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 
19 #ifndef HAVE_BCRYPT_PBKDF
20 
21 #include "libssh2_priv.h"
22 #include <stdlib.h>
23 #include <sys/types.h>
24 #ifdef HAVE_SYS_PARAM_H
25 #include <sys/param.h>
26 #endif
27 
28 #include "blf.h"
29 
30 #define MINIMUM(a,b) (((a) < (b)) ? (a) : (b))
31 
32 /*
33  * pkcs #5 pbkdf2 implementation using the "bcrypt" hash
34  *
35  * The bcrypt hash function is derived from the bcrypt password hashing
36  * function with the following modifications:
37  * 1. The input password and salt are preprocessed with SHA512.
38  * 2. The output length is expanded to 256 bits.
39  * 3. Subsequently the magic string to be encrypted is lengthened and modified
40  *    to "OxychromaticBlowfishSwatDynamite"
41  * 4. The hash function is defined to perform 64 rounds of initial state
42  *    expansion. (More rounds are performed by iterating the hash.)
43  *
44  * Note that this implementation pulls the SHA512 operations into the caller
45  * as a performance optimization.
46  *
47  * One modification from official pbkdf2. Instead of outputting key material
48  * linearly, we mix it. pbkdf2 has a known weakness where if one uses it to
49  * generate (i.e.) 512 bits of key material for use as two 256 bit keys, an
50  * attacker can merely run once through the outer loop below, but the user
51  * always runs it twice. Shuffling output bytes requires computing the
52  * entirety of the key material to assemble any subkey. This is something a
53  * wise caller could do; we just do it for you.
54  */
55 
56 #define BCRYPT_BLOCKS 8
57 #define BCRYPT_HASHSIZE (BCRYPT_BLOCKS * 4)
58 
59 static void
bcrypt_hash(uint8_t * sha2pass,uint8_t * sha2salt,uint8_t * out)60 bcrypt_hash(uint8_t *sha2pass, uint8_t *sha2salt, uint8_t *out)
61 {
62     blf_ctx state;
63     uint8_t ciphertext[BCRYPT_HASHSIZE] =
64         "OxychromaticBlowfishSwatDynamite";
65     uint32_t cdata[BCRYPT_BLOCKS];
66     int i;
67     uint16_t j;
68     size_t shalen = SHA512_DIGEST_LENGTH;
69 
70     /* key expansion */
71     Blowfish_initstate(&state);
72     Blowfish_expandstate(&state, sha2salt, shalen, sha2pass, shalen);
73     for(i = 0; i < 64; i++) {
74         Blowfish_expand0state(&state, sha2salt, shalen);
75         Blowfish_expand0state(&state, sha2pass, shalen);
76     }
77 
78     /* encryption */
79     j = 0;
80     for(i = 0; i < BCRYPT_BLOCKS; i++)
81         cdata[i] = Blowfish_stream2word(ciphertext, sizeof(ciphertext),
82                                         &j);
83     for(i = 0; i < 64; i++)
84         blf_enc(&state, cdata, sizeof(cdata) / sizeof(uint64_t));
85 
86     /* copy out */
87     for(i = 0; i < BCRYPT_BLOCKS; i++) {
88         out[4 * i + 3] = (cdata[i] >> 24) & 0xff;
89         out[4 * i + 2] = (cdata[i] >> 16) & 0xff;
90         out[4 * i + 1] = (cdata[i] >> 8) & 0xff;
91         out[4 * i + 0] = cdata[i] & 0xff;
92     }
93 
94     /* zap */
95     _libssh2_explicit_zero(ciphertext, sizeof(ciphertext));
96     _libssh2_explicit_zero(cdata, sizeof(cdata));
97     _libssh2_explicit_zero(&state, sizeof(state));
98 }
99 
100 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)101 bcrypt_pbkdf(const char *pass, size_t passlen, const uint8_t *salt,
102              size_t saltlen,
103              uint8_t *key, size_t keylen, unsigned int rounds)
104 {
105     uint8_t sha2pass[SHA512_DIGEST_LENGTH];
106     uint8_t sha2salt[SHA512_DIGEST_LENGTH];
107     uint8_t out[BCRYPT_HASHSIZE];
108     uint8_t tmpout[BCRYPT_HASHSIZE];
109     uint8_t *countsalt;
110     size_t i, j, amt, stride;
111     uint32_t count;
112     size_t origkeylen = keylen;
113     libssh2_sha512_ctx ctx;
114 
115     /* nothing crazy */
116     if(rounds < 1)
117         return -1;
118     if(passlen == 0 || saltlen == 0 || keylen == 0 ||
119        keylen > sizeof(out) * sizeof(out) || saltlen > 1<<20)
120         return -1;
121     countsalt = calloc(1, saltlen + 4);
122     if(countsalt == NULL)
123         return -1;
124     stride = (keylen + sizeof(out) - 1) / sizeof(out);
125     amt = (keylen + stride - 1) / stride;
126 
127     memcpy(countsalt, salt, saltlen);
128 
129     /* collapse password */
130     libssh2_sha512_init(&ctx);
131     libssh2_sha512_update(ctx, pass, passlen);
132     libssh2_sha512_final(ctx, sha2pass);
133 
134     /* generate key, sizeof(out) at a time */
135     for(count = 1; keylen > 0; count++) {
136         countsalt[saltlen + 0] = (count >> 24) & 0xff;
137         countsalt[saltlen + 1] = (count >> 16) & 0xff;
138         countsalt[saltlen + 2] = (count >> 8) & 0xff;
139         countsalt[saltlen + 3] = count & 0xff;
140 
141         /* first round, salt is salt */
142         libssh2_sha512_init(&ctx);
143         libssh2_sha512_update(ctx, countsalt, saltlen + 4);
144         libssh2_sha512_final(ctx, sha2salt);
145 
146         bcrypt_hash(sha2pass, sha2salt, tmpout);
147         memcpy(out, tmpout, sizeof(out));
148 
149         for(i = 1; i < rounds; i++) {
150             /* subsequent rounds, salt is previous output */
151             libssh2_sha512_init(&ctx);
152             libssh2_sha512_update(ctx, tmpout, sizeof(tmpout));
153             libssh2_sha512_final(ctx, sha2salt);
154 
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             }
169             key[dest] = out[i];
170         }
171         keylen -= i;
172     }
173 
174     /* zap */
175     _libssh2_explicit_zero(out, sizeof(out));
176     free(countsalt);
177 
178     return 0;
179 }
180 #endif /* HAVE_BCRYPT_PBKDF */
181