1 /*
2 ---------------------------------------------------------------------------
3 Copyright (c) 2002, Dr Brian Gladman < >, Worcester, UK.
4 All rights reserved.
5
6 LICENSE TERMS
7
8 The free distribution and use of this software in both source and binary
9 form is allowed (with or without changes) provided that:
10
11 1. distributions of this source code include the above copyright
12 notice, this list of conditions and the following disclaimer;
13
14 2. distributions in binary form include the above copyright
15 notice, this list of conditions and the following disclaimer
16 in the documentation and/or other associated materials;
17
18 3. the copyright holder's name is not used to endorse products
19 built using this software without specific written permission.
20
21 ALTERNATIVELY, provided that this notice is retained in full, this product
22 may be distributed under the terms of the GNU General Public License (GPL),
23 in which case the provisions of the GPL apply INSTEAD OF those given above.
24
25 DISCLAIMER
26
27 This software is provided 'as is' with no explicit or implied warranties
28 in respect of its properties, including, but not limited to, correctness
29 and/or fitness for purpose.
30 ---------------------------------------------------------------------------
31 Issue Date: 24/01/2003
32
33 This file implements a random data pool based on the use of an external
34 entropy function. It is based on the ideas advocated by Peter Gutmann in
35 his work on pseudo random sequence generators. It is not a 'paranoid'
36 random sequence generator and no attempt is made to protect the pool
37 from prying eyes either by memory locking or by techniques to obscure
38 its location in memory.
39 */
40
41 #include <memory.h>
42 #include "prng.h"
43
44 /* mix a random data pool using the SHA1 compression function (as */
45 /* suggested by Peter Gutmann in his paper on random pools) */
46
prng_mix(unsigned char buf[])47 static void prng_mix(unsigned char buf[])
48 { unsigned int i, len;
49 sha1_ctx ctx[1];
50
51 /*lint -e{663} unusual array to pointer conversion */
52 for(i = 0; i < PRNG_POOL_SIZE; i += SHA1_DIGEST_SIZE)
53 {
54 /* copy digest size pool block into SHA1 hash block */
55 memcpy(ctx->hash, buf + (i ? i : PRNG_POOL_SIZE)
56 - SHA1_DIGEST_SIZE, SHA1_DIGEST_SIZE);
57
58 /* copy data from pool into the SHA1 data buffer */
59 len = PRNG_POOL_SIZE - i;
60 memcpy(ctx->wbuf, buf + i, (len > SHA1_BLOCK_SIZE ? SHA1_BLOCK_SIZE : len));
61
62 if(len < SHA1_BLOCK_SIZE)
63 memcpy(((char*)ctx->wbuf) + len, buf, SHA1_BLOCK_SIZE - len);
64
65 /* compress using the SHA1 compression function */
66 sha1_compile(ctx);
67
68 /* put digest size block back into the random pool */
69 memcpy(buf + i, ctx->hash, SHA1_DIGEST_SIZE);
70 }
71 }
72
73 /* refresh the output buffer and update the random pool by adding */
74 /* entropy and remixing */
75
update_pool(prng_ctx ctx[1])76 static void update_pool(prng_ctx ctx[1])
77 { unsigned int i = 0;
78
79 /* transfer random pool data to the output buffer */
80 memcpy(ctx->obuf, ctx->rbuf, PRNG_POOL_SIZE);
81
82 /* enter entropy data into the pool */
83 while(i < PRNG_POOL_SIZE)
84 i += ctx->entropy(ctx->rbuf + i, PRNG_POOL_SIZE - i);
85
86 /* invert and xor the original pool data into the pool */
87 for(i = 0; i < PRNG_POOL_SIZE; ++i)
88 ctx->rbuf[i] ^= ~ctx->obuf[i];
89
90 /* mix the pool and the output buffer */
91 prng_mix(ctx->rbuf);
92 prng_mix(ctx->obuf);
93 }
94
prng_init(prng_entropy_fn fun,prng_ctx ctx[1])95 void prng_init(prng_entropy_fn fun, prng_ctx ctx[1])
96 { int i;
97
98 /* clear the buffers and the counter in the context */
99 memset(ctx, 0, sizeof(prng_ctx));
100
101 /* set the pointer to the entropy collection function */
102 ctx->entropy = fun;
103
104 /* initialise the random data pool */
105 update_pool(ctx);
106
107 /* mix the pool a minimum number of times */
108 for(i = 0; i < PRNG_MIN_MIX; ++i)
109 prng_mix(ctx->rbuf);
110
111 /* update the pool to prime the pool output buffer */
112 update_pool(ctx);
113 }
114
115 /* provide random bytes from the random data pool */
116
prng_rand(unsigned char data[],unsigned int data_len,prng_ctx ctx[1])117 void prng_rand(unsigned char data[], unsigned int data_len, prng_ctx ctx[1])
118 { unsigned char *rp = data;
119 unsigned int len, pos = ctx->pos;
120
121 while(data_len)
122 {
123 /* transfer 'data_len' bytes (or the number of bytes remaining */
124 /* the pool output buffer if less) into the output */
125 len = (data_len < PRNG_POOL_SIZE - pos ? data_len : PRNG_POOL_SIZE - pos);
126 memcpy(rp, ctx->obuf + pos, len);
127 rp += len; /* update ouput buffer position pointer */
128 pos += len; /* update pool output buffer pointer */
129 data_len -= len; /* update the remaining data count */
130
131 /* refresh the random pool if necessary */
132 if(pos == PRNG_POOL_SIZE)
133 {
134 update_pool(ctx); pos = 0;
135 }
136 }
137
138 ctx->pos = pos;
139 }
140
prng_end(prng_ctx ctx[1])141 void prng_end(prng_ctx ctx[1])
142 {
143 /* ensure the data in the context is destroyed */
144 memset(ctx, 0, sizeof(prng_ctx));
145 }
146
147