1 /* 2 ** 2001 September 15 3 ** 4 ** The author disclaims copyright to this source code. In place of 5 ** a legal notice, here is a blessing: 6 ** 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. 10 ** 11 ************************************************************************* 12 ** This file contains code to implement a pseudo-random number 13 ** generator (PRNG) for SQLite. 14 ** 15 ** Random numbers are used by some of the database backends in order 16 ** to generate random integer keys for tables or random filenames. 17 */ 18 #include "sqliteInt.h" 19 20 21 /* All threads share a single random number generator. 22 ** This structure is the current state of the generator. 23 */ 24 static SQLITE_WSD struct sqlite3PrngType { 25 unsigned char isInit; /* True if initialized */ 26 unsigned char i, j; /* State variables */ 27 unsigned char s[256]; /* State variables */ 28 } sqlite3Prng; 29 30 /* 31 ** Return N random bytes. 32 */ 33 void sqlite3_randomness(int N, void *pBuf){ 34 unsigned char t; 35 unsigned char *zBuf = pBuf; 36 37 /* The "wsdPrng" macro will resolve to the pseudo-random number generator 38 ** state vector. If writable static data is unsupported on the target, 39 ** we have to locate the state vector at run-time. In the more common 40 ** case where writable static data is supported, wsdPrng can refer directly 41 ** to the "sqlite3Prng" state vector declared above. 42 */ 43 #ifdef SQLITE_OMIT_WSD 44 struct sqlite3PrngType *p = &GLOBAL(struct sqlite3PrngType, sqlite3Prng); 45 # define wsdPrng p[0] 46 #else 47 # define wsdPrng sqlite3Prng 48 #endif 49 50 #if SQLITE_THREADSAFE 51 sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG); 52 sqlite3_mutex_enter(mutex); 53 #endif 54 55 /* Initialize the state of the random number generator once, 56 ** the first time this routine is called. The seed value does 57 ** not need to contain a lot of randomness since we are not 58 ** trying to do secure encryption or anything like that... 59 ** 60 ** Nothing in this file or anywhere else in SQLite does any kind of 61 ** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random 62 ** number generator) not as an encryption device. 63 */ 64 if( !wsdPrng.isInit ){ 65 int i; 66 char k[256]; 67 wsdPrng.j = 0; 68 wsdPrng.i = 0; 69 sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k); 70 for(i=0; i<256; i++){ 71 wsdPrng.s[i] = (u8)i; 72 } 73 for(i=0; i<256; i++){ 74 wsdPrng.j += wsdPrng.s[i] + k[i]; 75 t = wsdPrng.s[wsdPrng.j]; 76 wsdPrng.s[wsdPrng.j] = wsdPrng.s[i]; 77 wsdPrng.s[i] = t; 78 } 79 wsdPrng.isInit = 1; 80 } 81 82 while( N-- ){ 83 wsdPrng.i++; 84 t = wsdPrng.s[wsdPrng.i]; 85 wsdPrng.j += t; 86 wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j]; 87 wsdPrng.s[wsdPrng.j] = t; 88 t += wsdPrng.s[wsdPrng.i]; 89 *(zBuf++) = wsdPrng.s[t]; 90 } 91 sqlite3_mutex_leave(mutex); 92 } 93 94 #ifndef SQLITE_OMIT_BUILTIN_TEST 95 /* 96 ** For testing purposes, we sometimes want to preserve the state of 97 ** PRNG and restore the PRNG to its saved state at a later time, or 98 ** to reset the PRNG to its initial state. These routines accomplish 99 ** those tasks. 100 ** 101 ** The sqlite3_test_control() interface calls these routines to 102 ** control the PRNG. 103 */ 104 static SQLITE_WSD struct sqlite3PrngType sqlite3SavedPrng; 105 void sqlite3PrngSaveState(void){ 106 memcpy( 107 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 108 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 109 sizeof(sqlite3Prng) 110 ); 111 } 112 void sqlite3PrngRestoreState(void){ 113 memcpy( 114 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 115 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 116 sizeof(sqlite3Prng) 117 ); 118 } 119 void sqlite3PrngResetState(void){ 120 GLOBAL(struct sqlite3PrngType, sqlite3Prng).isInit = 0; 121 } 122 #endif /* SQLITE_OMIT_BUILTIN_TEST */ 123