1 /*
2 * Copyright (c) 2013 Ted Unangst <tedu@openbsd.org>
3 *
4 * Permission to use, copy, modify, and distribute this software for any
5 * purpose with or without fee is hereby granted, provided that the above
6 * copyright notice and this permission notice appear in all copies.
7 *
8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
15 */
16
17 #include <sys/types.h>
18 #include <stdlib.h>
19 #include <string.h>
20
21 #include "openbsd-blowfish.h"
22 #include "bcrypt.h"
23 #include "crypto.h"
24
25 #define MINIMUM(a,b) (((a) < (b)) ? (a) : (b))
26
27 /*
28 * pkcs #5 pbkdf2 implementation using the "bcrypt" hash
29 *
30 * The bcrypt hash function is derived from the bcrypt password hashing
31 * function with the following modifications:
32 * 1. The input password and salt are preprocessed with SHA512.
33 * 2. The output length is expanded to 256 bits.
34 * 3. Subsequently the magic string to be encrypted is lengthened and modifed
35 * to "OxychromaticBlowfishSwatDynamite"
36 * 4. The hash function is defined to perform 64 rounds of initial state
37 * expansion. (More rounds are performed by iterating the hash.)
38 *
39 * Note that this implementation pulls the SHA512 operations into the caller
40 * as a performance optimization.
41 *
42 * One modification from official pbkdf2. Instead of outputting key material
43 * linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
44 * generate (e.g.) 512 bits of key material for use as two 256 bit keys, an
45 * attacker can merely run once through the outer loop, but the user
46 * always runs it twice. Shuffling output bytes requires computing the
47 * entirety of the key material to assemble any subkey. This is something a
48 * wise caller could do; we just do it for you.
49 */
50
51 #define BCRYPT_WORDS 8
52 #define BCRYPT_HASHSIZE (BCRYPT_WORDS * 4)
53
54 static void
bcrypt_hash(uint8_t * sha2pass,uint8_t * sha2salt,uint8_t * out)55 bcrypt_hash(uint8_t *sha2pass, uint8_t *sha2salt, uint8_t *out)
56 {
57 blf_ctx state;
58 uint8_t ciphertext[BCRYPT_HASHSIZE] =
59 "OxychromaticBlowfishSwatDynamite";
60 uint32_t cdata[BCRYPT_WORDS];
61 int i;
62 uint16_t j;
63 size_t shalen = SHA512_DIGEST_LENGTH;
64
65 /* key expansion */
66 Blowfish_initstate(&state);
67 Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
68 for (i = 0; i < 64; i++) {
69 Blowfish_expand0state(&state, sha2salt, shalen);
70 Blowfish_expand0state(&state, sha2pass, shalen);
71 }
72
73 /* encryption */
74 j = 0;
75 for (i = 0; i < BCRYPT_WORDS; i++)
76 cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
77 &j);
78 for (i = 0; i < 64; i++)
79 blf_enc(&state, cdata, sizeof(cdata) / sizeof(uint64_t));
80
81 /* copy out */
82 for (i = 0; i < BCRYPT_WORDS; i++) {
83 out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
84 out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
85 out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
86 out[4 * i + 0] = cdata[i] & 0xff;
87 }
88
89 /* zap */
90 pr_memscrub(ciphertext, sizeof(ciphertext));
91 pr_memscrub(cdata, sizeof(cdata));
92 pr_memscrub(&state, sizeof(state));
93 }
94
95 static 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)96 bcrypt_pbkdf(const char *pass, size_t passlen, const uint8_t *salt, size_t saltlen,
97 uint8_t *key, size_t keylen, unsigned int rounds)
98 {
99 SHA512_CTX ctx;
100 uint8_t sha2pass[SHA512_DIGEST_LENGTH];
