Re: [PATCH v2] memcmp.3: Recast security caveat

[Alejandro Colomar <alx@kernel.org>]

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Hi Branden,

On 2023-07-30 17:31, G. Branden Robinson wrote:
> Use terminology more carefully.
> 
> * Refer to the info sec property of confidentiality instead of saying,
>   vaguely, "security-critical".
>     https://informationsecurity.wustl.edu/items/\
>     confidentiality-integrity-and-availability-the-cia-triad/
> * Try not to confuse anyone who's studied the analysis of algorithms:
>   don't say "constant time" when "deterministic time" is meant.  The
>   time to perform the memory comparison remains linear (O(n)), not
>   constant (O(1)).
> * Tighten wording.

I prefer 2 spaces between the bullet and the list contents.  See
man-pages(7).  Anyway, I accepted it this time.  :)


> 
> Signed-off-by: G. Branden Robinson <g.branden.robinson@gmail.com>

You need to quote your name with '"' due to the '.'.  I've found
some software has issues with it.  git-send-email(1) is one of them
(due to the perl library it uses).

Anyway, patch applied.  Thanks!

Cheers,
Alex

> ---
>  man3/memcmp.3 | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/man3/memcmp.3 b/man3/memcmp.3
> index 9a2aad353..67ebe392e 100644
> --- a/man3/memcmp.3
> +++ b/man3/memcmp.3
> @@ -67,9 +67,17 @@ .SH HISTORY
>  .SH CAVEATS
>  Do not use
>  .BR memcmp ()
> -to compare security critical data, such as cryptographic secrets,
> -because the required CPU time depends on the number of equal bytes.
> -Instead, a function that performs comparisons in constant time is required.
> +to compare confidential data,
> +such as cryptographic secrets,
> +because the CPU time required for the comparison
> +depends on the contents of the addresses compared,
> +this function is subject to timing-based side-channel attacks.
> +In such cases,
> +a function that performs comparisons in deterministic time,
> +depending only on
> +.I n
> +(the quantity of bytes compared)
> +is required.
>  Some operating systems provide such a function (e.g., NetBSD's
>  .BR consttime_memequal ()),
>  but no such function is specified in POSIX.

-- 
<http://www.alejandro-colomar.es/>
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