| 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 | |