1
2 #pragma ident "%Z%%M% %I% %E% SMI"
3
4 /*
5 ** 2001 September 15
6 **
7 ** The author disclaims copyright to this source code. In place of
8 ** a legal notice, here is a blessing:
9 **
10 ** May you do good and not evil.
11 ** May you find forgiveness for yourself and forgive others.
12 ** May you share freely, never taking more than you give.
13 **
14 *************************************************************************
15 ** This file contains code to implement a pseudo-random number
16 ** generator (PRNG) for SQLite.
17 **
18 ** Random numbers are used by some of the database backends in order
19 ** to generate random integer keys for tables or random filenames.
20 **
21 ** $Id: random.c,v 1.11 2004/02/11 09:46:33 drh Exp $
22 */
23 #include "sqliteInt.h"
24 #include "os.h"
25
26
27 /*
28 ** Get a single 8-bit random value from the RC4 PRNG. The Mutex
29 ** must be held while executing this routine.
30 **
31 ** Why not just use a library random generator like lrand48() for this?
32 ** Because the OP_NewRecno opcode in the VDBE depends on having a very
33 ** good source of random numbers. The lrand48() library function may
34 ** well be good enough. But maybe not. Or maybe lrand48() has some
35 ** subtle problems on some systems that could cause problems. It is hard
36 ** to know. To minimize the risk of problems due to bad lrand48()
37 ** implementations, SQLite uses this random number generator based
38 ** on RC4, which we know works very well.
39 */
randomByte()40 static int randomByte(){
41 unsigned char t;
42
43 /* All threads share a single random number generator.
44 ** This structure is the current state of the generator.
45 */
46 static struct {
47 unsigned char isInit; /* True if initialized */
48 unsigned char i, j; /* State variables */
49 unsigned char s[256]; /* State variables */
50 } prng;
51
52 /* Initialize the state of the random number generator once,
53 ** the first time this routine is called. The seed value does
54 ** not need to contain a lot of randomness since we are not
55 ** trying to do secure encryption or anything like that...
56 **
57 ** Nothing in this file or anywhere else in SQLite does any kind of
58 ** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random
59 ** number generator) not as an encryption device.
60 */
61 if( !prng.isInit ){
62 int i;
63 char k[256];
64 prng.j = 0;
65 prng.i = 0;
66 sqliteOsRandomSeed(k);
67 for(i=0; i<256; i++){
68 prng.s[i] = i;
69 }
70 for(i=0; i<256; i++){
71 prng.j += prng.s[i] + k[i];
72 t = prng.s[prng.j];
73 prng.s[prng.j] = prng.s[i];
74 prng.s[i] = t;
75 }
76 prng.isInit = 1;
77 }
78
79 /* Generate and return single random byte
80 */
81 prng.i++;
82 t = prng.s[prng.i];
83 prng.j += t;
84 prng.s[prng.i] = prng.s[prng.j];
85 prng.s[prng.j] = t;
86 t += prng.s[prng.i];
87 return prng.s[t];
88 }
89
90 /*
91 ** Return N random bytes.
92 */
sqliteRandomness(int N,void * pBuf)93 void sqliteRandomness(int N, void *pBuf){
94 unsigned char *zBuf = pBuf;
95 sqliteOsEnterMutex();
96 while( N-- ){
97 *(zBuf++) = randomByte();
98 }
99 sqliteOsLeaveMutex();
100 }
101