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util: add constant-time memcmp

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Import from vboot_reference the constant-time memcmp implementation
for safer usage in cryptography code.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=chrome-os-partner:62991
TEST=run curve25519 test

Change-Id: I9c4c61e15912c978e13b6cc002af879c8ae8f630
Reviewed-on: https://chromium-review.googlesource.com/446098
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
This commit is contained in:
Vincent Palatin
2017-02-22 10:37:39 +01:00
committed by chrome-bot
parent b8c4f23f75
commit bff020fc6b
2 changed files with 20 additions and 0 deletions
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19
common/util.c
View File

@@ -188,6 +188,25 @@ int memcmp(const void *s1, const void *s2, size_t len)
return 0;
}
/* Constant-time memory comparison */
int safe_memcmp(const void *s1, const void *s2, size_t size)
{
const uint8_t *us1 = s1;
const uint8_t *us2 = s2;
int result = 0;
if (size == 0)
return 0;
/*
* Code snippet without data-dependent branch due to Nate Lawson
* (nate@root.org) of Root Labs.
*/
while (size--)
result |= *us1++ ^ *us2++;
return result != 0;
}
void *memcpy(void *dest, const void *src, size_t len)
{

1
include/util.h
View File

@@ -66,6 +66,7 @@ int isspace(int c);
int isalpha(int c);
int isprint(int c);
int memcmp(const void *s1, const void *s2, size_t len);
int safe_memcmp(const void *s1, const void *s2, size_t len);
void *memcpy(void *dest, const void *src, size_t len);
__visible void *memset(void *dest, int c, size_t len);
void *memmove(void *dest, const void *src, size_t len);