c - OpenSSL random - using ENGINE API to set random, what is the right way to do it? -


in openssl, using engine taking use of hardware, i'm trying make sure rand_bytes use engine , hardware. came across 2 functions:

engine_set_default_rand(engine*) rand_set_rand_engine(engine*)

seemingly - same. why there 2 of them? 1 right way go?

i've further tested if set functions work disconnecting hardware , performing init, rand_bytes. using first function (engine_set_default_rand) suceeded - software implementation used (why?). when changed second failed on set rand_set_rand_engine function call (which great).

according to: https://www.openssl.org/docs/crypto/engine.html#application_requirements engine_set_default_(engine)* way go, e.g.:

engine_set_default_rand(myptrengine);

which worked, causing engine implementation used. i've tested modifying custom engine code, injecting simple printfs(...) indicate flow (had problems debugging).

the other call:

rand_set_rand_engine(myptrengine);

resulted in same (i not know internal differences).

the problem caused me ask, possibility of fallback-to-software mechanism. hardware disconnected , engine using set, random functions seemingly worked. therefore did not know whether engine_set_default_rand worked. after examining engine's code, however, turned out had fallback mechanism. that's why always worked.


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