Re: RAND_bytes() returns zero in pre-boot environment

[chris . gray]

> Issue is fixed.

So long as it's OK to generate the same "random" bytes at each power-on.

This is quite a common problem with embedded devices: even after boot it
can be hard to find entropy with which to seed the PRNG.  The "usual"
sources which are used in a PC environment (keystrokes, ethernet activity,
...) are often absent.

The best solution is always hardware. If you wire up a digital i/o in such
a way that reading it produces an unpredictable series of 0's and 1's[1]
then at least you have some genuine entropy to work with.  It doesn't have
to be ERNIE[2] to be better than nothing.

[1] Exactly how to do this is off-topic for this list. Quaerendo invenietis.
[2] For non-Brits: .

> FYI-
> As I am working on pre-boot, no OS is present. Which was resulting in no
> seeding.
> RAND_seed() has been called before using RAND_bytes().
>
> Here is the code snippet.
> static const char rnd_seed[] = "string to make the random number generator
> think it has entropy";
>  RAND_seed(rnd_seed, sizeof rnd_seed);
>
>
> On Tue, Aug 13, 2013 at 6:16 PM, baban devkate  wrote:
>
>>
>>   FYI -
>>
>> RAND_bytes(buf, bytes) receives  correct parameters as bytes=256 for
>> SHA256.
>>
>>
>> int RAND_bytes(unsigned char *buf, int num)
>> {
>> const RAND_METHOD *meth = RAND_get_rand_method();
>>  if (meth && meth->bytes)
>> {
>> Print(L"   control is here\n");/<---controll is here
>>  return meth->bytes(buf,num);
>> }
>> Print(L"   RAND_bytes fails\n");
>>
>> return(-1);
>> }
>>
>>
>> On Tue, Aug 13, 2013 at 3:35 PM, baban devkate 
>> wrote:
>>
>>> Hello,
>>>
>>> RAND_bytes() will use the proper OS-provided RNG e.g. /dev/urandom or
>>> /dev/randomon Linux and CryptGenRandom() on Windows.
>>>
>>> I want to know how it works in Pre-boot environement?
>>>
>>> In pre-boot environment, if RAND_bytes() returns zero then what does it
>>> mean?
>>>
>>> Is it because PRNG is not properly seeded? If yes, how to resolve it?
>>>
>>>
>>> ~Baban
>>>
>>
>>
>

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Re: RAND_bytes() returns zero in pre-boot environment

[baban devkate]

Issue is fixed.

FYI-
As I am working on pre-boot, no OS is present. Which was resulting in no
seeding.
RAND_seed() has been called before using RAND_bytes().

Here is the code snippet.
static const char rnd_seed[] = "string to make the random number generator
think it has entropy";
 RAND_seed(rnd_seed, sizeof rnd_seed);


On Tue, Aug 13, 2013 at 6:16 PM, baban devkate  wrote:

>
>   FYI -
>
> RAND_bytes(buf, bytes) receives  correct parameters as bytes=256 for
> SHA256.
>
>
> int RAND_bytes(unsigned char *buf, int num)
> {
> const RAND_METHOD *meth = RAND_get_rand_method();
>  if (meth && meth->bytes)
> {
> Print(L"   control is here\n");/<---controll is here
>  return meth->bytes(buf,num);
> }
> Print(L"   RAND_bytes fails\n");
>
> return(-1);
> }
>
>
> On Tue, Aug 13, 2013 at 3:35 PM, baban devkate  wrote:
>
>> Hello,
>>
>> RAND_bytes() will use the proper OS-provided RNG e.g. /dev/urandom or
>> /dev/randomon Linux and CryptGenRandom() on Windows.
>>
>> I want to know how it works in Pre-boot environement?
>>
>> In pre-boot environment, if RAND_bytes() returns zero then what does it
>> mean?
>>
>> Is it because PRNG is not properly seeded? If yes, how to resolve it?
>>
>>
>> ~Baban
>>
>
>

Re: RAND_bytes() returns zero in pre-boot environment

[baban devkate]

  FYI -

RAND_bytes(buf, bytes) receives  correct parameters as bytes=256 for SHA256.


int RAND_bytes(unsigned char *buf, int num)
{
const RAND_METHOD *meth = RAND_get_rand_method();
if (meth && meth->bytes)
{
Print(L"   control is here\n");/<---controll is here
return meth->bytes(buf,num);
}
Print(L"   RAND_bytes fails\n");

return(-1);
}


On Tue, Aug 13, 2013 at 3:35 PM, baban devkate  wrote:

> Hello,
>
> RAND_bytes() will use the proper OS-provided RNG e.g. /dev/urandom or
> /dev/randomon Linux and CryptGenRandom() on Windows.
>
> I want to know how it works in Pre-boot environement?
>
> In pre-boot environment, if RAND_bytes() returns zero then what does it
> mean?
>
> Is it because PRNG is not properly seeded? If yes, how to resolve it?
>
>
> ~Baban
>