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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 modified
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 
69 static void
bcrypt_hash(u_int8_t * sha2pass,u_int8_t * sha2salt,u_int8_t * out)70 bcrypt_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 
110 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)111 bcrypt_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