101 uint8_t sha2salt[SHA512_DIGEST_LENGTH];
102 uint8_t out[BCRYPT_HASHSIZE];
103 uint8_t tmpout[BCRYPT_HASHSIZE];
104 uint8_t countsalt[4];
105 size_t i, j, amt, stride;
106 uint32_t count;
107 size_t origkeylen = keylen;
108
109 /* nothing crazy */
110 if (rounds < 1)
111 return -1;
112 if (passlen == 0 || saltlen == 0 || keylen == 0 ||
113 keylen > sizeof(out) * sizeof(out))
114 return -1;
115 stride = (keylen + sizeof(out) - 1) / sizeof(out);
116 amt = (keylen + stride - 1) / stride;
117
118 /* collapse password */
119 SHA512_Init(&ctx);
120 SHA512_Update(&ctx, pass, passlen);
121 SHA512_Final(sha2pass, &ctx);
122
123
124 /* generate key, sizeof(out) at a time */
125 for (count = 1; keylen > 0; count++) {
126 countsalt[0] = (count >> 24) & 0xff;
127 countsalt[1] = (count >> 16) & 0xff;
128 countsalt[2] = (count >> 8) & 0xff;
129 countsalt[3] = count & 0xff;
130
131 /* first round, salt is salt */
132 SHA512_Init(&ctx);
133 SHA512_Update(&ctx, salt, saltlen);
134 SHA512_Update(&ctx, countsalt, sizeof(countsalt));
135 SHA512_Final(sha2salt, &ctx);
136 bcrypt_hash(sha2pass, sha2salt, tmpout);
137 memcpy(out, tmpout, sizeof(out));
138
139 for (i = 1; i < rounds; i++) {
140 /* subsequent rounds, salt is previous output */
141 SHA512_Init(&ctx);
142 SHA512_Update(&ctx, tmpout, sizeof(tmpout));
143 SHA512_Final(sha2salt, &ctx);
144 bcrypt_hash(sha2pass, sha2salt, tmpout);
145 for (j = 0; j < sizeof(out); j++)
146 out[j] ^= tmpout[j];
147 }
148
149 /*
150 * pbkdf2 deviation: output the key material non-linearly.
151 */
152 amt = MINIMUM(amt, keylen);
153 for (i = 0; i < amt; i++) {
154 size_t dest = i * stride + (count - 1);
155 if (dest >= origkeylen)
156 break;
157 key[dest] = out[i];
158 }
159 keylen -= i;
160 }
161
162 /* zap */
163 pr_memscrub(&ctx, sizeof(ctx));
164 pr_memscrub(out, sizeof(out));
165
166 return 0;
167 }
168
169 static const char *trace_channel = "sftp.bcrypt";
170
sftp_bcrypt_pbkdf2(pool * p,const char * passphrase,size_t passphrase_len,unsigned char * salt,uint32_t salt_len,uint32_t rounds,unsigned char * key,uint32_t key_len)171 int sftp_bcrypt_pbkdf2(pool *p, const char *passphrase,
172 size_t passphrase_len, unsigned char *salt, uint32_t salt_len,
173 uint32_t rounds, unsigned char *key, uint32_t key_len) {
174 int res = 0;
175
176 if (p == NULL ||
177 passphrase == NULL ||
178 salt == NULL) {
179 errno = EINVAL;
180 return -1;
181 }
182
183 if (rounds < 1) {
184 pr_trace_msg(trace_channel, 4, "invalid rounds (%lu) for bcrypt KDF",
185 (unsigned long) rounds);
186 errno = EINVAL;
187 return -1;
188 }
189
190 if (passphrase_len == 0 ||
191 salt_len == 0 ||
192 key_len == 0) {
193 pr_trace_msg(trace_channel, 4,
194 "invalid bcrypt KDF data: passphrase (%lu bytes), salt (%lu bytes), "
195 "or key (%lu bytes)", (unsigned long) passphrase_len,
196 (unsigned long) salt_len, (unsigned long) key_len);
197 errno = EINVAL;
198 return -1;
199 }
200
201 if (key_len < SFTP_BCRYPT_DIGEST_LEN) {
202 pr_trace_msg(trace_channel, 4,
203 "invalid bcrypt KDF data: key (%lu bytes) too short; need at "
204 "least %lu bytes", (unsigned long) key_len,
205 (unsigned long) SFTP_BCRYPT_DIGEST_LEN);
206 errno = EINVAL;
207 return -1;
208 }
209
210 res = bcrypt_pbkdf(passphrase, passphrase_len, salt, salt_len, key, key_len,
211 rounds);
212 if (res < 0) {
213 errno = EINVAL;
214 return -1;
215 }
216
217 return 0;
218 }
219