1 | /* $NetBSD: kern_rndpool.c,v 1.16 2015/04/21 04:41:36 riastradh Exp $ */ |
2 | |
3 | /*- |
4 | * Copyright (c) 1997 The NetBSD Foundation, Inc. |
5 | * All rights reserved. |
6 | * |
7 | * This code is derived from software contributed to The NetBSD Foundation |
8 | * by Michael Graff <explorer@flame.org>. This code uses ideas and |
9 | * algorithms from the Linux driver written by Ted Ts'o. |
10 | * |
11 | * Redistribution and use in source and binary forms, with or without |
12 | * modification, are permitted provided that the following conditions |
13 | * are met: |
14 | * 1. Redistributions of source code must retain the above copyright |
15 | * notice, this list of conditions and the following disclaimer. |
16 | * 2. Redistributions in binary form must reproduce the above copyright |
17 | * notice, this list of conditions and the following disclaimer in the |
18 | * documentation and/or other materials provided with the distribution. |
19 | * |
20 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
21 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
22 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
23 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
24 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
25 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
26 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
27 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
28 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
29 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
30 | * POSSIBILITY OF SUCH DAMAGE. |
31 | */ |
32 | |
33 | #include <sys/cdefs.h> |
34 | __KERNEL_RCSID(0, "$NetBSD: kern_rndpool.c,v 1.16 2015/04/21 04:41:36 riastradh Exp $" ); |
35 | |
36 | #include <sys/param.h> |
37 | #include <sys/rndpool.h> |
38 | #include <sys/sha1.h> |
39 | #include <sys/systm.h> |
40 | |
41 | #include <dev/rnd_private.h> |
42 | |
43 | /* |
44 | * The random pool "taps" |
45 | */ |
46 | #define TAP1 99 |
47 | #define TAP2 59 |
48 | #define TAP3 31 |
49 | #define TAP4 9 |
50 | #define TAP5 7 |
51 | |
52 | void |
53 | rndpool_init(rndpool_t *rp) |
54 | { |
55 | |
56 | rp->cursor = 0; |
57 | rp->rotate = 1; |
58 | |
59 | memset(&rp->stats, 0, sizeof(rp->stats)); |
60 | |
61 | rp->stats.curentropy = 0; |
62 | rp->stats.poolsize = RND_POOLWORDS; |
63 | rp->stats.threshold = RND_ENTROPY_THRESHOLD; |
64 | rp->stats.maxentropy = RND_POOLBITS; |
65 | } |
66 | |
67 | u_int32_t |
68 | rndpool_get_entropy_count(rndpool_t *rp) |
69 | { |
70 | |
71 | return (rp->stats.curentropy); |
72 | } |
73 | |
74 | void |
75 | rndpool_set_entropy_count(rndpool_t *rp, u_int32_t count) |
76 | { |
77 | int32_t difference = count - rp->stats.curentropy; |
78 | |
79 | if (__predict_true(difference > 0)) { |
80 | rp->stats.added += difference; |
81 | } |
82 | |
83 | rp->stats.curentropy = count; |
84 | if (rp->stats.curentropy > RND_POOLBITS) { |
85 | rp->stats.discarded += (rp->stats.curentropy - RND_POOLBITS); |
86 | rp->stats.curentropy = RND_POOLBITS; |
87 | } |
88 | } |
89 | |
90 | void rndpool_get_stats(rndpool_t *rp, void *rsp, int size) |
91 | { |
92 | |
93 | memcpy(rsp, &rp->stats, size); |
94 | } |
95 | |
96 | /* |
97 | * The input function treats the contents of the pool as an array of |
98 | * 32 LFSR's of length RND_POOLWORDS, one per bit-plane. The LFSR's |
99 | * are clocked once in parallel, using 32-bit xor operations, for each |
100 | * word to be added. |
101 | * |
