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 41 /* The "wsdPrng" macro will resolve to the pseudo-random number generator 42 ** state vector. If writable static data is unsupported on the target, 43 ** we have to locate the state vector at run-time. In the more common 44 ** case where writable static data is supported, wsdPrng can refer directly 45 ** to the "sqlite3Prng" state vector declared above. 46 */ 47 #ifdef SQLITE_OMIT_WSD 48 struct sqlite3PrngType *p = &GLOBAL(struct sqlite3PrngType, sqlite3Prng); 49 # define wsdPrng p[0] 50 #else 51 # define wsdPrng sqlite3Prng 52 #endif 53 54 #if SQLITE_THREADSAFE 55 sqlite3_mutex *mutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_PRNG); 56 sqlite3_mutex_enter(mutex); 57 #endif 58 59 if( N<=0 || pBuf==0 ){ 60 wsdPrng.isInit = 0; 61 sqlite3_mutex_leave(mutex); 62 return; 63 } 64 65 /* Initialize the state of the random number generator once, 66 ** the first time this routine is called. The seed value does 67 ** not need to contain a lot of randomness since we are not 68 ** trying to do secure encryption or anything like that... 69 ** 70 ** Nothing in this file or anywhere else in SQLite does any kind of 71 ** encryption. The RC4 algorithm is being used as a PRNG (pseudo-random 72 ** number generator) not as an encryption device. 73 */ 74 if( !wsdPrng.isInit ){ 75 int i; 76 char k[256]; 77 wsdPrng.j = 0; 78 wsdPrng.i = 0; 79 sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k); 80 for(i=0; i<256; i++){ 81 wsdPrng.s[i] = (u8)i; 82 } 83 for(i=0; i<256; i++){ 84 wsdPrng.j += wsdPrng.s[i] + k[i]; 85 t = wsdPrng.s[wsdPrng.j]; 86 wsdPrng.s[wsdPrng.j] = wsdPrng.s[i]; 87 wsdPrng.s[i] = t; 88 } 89 wsdPrng.isInit = 1; 90 } 91 92 assert( N>0 ); 93 do{ 94 wsdPrng.i++; 95 t = wsdPrng.s[wsdPrng.i]; 96 wsdPrng.j += t; 97 wsdPrng.s[wsdPrng.i] = wsdPrng.s[wsdPrng.j]; 98 wsdPrng.s[wsdPrng.j] = t; 99 t += wsdPrng.s[wsdPrng.i]; 100 *(zBuf++) = wsdPrng.s[t]; 101 }while( --N ); 102 sqlite3_mutex_leave(mutex); 103 } 104 105 #ifndef SQLITE_OMIT_BUILTIN_TEST 106 /* 107 ** For testing purposes, we sometimes want to preserve the state of 108 ** PRNG and restore the PRNG to its saved state at a later time, or 109 ** to reset the PRNG to its initial state. These routines accomplish 110 ** those tasks. 111 ** 112 ** The sqlite3_test_control() interface calls these routines to 113 ** control the PRNG. 114 */ 115 static SQLITE_WSD struct sqlite3PrngType sqlite3SavedPrng; 116 void sqlite3PrngSaveState(void){ 117 memcpy( 118 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 119 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 120 sizeof(sqlite3Prng) 121 ); 122 } 123 void sqlite3PrngRestoreState(void){ 124 memcpy( 125 &GLOBAL(struct sqlite3PrngType, sqlite3Prng), 126 &GLOBAL(struct sqlite3PrngType, sqlite3SavedPrng), 127 sizeof(sqlite3Prng) 128 ); 129 } 130 #endif /* SQLITE_OMIT_BUILTIN_TEST */ 131