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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 | |
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55 | memcpy(pool.incomingb + pool.incomingpos, p, length); |
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56 | pool.incomingpos += length; |
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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); |
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124 | memcpy(pool.incoming, digest, sizeof(digest)); |
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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 | |
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140 | memcpy(pool.pool + pool.poolpos, p, length); |
141 | pool.poolpos += length; |
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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 | } |