[openssl-dev] Plea for a new public OpenSSL RNG API

[Blumenthal, Uri - 0553 - MITLL]

I like this PR. Thank you!

> On Sep 3, 2017, at 17:53, Dr. Matthias St. Pierre <Matthias.St.Pierre at ncp-e.com> wrote:
> 
>> 
>> The 'RAND_add()/RAND_bytes()' pattern is broken
>> ===============================================
>> 
>> In OpenSSL, the classical way for the RNG consumer to add his own randomness is to call 'RAND_add()' before
>> calling 'RAND_bytes()'. If the new 'RAND_OpenSSL()' method (the "compatibility layer" hiding the public
>> RAND_DRBG instance)  is the default, then this does not work as expected anymore:
>> 
>> The reason is that a call to 'RAND_add()' adds the provided randomness only to a global buffer
>> ('rand_bytes'), from which it will be pulled during the next reseed. But no reseed is triggered. So the next
>> RAND_bytes() call will be unaffected from the RAND_add(), which is not what the consumer expected. (The same
>> holds for 'RAND_seed()', since 'drbg_seed()' only calls into 'drbg_add()')
>> 
>> Reseeding of DRBGs occurs only at the following occasions:
>> 
>> * immediately after a 'fork()' (new)
>> * if the 'reseed_counter' exceeds the 'reseed_interval'
>> * if 'RAND_DRBG_generate()' is called requesting 'prediction_resistance'
>> * 'RAND_DRBG_reseed()' is called explicitely
>> 
>> *Note:* Currently it looks like the situation is even worse: if 'RAND_add()' is called multiple times before
>> a reseed occurs, then the result of the previous call is overwritten.
> 
> 
> I just posted GitHub PR #4328 related to this issue
> 
> 	[openssl/openssl] WIP: Fix the RAND_add() reseeding issue (#4328)
> 
> 
> Matthias St. Pierre