3a7810bc39
- Decrease reseeding interval from every 64 to every 16384 runs to reduce entropy usage. - Add time based reseeding. (Every 5 minutes.) - Throw away the first 256 words of output as suggested in "Weaknesses in the Key Scheduling Algorithm of RC4." Reviewed by: Mark Murray MFC After: jkh says ok
140 lines
2.6 KiB
C
140 lines
2.6 KiB
C
/*-
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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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* $FreeBSD$
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*/
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#include <sys/types.h>
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#include <sys/random.h>
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#include <sys/libkern.h>
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#include <sys/time.h>
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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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/* XXX read_random() returns unsafe numbers if the entropy
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* devce is not loaded - MarkM
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*/
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r = read_random(key, ARC4_KEYBYTES);
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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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{
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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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{
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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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getmicrotime(&arc4_tv_nextreseed);
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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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/*
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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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/* Now, throw away the first N words out output, as suggested
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* in the paper "Weaknesses in the Key Scheduling Algorithm
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* of RC4" by Fluher, Mantin, and Shamir.
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*
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* (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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* 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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struct timeval tv_now;
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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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/* Get current time. */
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getmicrotime(&tv_now);
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if ((++arc4_numruns > ARC4_MAXRUNS) ||
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(tv_now.tv_sec > arc4_tv_nextreseed.tv_sec))
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{
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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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