142 lines
2.7 KiB
C
142 lines
2.7 KiB
C
/* $NetBSD: arc4random.c,v 1.4 2002/06/14 03:05:46 itojun Exp $ */
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/*-
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* THE BEER-WARE LICENSE
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*
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* <dan@FreeBSD.ORG> wrote this file. As long as you retain this notice you
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* can do whatever you want with this stuff. If we meet some day, and you
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* think this stuff is worth it, you can buy me a beer in return.
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*
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* Dan Moschuk
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*
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* $FreeBSD: src/sys/libkern/arc4random.c,v 1.9 2001/08/30 12:30:58 bde Exp $
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*/
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#include <sys/types.h>
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#include <sys/time.h>
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/systm.h>
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#include <lib/libkern/libkern.h>
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#if NRND > 0
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#include <dev/rnd.h>
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#endif
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#define ARC4_MAXRUNS 16384
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#define ARC4_RESEED_SECONDS 300
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#define ARC4_KEYBYTES 32 /* 256 bit key */
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static u_int8_t arc4_i, arc4_j;
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static int arc4_initialized = 0;
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static int arc4_numruns = 0;
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static u_int8_t arc4_sbox[256];
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static struct timeval arc4_tv_nextreseed;
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static u_int8_t arc4_randbyte(void);
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static __inline void
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arc4_swap(u_int8_t *a, u_int8_t *b)
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{
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u_int8_t c;
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c = *a;
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*a = *b;
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*b = c;
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}
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/*
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* Stir our S-box.
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*/
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static void
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arc4_randomstir(void)
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{
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u_int8_t key[256];
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int r, n;
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#if NRND > 0
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r = rnd_extract_data(key, ARC4_KEYBYTES, RND_EXTRACT_ANY);
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#else
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r = 0; /*XXX*/
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#endif
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/* If r == 0 || -1, just use what was on the stack. */
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if (r > 0) {
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for (n = r; n < sizeof(key); n++)
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key[n] = key[n % r];
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}
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for (n = 0; n < 256; n++) {
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arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
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arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
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}
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/* Reset for next reseed cycle. */
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arc4_tv_nextreseed = mono_time;
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arc4_tv_nextreseed.tv_sec += ARC4_RESEED_SECONDS;
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arc4_numruns = 0;
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/*
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* Throw away the first N words of output, as suggested in the
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* paper "Weaknesses in the Key Scheduling Algorithm of RC4"
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* by Fluher, Mantin, and Shamir. (N = 256 in our case.)
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*/
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for (n = 0; n < 256 * 4; n++)
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arc4_randbyte();
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}
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/*
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* Initialize our S-box to its beginning defaults.
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*/
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static void
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arc4_init(void)
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{
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int n;
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arc4_i = arc4_j = 0;
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for (n = 0; n < 256; n++)
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arc4_sbox[n] = (u_int8_t) n;
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arc4_randomstir();
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arc4_initialized = 1;
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}
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/*
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* Generate a random byte.
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*/
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static u_int8_t
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arc4_randbyte(void)
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{
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u_int8_t arc4_t;
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arc4_i = (arc4_i + 1) % 256;
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arc4_j = (arc4_j + arc4_sbox[arc4_i]) % 256;
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arc4_swap(&arc4_sbox[arc4_i], &arc4_sbox[arc4_j]);
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arc4_t = (arc4_sbox[arc4_i] + arc4_sbox[arc4_j]) % 256;
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return arc4_sbox[arc4_t];
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}
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u_int32_t
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arc4random(void)
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{
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u_int32_t ret;
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/* Initialize array if needed. */
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if (!arc4_initialized)
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arc4_init();
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if ((++arc4_numruns > ARC4_MAXRUNS) ||
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(mono_time.tv_sec > arc4_tv_nextreseed.tv_sec)) {
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arc4_randomstir();
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}
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ret = arc4_randbyte();
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ret |= arc4_randbyte() << 8;
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ret |= arc4_randbyte() << 16;
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ret |= arc4_randbyte() << 24;
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return ret;
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}
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