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2c38619b52
One bug fixed: Use getmicrouptime() to trigger reseeds so that we cannot be tricked by a clock being stepped backwards. Express parameters in natural units and with natural names. Don't use struct timeval more than we need to. Various stylistic and readability polishing. Introduce arc4rand(void *ptr, u_int len, int reseed) function which returns a stream of pseudo-random bytes, observing the automatic reseed criteria as well as allowing forced reseeds. Rewrite arc4random() in terms of arc4rand(). Sponsored by: DARPA & NAI Labs.
143 lines
2.6 KiB
C
143 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_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_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 time_t arc4_t_reseed;
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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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/* 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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getmicrouptime(&tv_now);
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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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/*
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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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* 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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* 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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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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/* Initialize array if needed. */
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if (!arc4_initialized)
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arc4_init();
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getmicrouptime(&tv);
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arc4_numruns += len;
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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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p = ptr;
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while (len--)
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*p++ = arc4_randbyte();
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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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