Module Name: src
Committed By: riastradh
Date: Fri May 13 09:40:25 UTC 2022
Modified Files:
src/sys/kern: subr_cprng.c
Log Message:
cprng(9): Fix accidental 4x seed size.
With SHA-256, NIST Hash_DRBG takes an preferred 440-bit/55-byte seed.
It's a weird number, and I'm not sure where it comes from (a quick
skim of SP800-90A doesn't turn anything up), but it's certainly
sufficient (256-bit/32-byte seed is almost certainly enough) so it's
not a problem to use something larger; Hash_DRBG can absorb seeds of
arbitrary lengths and larger seeds can't really hurt security (with
minor caveats like HMAC RO quirks that don't apply here).
Except -- owing to a typo, we actually used a 1760-bit/220-byte seed,
because I wrote `uint32_t seed[...]' instead of `uint8_t seed[...]'.
Again: not a problem to use a seed larger than needed. But let's
draw no more than we need out of the entropy pool!
Verified with CTASSERT(sizeof(seed) == 55). (Assertion omitted from
this commit because we might swap out Hash_DRBG for something else
with a different seed size like 32 bytes.)
To generate a diff of this commit:
cvs rdiff -u -r1.42 -r1.43 src/sys/kern/subr_cprng.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/subr_cprng.c
diff -u src/sys/kern/subr_cprng.c:1.42 src/sys/kern/subr_cprng.c:1.43
--- src/sys/kern/subr_cprng.c:1.42 Wed Mar 16 23:56:33 2022
+++ src/sys/kern/subr_cprng.c Fri May 13 09:40:25 2022
@@ -1,4 +1,4 @@
-/* $NetBSD: subr_cprng.c,v 1.42 2022/03/16 23:56:33 riastradh Exp $ */
+/* $NetBSD: subr_cprng.c,v 1.43 2022/05/13 09:40:25 riastradh Exp $ */
/*-
* Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -52,7 +52,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: subr_cprng.c,v 1.42 2022/03/16 23:56:33 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: subr_cprng.c,v 1.43 2022/05/13 09:40:25 riastradh Exp $");
#include <sys/param.h>
#include <sys/types.h>
@@ -268,7 +268,7 @@ cprng_fini_cpu(void *ptr, void *cookie,
size_t
cprng_strong(struct cprng_strong *cprng, void *buf, size_t len, int flags)
{
- uint32_t seed[NIST_HASH_DRBG_SEEDLEN_BYTES];
+ uint8_t seed[NIST_HASH_DRBG_SEEDLEN_BYTES];
struct cprng_cpu *cc;
unsigned epoch;
int s;
