2 * cryptographic random number generator for PuTTY's ssh client
7 void noise_get_heavy(void (*func
) (void *, int));
8 void noise_get_light(void (*func
) (void *, int));
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
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.
27 #define HASHINPUT 64 /* 64 bytes SHA input */
28 #define HASHSIZE 20 /* 160 bits SHA output */
29 #define POOLSIZE 1200 /* size of random pool */
32 unsigned char pool
[POOLSIZE
];
35 unsigned char incoming
[HASHSIZE
];
37 unsigned char incomingb
[HASHINPUT
];
41 static struct RandPool pool
;
43 void random_stir(void) {
44 word32 block
[HASHINPUT
/sizeof(word32
)];
45 word32 digest
[HASHSIZE
/sizeof(word32
)];
48 noise_get_light(random_add_noise
);
50 SHATransform((word32
*)pool
.incoming
, (word32
*)pool
.incomingb
);
54 * Chunks of this code are blatantly endianness-dependent, but
55 * as it's all random bits anyway, WHO CARES?
57 memcpy(digest
, pool
.incoming
, sizeof(digest
));
60 * Make two passes over the pool.
62 for (i
= 0; i
< 2; i
++) {
65 * We operate SHA in CFB mode, repeatedly adding the same
66 * block of data to the digest. But we're also fiddling
67 * with the digest-so-far, so this shouldn't be Bad or
70 memcpy(block
, pool
.pool
, sizeof(block
));
73 * Each pass processes the pool backwards in blocks of
74 * HASHSIZE, just so that in general we get the output of
75 * SHA before the corresponding input, in the hope that
76 * things will be that much less predictable that way
77 * round, when we subsequently return bytes ...
79 for (j
= POOLSIZE
; (j
-= HASHSIZE
) >= 0 ;) {
81 * XOR the bit of the pool we're processing into the
85 for (k
= 0; k
< sizeof(digest
)/sizeof(*digest
); k
++)
86 digest
[k
] ^= ((word32
*)(pool
.pool
+j
))[k
];
89 * Munge our unrevealed first block of the pool into
92 SHATransform(digest
, block
);
95 * Stick the result back into the pool.
98 for (k
= 0; k
< sizeof(digest
)/sizeof(*digest
); k
++)
99 ((word32
*)(pool
.pool
+j
))[k
] = digest
[k
];
104 * Might as well save this value back into `incoming', just so
105 * there'll be some extra bizarreness there.
107 SHATransform(digest
, block
);
108 memcpy(pool
.incoming
, digest
, sizeof(digest
));
110 pool
.poolpos
= sizeof(pool
.incoming
);
113 void random_add_noise(void *noise
, int length
) {
114 unsigned char *p
= noise
;
118 * This function processes HASHINPUT bytes into only HASHSIZE
119 * bytes, so _if_ we were getting incredibly high entropy
120 * sources then we would be throwing away valuable stuff.
122 while (length
>= (HASHINPUT
- pool
.incomingpos
)) {
123 memcpy(pool
.incomingb
+ pool
.incomingpos
, p
,
124 HASHINPUT
- pool
.incomingpos
);
125 p
+= HASHINPUT
- pool
.incomingpos
;
126 length
-= HASHINPUT
- pool
.incomingpos
;
127 SHATransform((word32
*)pool
.incoming
, (word32
*)pool
.incomingb
);
128 for (i
= 0; i
< HASHSIZE
; i
++) {
129 pool
.pool
[pool
.poolpos
++] ^= pool
.incomingb
[i
];
130 if (pool
.poolpos
>= POOLSIZE
)
133 if (pool
.poolpos
< HASHSIZE
)
136 pool
.incomingpos
= 0;
139 memcpy(pool
.incomingb
+ pool
.incomingpos
, p
, length
);
140 pool
.incomingpos
+= length
;
143 void random_add_heavynoise(void *noise
, int length
) {
144 unsigned char *p
= noise
;
147 while (length
>= POOLSIZE
) {
148 for (i
= 0; i
< POOLSIZE
; i
++)
149 pool
.pool
[i
] ^= *p
++;
154 for (i
= 0; i
< length
; i
++)
155 pool
.pool
[i
] ^= *p
++;
159 static void random_add_heavynoise_bitbybit(void *noise
, int length
) {
160 unsigned char *p
= noise
;
163 while (length
>= POOLSIZE
- pool
.poolpos
) {
164 for (i
= 0; i
< POOLSIZE
- pool
.poolpos
; i
++)
165 pool
.pool
[pool
.poolpos
+ i
] ^= *p
++;
167 length
-= POOLSIZE
- pool
.poolpos
;
171 for (i
= 0; i
< length
; i
++)
172 pool
.pool
[i
] ^= *p
++;
176 void random_init(void) {
177 memset(&pool
, 0, sizeof(pool
)); /* just to start with */
179 noise_get_heavy(random_add_heavynoise_bitbybit
);
182 int random_byte(void) {
183 if (pool
.poolpos
>= POOLSIZE
)
186 return pool
.pool
[pool
.poolpos
++];
189 void random_get_savedata(void **data
, int *len
) {
191 *data
= pool
.pool
+pool
.poolpos
;