| 1 | /* |
| 2 | * cryptographic random number generator for PuTTY's ssh client |
| 3 | */ |
| 4 | |
| 5 | #include "ssh.h" |
| 6 | |
| 7 | void noise_get_heavy(void (*func) (void *, int)); |
| 8 | void noise_get_light(void (*func) (void *, int)); |
| 9 | |
| 10 | /* |
| 11 | * `pool' itself is a pool of random data which we actually use: we |
| 12 | * return bytes from `pool', at position `poolpos', until `poolpos' |
| 13 | * reaches the end of the pool. At this point we generate more |
| 14 | * random data, by adding noise, stirring well, and resetting |
| 15 | * `poolpos' to point to just past the beginning of the pool (not |
| 16 | * _the_ beginning, since otherwise we'd give away the whole |
| 17 | * contents of our pool, and attackers would just have to guess the |
| 18 | * next lot of noise). |
| 19 | * |
| 20 | * `incomingb' buffers acquired noise data, until it gets full, at |
| 21 | * which point the acquired noise is SHA'ed into `incoming' and |
| 22 | * `incomingb' is cleared. The noise in `incoming' is used as part |
| 23 | * of the noise for each stirring of the pool, in addition to local |
| 24 | * time, process listings, and other such stuff. |
| 25 | */ |
| 26 | |
| 27 | #define HASHINPUT 64 /* 64 bytes SHA input */ |
| 28 | #define HASHSIZE 20 /* 160 bits SHA output */ |
| 29 | #define POOLSIZE 1200 /* size of random pool */ |
| 30 | |
| 31 | struct RandPool { |
| 32 | unsigned char pool[POOLSIZE]; |
| 33 | int poolpos; |
| 34 | |
| 35 | unsigned char incoming[HASHSIZE]; |
| 36 | |
| 37 | unsigned char incomingb[HASHINPUT]; |
| 38 | int incomingpos; |
| 39 | }; |
| 40 | |
| 41 | static struct RandPool pool; |
| 42 | |
| 43 | void random_add_noise(void *noise, int length) { |
| 44 | unsigned char *p = noise; |
| 45 | |
| 46 | while (length >= (HASHINPUT - pool.incomingpos)) { |
| 47 | memcpy(pool.incomingb + pool.incomingpos, p, |
| 48 | HASHINPUT - pool.incomingpos); |
| 49 | p += HASHINPUT - pool.incomingpos; |
| 50 | length -= HASHINPUT - pool.incomingpos; |
| 51 | SHATransform((word32 *)pool.incoming, (word32 *)pool.incomingb); |
| 52 | pool.incomingpos = 0; |
| 53 | } |
| 54 | |
| 55 | memcpy(pool.incomingb + pool.incomingpos, p, length); |
| 56 | pool.incomingpos += length; |
| 57 | } |
| 58 | |
| 59 | void random_stir(void) { |
| 60 | word32 block[HASHINPUT/sizeof(word32)]; |
| 61 | word32 digest[HASHSIZE/sizeof(word32)]; |
| 62 | int i, j, k; |
| 63 | |
| 64 | noise_get_light(random_add_noise); |
| 65 | |
| 66 | SHATransform((word32 *)pool.incoming, (word32 *)pool.incomingb); |
| 67 | pool.incomingpos = 0; |
| 68 | |
| 69 | /* |
| 70 | * Chunks of this code are blatantly endianness-dependent, but |
| 71 | * as it's all random bits anyway, WHO CARES? |
| 72 | */ |
| 73 | memcpy(digest, pool.incoming, sizeof(digest)); |
| 74 | |
| 75 | /* |
| 76 | * Make two passes over the pool. |
| 77 | */ |
| 78 | for (i = 0; i < 2; i++) { |
| 79 | |
| 80 | /* |
| 81 | * We operate SHA in CFB mode, repeatedly adding the same |
| 82 | * block of data to the digest. But we're also fiddling |
| 83 | * with the digest-so-far, so this shouldn't be Bad or |
| 84 | * anything. |
| 85 | */ |
| 86 | memcpy(block, pool.pool, sizeof(block)); |
| 87 | |
| 88 | /* |
| 89 | * Each pass processes the pool backwards in blocks of |
| 90 | * HASHSIZE, just so that in general we get the output of |
| 91 | * SHA before the corresponding input, in the hope that |
| 92 | * things will be that much less predictable that way |
| 93 | * round, when we subsequently return bytes ... |
| 94 | */ |
| 95 | for (j = POOLSIZE; (j -= HASHSIZE) >= 0 ;) { |
| 96 | /* |
| 97 | * XOR the bit of the pool we're processing into the |
| 98 | * digest. |
| 99 | */ |
| 100 | |
| 101 | for (k = 0; k < sizeof(digest)/sizeof(*digest); k++) |
| 102 | digest[k] ^= ((word32 *)(pool.pool+j))[k]; |
| 103 | |
| 104 | /* |
| 105 | * Munge our unrevealed first block of the pool into |
| 106 | * it. |
| 107 | */ |
| 108 | SHATransform(digest, block); |
| 109 | |
| 110 | /* |
| 111 | * Stick the result back into the pool. |
| 112 | */ |
| 113 | |
| 114 | for (k = 0; k < sizeof(digest)/sizeof(*digest); k++) |
| 115 | ((word32 *)(pool.pool+j))[k] = digest[k]; |
| 116 | } |
| 117 | } |
| 118 | |
| 119 | /* |
| 120 | * Might as well save this value back into `incoming', just so |
| 121 | * there'll be some extra bizarreness there. |
| 122 | */ |
| 123 | SHATransform(digest, block); |
| 124 | memcpy(pool.incoming, digest, sizeof(digest)); |
| 125 | |
| 126 | pool.poolpos = sizeof(pool.incoming); |
| 127 | } |
| 128 | |
| 129 | static void random_add_heavynoise(void *noise, int length) { |
| 130 | unsigned char *p = noise; |
| 131 | |
| 132 | while (length >= (POOLSIZE - pool.poolpos)) { |
| 133 | memcpy(pool.pool + pool.poolpos, p, POOLSIZE - pool.poolpos); |
| 134 | p += POOLSIZE - pool.poolpos; |
| 135 | length -= POOLSIZE - pool.poolpos; |
| 136 | random_stir(); |
| 137 | pool.poolpos = 0; |
| 138 | } |
| 139 | |
| 140 | memcpy(pool.pool + pool.poolpos, p, length); |
| 141 | pool.poolpos += length; |
| 142 | } |
| 143 | |
| 144 | void random_init(void) { |
| 145 | memset(&pool, 0, sizeof(pool)); /* just to start with */ |
| 146 | |
| 147 | /* |
| 148 | * For noise_get_heavy, we temporarily use `poolpos' as the |
| 149 | * pointer for addition of noise, rather than extraction of |
| 150 | * random numbers. |
| 151 | */ |
| 152 | pool.poolpos = 0; |
| 153 | noise_get_heavy(random_add_heavynoise); |
| 154 | |
| 155 | random_stir(); |
| 156 | } |
| 157 | |
| 158 | int random_byte(void) { |
| 159 | if (pool.poolpos >= POOLSIZE) |
| 160 | random_stir(); |
| 161 | |
| 162 | return pool.pool[pool.poolpos++]; |
| 163 | } |
| 164 | |
| 165 | void random_get_savedata(void **data, int *len) { |
| 166 | random_stir(); |
| 167 | *data = pool.pool+pool.poolpos; |
| 168 | *len = POOLSIZE/2; |
| 169 | } |