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; 52 #endif 53 54 #ifndef SQLITE_OMIT_AUTOINIT 55 if( sqlite3_initialize() ) return; 56 #endif 57 58 #if SQLITE_THREADSAFE 59 mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG); 60 sqlite3_mutex_enter(mutex); 61 #endif 62 63 if( N<=0 || pBuf==0 ){ 64 wsdPrng.isInit = 0; 65 #if SQLITE_THREADSAFE 66 sqlite3_mutex_leave(mutex); 67 #endif 68 return; 69 } 70 71 /* Initialize the state of the random number generator once, 72 ** the first time this routine is called. The seed value does 73 ** not need to contain a lot of randomness since we are not 74 ** trying to do secure encryption or anything like that... 75 ** 76 ** Nothing in this file or anywhere else in SQLite does any kind of 77 ** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random 78 ** number generator) not as an encryption device. 79 */ 80 if( !wsdPrng.isInit ){ 81 int i; 82 char k[256]; 83 wsdPrng.j = 0; 84 wsdPrng.i = 0; 85 sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k); 86 for(i=0; i<256; i++){ 87 wsdPrng.s[i] = (u8)i; 88 } 89 for(i=0; i<256; i++){ 90 wsdPrng.j += wsdPrng.s[i] + k[i]; 91 t = wsdPrng.s[wsdPrng.j]; 92 wsdPrng.s[wsdPrng.j] = wsdPrng.s[i]; 93 wsdPrng.s[i] = t; 94 } 95 wsdPrng.isInit = 1; 96 } 97 98 assert( N>0 ); 99 do{ 100 wsdPrng.i++; 101 t = wsdPrng.s[wsdPrng.i]; 102 wsdPrng.j += t; 103 wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j]; 104 wsdPrng.s[wsdPrng.j] = t; 105 t += wsdPrng.s[wsdPrng.i]; 106 *(zBuf++) = wsdPrng.s[t]; 107 }while( --N ); 108 sqlite3_mutex_leave(mutex); 109 } 110 111 #ifndef SQLITE_OMIT_BUILTIN_TEST 112 /* 113 ** For testing purposes, we sometimes want to preserve the state of 114 ** PRNG and restore the PRNG to its saved state at a later time, or 115 ** to reset the PRNG to its initial state. These routines accomplish 116 ** those tasks. 117 ** 118 ** The sqlite3_test_control() interface calls these routines to 119 ** control the PRNG. 120 */ 121 static SQLITE_WSD struct sqlite3PrngType sqlite3SavedPrng; 122 void sqlite3PrngSaveState(void){ 123 memcpy( 124 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 125 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 126 sizeof(sqlite3Prng) 127 ); 128 } 129 void sqlite3PrngRestoreState(void){ 130 memcpy( 131 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 132 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 133 sizeof(sqlite3Prng) 134 ); 135 } 136 #endif /* SQLITE_OMIT_BUILTIN_TEST */ 137