/* $$$: arc4random.c 2005/02/08 robert */ /* $NetBSD: arc4random.c,v 1.5.2.1 2004/03/26 22:52:50 jmc Exp $ */ /* $OpenBSD: arc4random.c,v 1.6 2001/06/05 05:05:38 pvalchev Exp $ */ /* * Arc4 random number generator for OpenBSD. * Copyright 1996 David Mazieres . * * Modification and redistribution in source and binary forms is * permitted provided that due credit is given to the author and the * OpenBSD project by leaving this copyright notice intact. */ /* * This code is derived from section 17.1 of Applied Cryptography, * second edition, which describes a stream cipher allegedly * compatible with RSA Labs "RC4" cipher (the actual description of * which is a trade secret). The same algorithm is used as a stream * cipher called "arcfour" in Tatu Ylonen's ssh package. * * Here the stream cipher has been modified always to include the time * when initializing the state. That makes it impossible to * regenerate the same random sequence twice, so this can't be used * for encryption, but will generate good random numbers. * * RC4 is a registered trademark of RSA Laboratories. */ #include #include #include #include #include #include #include #ifdef __ARC4RANDOM_USE_ERANDOM__ #include #endif struct arc4_stream { u_int8_t i; u_int8_t j; u_int8_t s[256]; }; static smallint rs_initialized; static struct arc4_stream rs; static __inline__ void arc4_init(struct arc4_stream *as) { int n; for (n = 0; n < 256; n++) as->s[n] = n; as->i = 0; as->j = 0; } static __inline__ u_int8_t arc4_getbyte(struct arc4_stream *as) { u_int8_t si, sj; as->i = (as->i + 1); si = as->s[as->i]; as->j = (as->j + si); sj = as->s[as->j]; as->s[as->i] = sj; as->s[as->j] = si; return (as->s[(si + sj) & 0xff]); } static __inline__ void arc4_addrandom(struct arc4_stream *as, u_char *dat, int datlen) { int n; u_int8_t si; as->i--; for (n = 0; n < 256; n++) { as->i = (as->i + 1); si = as->s[as->i]; as->j = (as->j + si + dat[n % datlen]); as->s[as->i] = as->s[as->j]; as->s[as->j] = si; } as->j = as->i; } static void arc4_stir(struct arc4_stream *as) { int fd; struct { struct timeval tv; uint rnd[(128 - sizeof(struct timeval)) / sizeof(uint)]; } rdat; int n; gettimeofday(&rdat.tv, NULL); fd = open("/dev/urandom", O_RDONLY); if (fd != -1) { read(fd, rdat.rnd, sizeof(rdat.rnd)); close(fd); } #ifdef __ARC4RANDOM_USE_ERANDOM__ else { int mib[3]; uint i; size_t len; /* Device could not be opened, we might be chrooted, take * randomness from sysctl. */ mib[0] = CTL_KERN; mib[1] = KERN_RANDOM; mib[2] = RANDOM_ERANDOM; for (i = 0; i < sizeof(rdat.rnd) / sizeof(uint); i++) { len = sizeof(uint); if (sysctl(mib, 3, &rdat.rnd[i], &len, NULL, 0) == -1) break; } } #endif arc4_addrandom(as, (void *) &rdat, sizeof(rdat)); /* * Throw away the first N words of output, as suggested in the * paper "Weaknesses in the Key Scheduling Algorithm of RC4" * by Fluher, Mantin, and Shamir. * http://www.wisdom.weizmann.ac.il/~itsik/RC4/Papers/Rc4_ksa.ps * N = 256 in our case. */ for (n = 0; n < 256 * 4; n++) arc4_getbyte(as); } static __inline__ u_int32_t arc4_getword(struct arc4_stream *as) { u_int32_t val; val = arc4_getbyte(as) << 24; val |= arc4_getbyte(as) << 16; val |= arc4_getbyte(as) << 8; val |= arc4_getbyte(as); return val; } static void __arc4random_stir(void) { if (!rs_initialized) { arc4_init(&rs); rs_initialized = 1; } arc4_stir(&rs); } strong_alias(__arc4random_stir,arc4random_stir) void arc4random_addrandom(u_char *dat, int datlen) { if (!rs_initialized) __arc4random_stir(); arc4_addrandom(&rs, dat, datlen); } u_int32_t arc4random(void) { if (!rs_initialized) __arc4random_stir(); return arc4_getword(&rs); } #if 0 /*-------- Test code --------*/ #include #include int main(void) { int random_number; random_number = arc4random() % 65536; printf("%d\n", random_number); return 0; } #endif