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