On Mon 2016-06-13 11:48:39, Theodore Ts'o wrote:
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> ---
> drivers/char/random.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 49 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index d640865..963a6a9 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -436,7 +436,8 @@ static int crng_init = 0;
> #define crng_ready() (likely(crng_init > 0))
> static void _extract_crng(struct crng_state *crng,
> __u8 out[CHACHA20_BLOCK_SIZE]);
> -static void extract_crng(__u8 out[CHACHA20_BLOCK_SIZE]);
> +static void _crng_backtrack_protect(struct crng_state *crng,
> + __u8 tmp[CHACHA20_BLOCK_SIZE], int used);
> static void process_random_ready_list(void);
You can do u8 and u32 in the code, we know we are in kernel.
> +/*
> + * Use the leftover bytes from the CRNG block output (if there is
> + * enough) to mutate the CRNG key to provide backtracking protection.
> + */
> +static void _crng_backtrack_protect(struct crng_state *crng,
> + __u8 tmp[CHACHA20_BLOCK_SIZE], int used)
> +{
> + unsigned long flags;
> + __u32 *s, *d;
> + int i;
> +
> + used = round_up(used, sizeof(__u32));
> + if (used + CHACHA20_KEY_SIZE > CHACHA20_BLOCK_SIZE) {
> + extract_crng(tmp);
> + used = 0;
> + }
> + spin_lock_irqsave(&crng->lock, flags);
> + s = (__u32 *) &tmp[used];
> + d = &crng->state[4];
> + for (i=0; i < 8; i++)
> + *d++ ^= *s++;
> + spin_unlock_irqrestore(&crng->lock, flags);
> +}
You are basically trying to turn CRNG into one way hash function here,
right? Do you have any explanation that it has the required
properties?
Thanks,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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