[Olsr-dev] /dev/random can block forever - Re: [PATCH v1 1/1] main: improve random number generator seed

[Ferry Huberts]

I'm fine with /dev/urandom only.

On 25/03/13 03:22, Henning Rogge wrote:
> What do you think Ferry,
>
> just move to /dev/urandom? the rand() function is not photographically
> safe anyways, so we don't need to overdo it at the initialization.
>
> Henning Rogge
>
> On Sat, Mar 23, 2013 at 12:19 AM, Björn Lichtblau
> <(spam-protected)> wrote:
>> Hi,
>>
>> /dev/random can block forever if not enough entropy is available. It does on
>> my systems, the problem is described here in detail:
>> http://www.usn-it.de/index.php/2009/02/20/oracle-11g-jdbc-driver-hangs-blocked-by-devrandom-entropy-pool-empty/
>>
>> Works fine for me when using /dev/urandom, what should be the default imho,
>> it never blocks and pseudo random numbers should be enough if it is just
>> used for the jitter.
>>
>>  From "man 4 random":
>>
>>         When read, the /dev/random device will only return random bytes
>> within  the  estimated
>>         number  of  bits of noise in the entropy pool.  /dev/random should be
>> suitable for uses
>>         that need very high quality randomness such as one-time pad or  key
>> generation.   When
>>         the  entropy pool is empty, reads from /dev/random will block until
>> additional environ‐
>>         mental noise is gathered.
>>
>>         A read from the /dev/urandom device will not block waiting  for  more
>> entropy.   As  a
>>         result, if there is not sufficient entropy in the entropy pool, the
>> returned values are
>>         theoretically vulnerable to a cryptographic  attack  on  the
>> algorithms  used  by  the
>>         driver.   Knowledge of how to do this is not available in the current
>> unclassified lit‐
>>         erature, but it is theoretically possible that such an attack may
>> exist.  If this is  a
>>         concern in your application, use /dev/random instead.
>>
>>     Usage
>>         If you are unsure about whether you should use /dev/random or
>> /dev/urandom, then proba‐
>>         bly you want to use the latter.  As a general rule, /dev/urandom
>> should  be  used  for
>>         everything except long-lived GPG/SSL/SSH keys.
>>
>>
>> bye, Björn
>>
>>
>>
>>
>> On 10.11.2012 11:50, Ferry Huberts wrote:
>>
>> From: Ferry Huberts <(spam-protected)>
>>
>> Make it much more random when /dev/random or /dev/urandom is
>> available.
>>
>> Signed-off-by: Ferry Huberts <(spam-protected)>
>> ---
>>   src/main.c | 24 +++++++++++++++++++++++-
>>   1 file changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/main.c b/src/main.c
>> index ae38439..382c5dc 100644
>> --- a/src/main.c
>> +++ b/src/main.c
>> @@ -230,6 +230,28 @@ olsrmain_load_config(char *file) {
>>     return 0;
>>   }
>>
>> +static void initRandom(void) {
>> +  unsigned int seed = (unsigned int)time(NULL);
>> +
>> +#ifndef _WIN32
>> +  int randomFile;
>> +
>> +  randomFile = open("/dev/random", O_RDONLY);
>> +  if (randomFile == -1) {
>> +    randomFile = open("/dev/urandom", O_RDONLY);
>> +  }
>> +
>> +  if (randomFile != -1) {
>> +    if (read(randomFile, &seed, sizeof(seed)) != sizeof(seed)) {
>> +      ; /* to fix an 'unused result' compiler warning */
>> +    }
>> +    close(randomFile);
>> +  }
>> +#endif /* _WIN32 */
>> +
>> +  srandom(seed);
>> +}
>> +
>>   /**
>>    * Main entrypoint
>>    */
>> @@ -297,7 +319,7 @@ int main(int argc, char *argv[]) {
>>     olsr_openlog("olsrd");
>>
>>     /* setup random seed */
>> -  srandom(time(NULL));
>> +  initRandom();
>>
>>     /* Init widely used statics */
>>     memset(&all_zero, 0, sizeof(union olsr_ip_addr));
>>
>>
>>
>> --
>> Olsr-dev mailing list
>> (spam-protected)
>> https://lists.olsr.org/mailman/listinfo/olsr-dev
>
>
>

-- 
Ferry Huberts