)114 bcrypt_pbkdf(const char *pass, size_t passlen, const uint8_t *salt, size_t saltlen,
115 uint8_t *key, size_t keylen, unsigned int rounds)
116 {
117 uint8_t sha2pass[SHA512_DIGEST_LENGTH];
118 uint8_t sha2salt[SHA512_DIGEST_LENGTH];
119 uint8_t out[BCRYPT_HASHSIZE];
120 uint8_t tmpout[BCRYPT_HASHSIZE];
121 uint8_t *countsalt;
122 size_t i, j, amt, stride;
123 uint32_t count;
124 size_t origkeylen = keylen;
125
126 /* nothing crazy */
127 if (rounds < 1)
128 goto bad;
129 if (passlen == 0 || saltlen == 0 || keylen == 0 ||
130 keylen > sizeof(out) * sizeof(out) || saltlen > 1<<20)
131 goto bad;
132 if ((countsalt = calloc(1, saltlen + 4)) == NULL)
133 goto bad;
134 stride = (keylen + sizeof(out) - 1) / sizeof(out);
135 amt = (keylen + stride - 1) / stride;
136
137 memcpy(countsalt, salt, saltlen);
138
139 /* collapse password */
140 crypto_hash_sha512(sha2pass, pass, passlen);
141
142 /* generate key, sizeof(out) at a time */
143 for (count = 1; keylen > 0; count++) {
144 countsalt[saltlen + 0] = (count >> 24) & 0xff;
145 countsalt[saltlen + 1] = (count >> 16) & 0xff;
146 countsalt[saltlen + 2] = (count >> 8) & 0xff;
147 countsalt[saltlen + 3] = count & 0xff;
148
149 /* first round, salt is salt */
150 crypto_hash_sha512(sha2salt, countsalt, saltlen + 4);
151
152 bcrypt_hash(sha2pass, sha2salt, tmpout);
153 memcpy(out, tmpout, sizeof(out));
154
155 for (i = 1; i < rounds; i++) {
156 /* subsequent rounds, salt is previous output */
157 crypto_hash_sha512(sha2salt, tmpout, sizeof(tmpout));
158 bcrypt_hash(sha2pass, sha2salt, tmpout);
159 for (j = 0; j < sizeof(out); j++)
160 out[j] ^= tmpout[j];
161 }
162
163 /*
164 * pbkdf2 deviation: output the key material non-linearly.
165 */
166 amt = MINIMUM(amt, keylen);
167 for (i = 0; i < amt; i++) {
168 size_t dest = i * stride + (count - 1);
169 if (dest >= origkeylen)
170 break;
171 key[dest] = out[i];
172 }
173 keylen -= i;
174 }
175
176 /* zap */
177 freezero(countsalt, saltlen + 4);
178 explicit_bzero(out, sizeof(out));
179 explicit_bzero(tmpout, sizeof(tmpout));
180
181 return 0;
182
183 bad:
184 /* overwrite with random in case caller doesn't check return code */
185 arc4random_buf(key, keylen);
186 return -1;
187 }
188 #endif /* HAVE_BCRYPT_PBKDF */
189