102 | * Each word to be added is xor'd with the output word of the LFSR |
103 | * array (one tap at a time). |
104 | * |
105 | * In order to facilitate distribution of entropy between the |
106 | * bit-planes, a 32-bit rotate of this result is performed prior to |
107 | * feedback. The rotation distance is incremented every RND_POOLWORDS |
108 | * clocks, by a value that is relativly prime to the word size to try |
109 | * to spread the bits throughout the pool quickly when the pool is |
110 | * empty. |
111 | * |
112 | * Each LFSR thus takes its feedback from another LFSR, and is |
113 | * effectively re-keyed by both that LFSR and the new data. Feedback |
114 | * occurs with another XOR into the new LFSR, rather than assignment, |
115 | * to avoid destroying any entropy in the destination. |
116 | * |
117 | * Even with zeros as input, the LFSR output data are never visible; |
118 | * the contents of the pool are never divulged except via a hash of |
119 | * the entire pool, so there is no information for correlation |
120 | * attacks. With rotation-based rekeying, each LFSR runs at most a few |
121 | * cycles before being permuted. However, beware of initial |
122 | * conditions when no entropy has been added. |
123 | * |
124 | * The output function also stirs the generated hash back into the |
125 | * pool, further permuting the LFSRs and spreading entropy through the |
126 | * pool. Any unknown bits anywhere in the pool are thus reflected |
127 | * across all the LFSRs after output. |
128 | * |
129 | * (The final XOR assignment into the pool for feedback is equivalent |
130 | * to an additional LFSR tap of the MSB before shifting, in the case |
131 | * where no rotation is done, once every 32 cycles. This LFSR runs for |
132 | * at most one length.) |
133 | */ |
134 | static inline void |
135 | rndpool_add_one_word(rndpool_t *rp, u_int32_t val) |
136 | { |
137 | /* |
138 | * Shifting is implemented using a cursor and taps as offsets, |
139 | * added mod the size of the pool. For this reason, |
140 | * RND_POOLWORDS must be a power of two. |
141 | */ |
142 | val ^= rp->pool[(rp->cursor + TAP1) & (RND_POOLWORDS - 1)]; |
143 | val ^= rp->pool[(rp->cursor + TAP2) & (RND_POOLWORDS - 1)]; |
144 | val ^= rp->pool[(rp->cursor + TAP3) & (RND_POOLWORDS - 1)]; |
145 | val ^= rp->pool[(rp->cursor + TAP4) & (RND_POOLWORDS - 1)]; |
146 | val ^= rp->pool[(rp->cursor + TAP5) & (RND_POOLWORDS - 1)]; |
147 | if (rp->rotate != 0) |
148 | val = ((val << rp->rotate) | (val >> (32 - rp->rotate))); |
149 | rp->pool[rp->cursor++] ^= val; |
150 | |
151 | /* |
152 | * If we have looped around the pool, increment the rotate |
153 | * variable so the next value will get xored in rotated to |
154 | * a different position. |
155 | */ |
156 | if (rp->cursor == RND_POOLWORDS) { |
157 | rp->cursor = 0; |
158 | rp->rotate = (rp->rotate + 7) & 31; |
159 | } |
160 | } |
161 | |
162 | /* |
163 | * Add a buffer's worth of data to the pool. |
164 | */ |
165 | void |
166 | rndpool_add_data(rndpool_t *rp, |
167 | const void * const p, u_int32_t len, u_int32_t entropy) |
168 | { |
169 | u_int32_t val; |
170 | const u_int8_t * buf; |
171 | |
172 | buf = p; |
173 | |
174 | for (; len > 3; len -= 4) { |
175 | (void)memcpy(&val, buf, 4); |
176 | rndpool_add_one_word(rp, val); |
177 | buf += 4; |
178 | } |
179 | |
180 | if (len != 0) { |
181 | val = 0; |
182 | switch (len) { |
183 | case 3: |
184 | val = *buf++; |
185 | case 2: |
