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 #ifndef SQLITE_OMIT_AUTOINIT 38 if( sqlite3_initialize() ) return; 39 #endif 40 if( pBuf==0 || N<=0 ) return; 41 42 /* The "wsdPrng" macro will resolve to the pseudo-random number generator 43 ** state vector. If writable static data is unsupported on the target, 44 ** we have to locate the state vector at run-time. In the more common 45 ** case where writable static data is supported, wsdPrng can refer directly 46 ** to the "sqlite3Prng" state vector declared above. 47 */ 48 #ifdef SQLITE_OMIT_WSD 49 struct sqlite3PrngType *p = &GLOBAL(struct sqlite3PrngType, sqlite3Prng); 50 # define wsdPrng p[0] 51 #else 52 # define wsdPrng sqlite3Prng 53 #endif 54 55 #if SQLITE_THREADSAFE 56 sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG); 57 sqlite3_mutex_enter(mutex); 58 #endif 59 60 /* Initialize the state of the random number generator once, 61 ** the first time this routine is called. The seed value does 62 ** not need to contain a lot of randomness since we are not 63 ** trying to do secure encryption or anything like that... 64 ** 65 ** Nothing in this file or anywhere else in SQLite does any kind of 66 ** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random 67 ** number generator) not as an encryption device. 68 */ 69 if( !wsdPrng.isInit ){ 70 int i; 71 char k[256]; 72 wsdPrng.j = 0; 73 wsdPrng.i = 0; 74 sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k); 75 for(i=0; i<256; i++){ 76 wsdPrng.s[i] = (u8)i; 77 } 78 for(i=0; i<256; i++){ 79 wsdPrng.j += wsdPrng.s[i] + k[i]; 80 t = wsdPrng.s[wsdPrng.j]; 81 wsdPrng.s[wsdPrng.j] = wsdPrng.s[i]; 82 wsdPrng.s[i] = t; 83 } 84 wsdPrng.isInit = 1; 85 } 86 87 assert( N>0 ); 88 do{ 89 wsdPrng.i++; 90 t = wsdPrng.s[wsdPrng.i]; 91 wsdPrng.j += t; 92 wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j]; 93 wsdPrng.s[wsdPrng.j] = t; 94 t += wsdPrng.s[wsdPrng.i]; 95 *(zBuf++) = wsdPrng.s[t]; 96 }while( --N ); 97 sqlite3_mutex_leave(mutex); 98 } 99 100 #ifndef SQLITE_OMIT_BUILTIN_TEST 101 /* 102 ** For testing purposes, we sometimes want to preserve the state of 103 ** PRNG and restore the PRNG to its saved state at a later time, or 104 ** to reset the PRNG to its initial state. These routines accomplish 105 ** those tasks. 106 ** 107 ** The sqlite3_test_control() interface calls these routines to 108 ** control the PRNG. 109 */ 110 static SQLITE_WSD struct sqlite3PrngType sqlite3SavedPrng; 111 void sqlite3PrngSaveState(void){ 112 memcpy( 113 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 114 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 115 sizeof(sqlite3Prng) 116 ); 117 } 118 void sqlite3PrngRestoreState(void){ 119 memcpy( 120 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 121 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 122 sizeof(sqlite3Prng) 123 ); 124 } 125 #endif /* SQLITE_OMIT_BUILTIN_TEST */ 126