Take randomness from system, as function pointer

zanebeckwith commented 6 years ago

This removes the ecdaa_prng user-space cryptographically-secure random number generator (which was just a wrapper around AMCL's csprng), in favor of taking a function-pointer from the user that gives us random numbers directly. The intention (and what is illustrated in the examples) is that this function will use the system's source of randomness (e.g. getrandom on Linux, or just /dev/urandom).

This is done for two reasons:

General cryptographic best practice currently recommends against using user-space csprngs, and instead drawing directly from system-provided sources. In our case, this is largely to avoid extra crypto code that hasn't had the same code review as the system-provided sources.
It would be nice to not have to link against libsodium in this library. Previously, we had to simply to get access to their randombytes_buf function, which is just a cross-platform wrapper around system-provided sources of randomness. Now, we suggest that randombytes_buf is a good choice, but we don't require it and instead use our own (stripped-down, fewer-platform-supporting) implementation of randombytes_buf in the examples.

Fixes #96 Also, because we no longer use randombytes_buf in our tests, and thus no longer check that the system's csprng has been properly seeded (we have a warning about this in the README), we shouldn't get the intermittent errors in travis-ci that we had before. So, this Fixes #88.

coveralls commented 6 years ago

Coverage increased (+0.0009%) to 93.329% when pulling 7945878560fb6509dab604d94b831968f8fb533d on zanebeckwith:no-userspace-csprng into 677c12a5814dba7441c8354f82f54ed6c728ac7d on xaptum:master.

zanebeckwith commented 6 years ago

@drbild I shortened the names, and moved the pool-related stuff into a separate file, under common/internal-utilities.

Let me know what you think.

drbild commented 6 years ago

Looks like the README needs the ecdaa_randomness_func_t to ecdaa_rand_func change too.

Also, should the pool stuff become ecdaa_rand_pool rather than ecdaa_randomness_pool, etc?

zanebeckwith commented 6 years ago

Rargh, good catch on the names.

Alright, now, fixed. Sorry.

xaptum / ecdaa

Take randomness from system, as function pointer #106