186 | val = val << 8 | *buf++; |
187 | case 1: |
188 | val = val << 8 | *buf++; |
189 | } |
190 | |
191 | rndpool_add_one_word(rp, val); |
192 | } |
193 | |
194 | rp->stats.curentropy += entropy; |
195 | rp->stats.added += entropy; |
196 | |
197 | if (rp->stats.curentropy > RND_POOLBITS) { |
198 | rp->stats.discarded += (rp->stats.curentropy - RND_POOLBITS); |
199 | rp->stats.curentropy = RND_POOLBITS; |
200 | } |
201 | } |
202 | |
203 | /* |
204 | * Extract some number of bytes from the random pool, decreasing the |
205 | * estimate of randomness as each byte is extracted. |
206 | * |
207 | * Do this by hashing the pool and returning a part of the hash as |
208 | * randomness. Stir the hash back into the pool. Note that no |
209 | * secrets going back into the pool are given away here since parts of |
210 | * the hash are xored together before being returned. |
211 | * |
212 | * Honor the request from the caller to only return good data, any data, |
213 | * etc. |
214 | * |
215 | * For the "high-quality" mode, we must have as much data as the caller |
216 | * requests, and at some point we must have had at least the "threshold" |
217 | * amount of entropy in the pool. |
218 | */ |
219 | u_int32_t |
220 | (rndpool_t *rp, void *p, u_int32_t len, u_int32_t mode) |
221 | { |
222 | u_int i; |
223 | SHA1_CTX hash; |
224 | u_char digest[SHA1_DIGEST_LENGTH]; |
225 | u_int32_t remain, deltae, count; |
226 | u_int8_t *buf; |
227 | |
228 | buf = p; |
229 | remain = len; |
230 | |
231 | KASSERT(RND_ENTROPY_THRESHOLD * 2 <= sizeof(digest)); |
232 | |
233 | while (remain != 0 && ! (mode == RND_EXTRACT_GOOD && |
234 | remain > rp->stats.curentropy * 8)) { |
235 | /* |
236 | * While bytes are requested, compute the hash of the pool, |
237 | * and then "fold" the hash in half with XOR, keeping the |
238 | * exact hash value secret, as it will be stirred back into |
239 | * the pool. |
240 | * |
241 | * XXX this approach needs examination by competant |
242 | * cryptographers! It's rather expensive per bit but |
243 | * also involves every bit of the pool in the |
244 | * computation of every output bit.. |
245 | */ |
246 | SHA1Init(&hash); |
247 | SHA1Update(&hash, (u_int8_t *)rp->pool, RND_POOLWORDS * 4); |
248 | SHA1Final(digest, &hash); |
249 | |
250 | /* |
251 | * Stir the hash back into the pool. This guarantees |
252 | * that the next hash will generate a different value |
253 | * if no new values were added to the pool. |
254 | */ |
255 | CTASSERT(RND_ENTROPY_THRESHOLD * 2 == SHA1_DIGEST_LENGTH); |
256 | for (i = 0; i < SHA1_DIGEST_LENGTH/4; i++) { |
257 | u_int32_t word; |
258 | memcpy(&word, &digest[i * 4], 4); |
259 | rndpool_add_one_word(rp, word); |
260 | } |
261 | |
262 | /* XXX careful, here the THRESHOLD just controls folding */ |
263 | count = min(remain, RND_ENTROPY_THRESHOLD); |
264 | |
265 | for (i = 0; i < count; i++) |
266 | buf[i] = digest[i] ^ digest[i + RND_ENTROPY_THRESHOLD]; |
267 | |
268 | buf += count; |
269 | deltae = count * 8; |
270 | remain -= count; |
271 | |
272 | deltae = min(deltae, rp->stats.curentropy); |
273 | |
274 | rp->stats.removed += deltae; |
275 | rp->stats.curentropy -= deltae; |
276 | |
277 | if (rp->stats.curentropy == 0) |
278 | rp->stats.generated += (count * 8) - deltae; |
279 | |
280 | } |
281 | |
282 | explicit_memset(&hash, 0, sizeof(hash)); |
283 | explicit_memset(digest, 0, sizeof(digest)); |
284 | |
285 | return (len - remain); |
286 | } |
287 | |