4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
7 ** May you do good and not evil.
8 ** May you find forgiveness for yourself and forgive others.
9 ** May you share freely, never taking more than you give.
11 *************************************************************************
12 ** This file contains code to implement a pseudo-random number
13 ** generator (PRNG) for SQLite.
15 ** Random numbers are used by some of the database backends in order
16 ** to generate random integer keys for tables or random filenames.
20 #include "sqliteInt.h"
25 ** Get a single 8-bit random value from the RC4 PRNG. The Mutex
26 ** must be held while executing this routine.
28 ** Why not just use a library random generator like lrand48() for this?
29 ** Because the OP_NewRowid opcode in the VDBE depends on having a very
30 ** good source of random numbers. The lrand48() library function may
31 ** well be good enough. But maybe not. Or maybe lrand48() has some
32 ** subtle problems on some systems that could cause problems. It is hard
33 ** to know. To minimize the risk of problems due to bad lrand48()
34 ** implementations, SQLite uses this random number generator based
35 ** on RC4, which we know works very well.
37 ** (Later): Actually, OP_NewRowid does not depend on a good source of
38 ** randomness any more. But we will leave this code in all the same.
40 static int randomByte(){
43 /* All threads share a single random number generator.
44 ** This structure is the current state of the generator.
47 unsigned char isInit
; /* True if initialized */
48 unsigned char i
, j
; /* State variables */
49 unsigned char s
[256]; /* State variables */
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...
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.
66 sqlite3OsRandomSeed(k
);
71 prng
.j
+= prng
.s
[i
] + k
[i
];
73 prng
.s
[prng
.j
] = prng
.s
[i
];
79 /* Generate and return single random byte
84 prng
.s
[prng
.i
] = prng
.s
[prng
.j
];
91 ** Return N random bytes.
93 void sqlite3Randomness(int N
, void *pBuf
){
94 unsigned char *zBuf
= pBuf
;
95 sqlite3OsEnterMutex();
97 *(zBuf
++) = randomByte();
99 sqlite3OsLeaveMutex();