1/* $OpenBSD: bcrypt_pbkdf.c,v 1.17 2022/12/27 17:10:08 jmc 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 <sys/types.h>
19
20#include <stdint.h>
21#include <stdlib.h>
22#include <blf.h>
23#include <sha2.h>
24#include <string.h>
25#include <util.h>
26
27#define	MINIMUM(a,b) (((a) < (b)) ? (a) : (b))
28
29/*
30 * pkcs #5 pbkdf2 implementation using the "bcrypt" hash
31 *
32 * The bcrypt hash function is derived from the bcrypt password hashing
33 * function with the following modifications:
34 * 1. The input password and salt are preprocessed with SHA512.
35 * 2. The output length is expanded to 256 bits.
36 * 3. Subsequently the magic string to be encrypted is lengthened and modified
37 *    to "OxychromaticBlowfishSwatDynamite"
38 * 4. The hash function is defined to perform 64 rounds of initial state
39 *    expansion. (More rounds are performed by iterating the hash.)
40 *
41 * Note that this implementation pulls the SHA512 operations into the caller
42 * as a performance optimization.
43 *
44 * One modification from official pbkdf2. Instead of outputting key material
45 * linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
46 * generate (e.g.) 512 bits of key material for use as two 256 bit keys, an
47 * attacker can merely run once through the outer loop, but the user
48 * always runs it twice. Shuffling output bytes requires computing the
49 * entirety of the key material to assemble any subkey. This is something a
50 * wise caller could do; we just do it for you.
51 */
52
53#define BCRYPT_WORDS 8
54#define BCRYPT_HASHSIZE (BCRYPT_WORDS * 4)
55
56static void
57bcrypt_hash(uint8_t *sha2pass, uint8_t *sha2salt, uint8_t *out)
58{
59	blf_ctx state;
60	uint8_t ciphertext[BCRYPT_HASHSIZE] =
61	    "OxychromaticBlowfishSwatDynamite";
62	uint32_t cdata[BCRYPT_WORDS];
63	int i;
64	uint16_t j;
65	size_t shalen = SHA512_DIGEST_LENGTH;
66
67	/* key expansion */
68	Blowfish_initstate(&state);
69	Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
70	for (i = 0; i < 64; i++) {
71		Blowfish_expand0state(&state, sha2salt, shalen);
72		Blowfish_expand0state(&state, sha2pass, shalen);
73	}
74
75	/* encryption */
76	j = 0;
77	for (i = 0; i < BCRYPT_WORDS; i++)
78		cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
79		    &j);
80	for (i = 0; i < 64; i++)
81		blf_enc(&state, cdata, BCRYPT_WORDS / 2);
82
83	/* copy out */
84	for (i = 0; i < BCRYPT_WORDS; i++) {
85		out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
86		out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
87		out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
88		out[4 * i + 0] = cdata[i] & 0xff;
89	}
90
91	/* zap */
92	explicit_bzero(ciphertext, sizeof(ciphertext));
93	explicit_bzero(cdata, sizeof(cdata));
94	explicit_bzero(&state, sizeof(state));
95}
96
97int
98bcrypt_pbkdf(const char *pass, size_t passlen, const uint8_t *salt, size_t saltlen,
99    uint8_t *key, size_t keylen, unsigned int rounds)
100{
101	SHA2_CTX ctx;
102	uint8_t sha2pass[SHA512_DIGEST_LENGTH];
103	uint8_t sha2salt[SHA512_DIGEST_LENGTH];
104	uint8_t out[BCRYPT_HASHSIZE];
105	uint8_t tmpout[BCRYPT_HASHSIZE];
106	uint8_t countsalt[4];
107	size_t i, j, amt, stride;
108	uint32_t count;
109	size_t origkeylen = keylen;
110
111	/* nothing crazy */
112	if (rounds < 1)
113		goto bad;
114	if (passlen == 0 || saltlen == 0 || keylen == 0 ||
115	    keylen > sizeof(out) * sizeof(out))
116		goto bad;
117	stride = (keylen + sizeof(out) - 1) / sizeof(out);
118	amt = (keylen + stride - 1) / stride;
119
120	/* collapse password */
121	SHA512Init(&ctx);
122	SHA512Update(&ctx, pass, passlen);
123	SHA512Final(sha2pass, &ctx);
124
125
126	/* generate key, sizeof(out) at a time */
127	for (count = 1; keylen > 0; count++) {
128		countsalt[0] = (count >> 24) & 0xff;
129		countsalt[1] = (count >> 16) & 0xff;
130		countsalt[2] = (count >> 8) & 0xff;
131		countsalt[3] = count & 0xff;
132
133		/* first round, salt is salt */
134		SHA512Init(&ctx);
135		SHA512Update(&ctx, salt, saltlen);
136		SHA512Update(&ctx, countsalt, sizeof(countsalt));
137		SHA512Final(sha2salt, &ctx);
138		bcrypt_hash(sha2pass, sha2salt, tmpout);
139		memcpy(out, tmpout, sizeof(out));
140
141		for (i = 1; i < rounds; i++) {
142			/* subsequent rounds, salt is previous output */
143			SHA512Init(&ctx);
144			SHA512Update(&ctx, tmpout, sizeof(tmpout));
145			SHA512Final(sha2salt, &ctx);
146			bcrypt_hash(sha2pass, sha2salt, tmpout);
147			for (j = 0; j < sizeof(out); j++)
148				out[j] ^= tmpout[j];
149		}
150
151		/*
152		 * pbkdf2 deviation: output the key material non-linearly.
153		 */
154		amt = MINIMUM(amt, keylen);
155		for (i = 0; i < amt; i++) {
156			size_t dest = i * stride + (count - 1);
157			if (dest >= origkeylen)
158				break;
159			key[dest] = out[i];
160		}
161		keylen -= i;
162	}
163
164	/* zap */
165	explicit_bzero(&ctx, sizeof(ctx));
166	explicit_bzero(out, sizeof(out));
167	explicit_bzero(tmpout, sizeof(tmpout));
168
169	return 0;
170
171bad:
172	/* overwrite with random in case caller doesn't check return code */
173	arc4random_buf(key, keylen);
174	return -1;
175}
176