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1) Initialize arc4_i and arc4_j to 0 after key mixing as recommended in

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draft-kaukonen-cipher-arcfour-03.txt (3.1.5)

2) Drop first 768 bytes as standard RC4-drop(768)
This commit is contained in:
Andrey A. Chernov 2008-07-22 16:16:51 +00:00
parent f1cb603072
commit d16863efa6
1 changed files with 7 additions and 4 deletions
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11
sys/libkern/arc4random.c
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@ -69,18 +69,21 @@ arc4_randomstir (void)
arc4_j = (arc4_j + arc4_sbox[n] + key[n]) % 256;
arc4_swap(&arc4_sbox[n], &arc4_sbox[arc4_j]);
}
arc4_i = arc4_j = 0;
/* Reset for next reseed cycle. */
arc4_t_reseed = tv_now.tv_sec + ARC4_RESEED_SECONDS;
arc4_numruns = 0;
/*
* Throw away the first N words of output, as suggested in the
* Throw away the first N bytes of output, as suggested in the
* paper "Weaknesses in the Key Scheduling Algorithm of RC4"
* by Fluher, Mantin, and Shamir. (N = 256 in our case.)
* by Fluher, Mantin, and Shamir. N=768 is based on
* suggestions in the paper "(Not So) Random Shuffles of RC4"
* by Ilya Mironov.
*/
for (n = 0; n < 256*4; n++)
arc4_randbyte();
for (n = 0; n < 768; n++)
(void)arc4_randbyte();
mtx_unlock(&arc4_mtx);
}