Minor improvements to arc4random():
- 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
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=82543
@ -13,13 +13,19 @@
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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 64
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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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@ -43,7 +49,7 @@ arc4_randomstir (void)
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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, sizeof(key));
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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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@ -56,6 +62,11 @@ arc4_randomstir (void)
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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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@ -72,6 +83,15 @@ arc4_init(void)
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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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@ -95,14 +115,19 @@ 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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if (++arc4_numruns > ARC4_MAXRUNS)
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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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arc4_numruns = 0;
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}
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ret = arc4_randbyte();
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