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2f823fa326
Minor code reorganization was required, but the only functional change was that the first 1024 bytes of output are thrown out after each reseed, rather than just the initial seed.
153 lines
2.9 KiB
C
153 lines
2.9 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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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/random.h>
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#include <sys/libkern.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/time.h>
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#define ARC4_RESEED_BYTES 65536
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#define ARC4_RESEED_SECONDS 300
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#define ARC4_KEYBYTES (256 / 8)
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static u_int8_t arc4_i, arc4_j;
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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 time_t arc4_t_reseed;
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static struct mtx arc4_mtx;
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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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struct timeval tv_now;
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/*
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* XXX read_random() returns unsafe numbers if the entropy
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* device is not loaded -- MarkM.
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*/
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r = read_random(key, ARC4_KEYBYTES);
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getmicrouptime(&tv_now);
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mtx_lock(&arc4_mtx);
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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_t_reseed = tv_now.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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mtx_unlock(&arc4_mtx);
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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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mtx_init(&arc4_mtx, "arc4_mtx", NULL, MTX_DEF);
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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_t_reseed = 0;
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}
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SYSINIT(arc4_init, SI_SUB_LOCK, SI_ORDER_ANY, arc4_init, NULL);
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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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/*
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* MPSAFE
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*/
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void
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arc4rand(void *ptr, u_int len, int reseed)
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{
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u_char *p;
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struct timeval tv;
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getmicrouptime(&tv);
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if (reseed ||
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(arc4_numruns > ARC4_RESEED_BYTES) ||
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(tv.tv_sec > arc4_t_reseed))
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arc4_randomstir();
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mtx_lock(&arc4_mtx);
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arc4_numruns += len;
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p = ptr;
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while (len--)
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*p++ = arc4_randbyte();
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mtx_unlock(&arc4_mtx);
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}
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uint32_t
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arc4random(void)
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{
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uint32_t ret;
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arc4rand(&ret, sizeof ret, 0);
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return ret;
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}
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