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arc4random(3): Reduce diff with OpenBSD.

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The main change was v1.57 by djm@:

  Randomise the rekey interval a little. Previously, the chacha20
  instance would be rekeyed every 1.6MB. This makes it happen at a
  random point somewhere in the 1-2MB range.

Reviewed by:	csprng (markm, cem)
MFC after:	2 weeks
Differential Revision: https://reviews.freebsd.org/D36088
This commit is contained in:
Xin LI 2022-08-09 17:27:54 -07:00
parent 1dfa8b73f6
commit e9a2e4d1d2
1 changed files with 8 additions and 2 deletions
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10
lib/libc/gen/arc4random.c
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@ -1,4 +1,4 @@
/* $OpenBSD: arc4random.c,v 1.55 2019/03/24 17:56:54 deraadt Exp $ */
/* $OpenBSD: arc4random.c,v 1.58 2022/07/31 13:41:45 tb Exp $ */
/*
* Copyright (c) 1996, David Mazieres <dm@uun.org>
@ -66,6 +66,8 @@ __FBSDID("$FreeBSD$");
#define BLOCKSZ 64
#define RSBUFSZ (16*BLOCKSZ)
#define REKEY_BASE (1024*1024) /* NB. should be a power of 2 */
/* Marked INHERIT_ZERO, so zero'd out in fork children. */
static struct _rs {
size_t rs_have; /* valid bytes at end of rs_buf */
@ -106,6 +108,7 @@ static void
_rs_stir(void)
{
u_char rnd[KEYSZ + IVSZ];
uint32_t rekey_fuzz = 0;
#if defined(__FreeBSD__)
bool need_init;
@ -152,7 +155,10 @@ _rs_stir(void)
rs->rs_have = 0;
memset(rsx->rs_buf, 0, sizeof(rsx->rs_buf));
rs->rs_count = 1600000;
/* rekey interval should not be predictable */
chacha_encrypt_bytes(&rsx->rs_chacha, (uint8_t *)&rekey_fuzz,
(uint8_t *)&rekey_fuzz, sizeof(rekey_fuzz));
rs->rs_count = REKEY_BASE + (rekey_fuzz % REKEY_BASE);
}
static inline void