Move pal_random to System.Native from CoreRT

[jkotas]

Move https://github.com/dotnet/corert/blob/master/src/Native/System.Private.CoreLib.Native/pal_random.cpp to System.Native so that it can be shared between CoreCLR and CoreRT CoreLibs

[stephentoub]

We already have:

corefx/src/Native/Unix/System.Security.Cryptography.Native/openssl.cpp

Line 1174 in fbf441a

extern "C" int32_t CryptoNative_GetRandomBytes(uint8_t* buf, int32_t num)

and

corefx/src/Native/Unix/System.Security.Cryptography.Native.Apple/pal_random.cpp

Line 10 in bffef76

extern "C" int AppleCryptoNative_GetRandomBytes(uint8_t* pBuf, uint32_t cbBuf, int32_t* pkCCStatus)

Can/should we avoid having another mechanism?
cc: @bartonjs

[jkotas]

I am not going to add dependency from low-level runtime that just needs to generate a couple of good enough random numbers to the big crypto stack. Almost the same code is in CoreCLR PAL today. This is just to improve sharing between CoreCLR and CoreRT.

[stephentoub]

Fair enough. We should just make sure we don't inadvertently start using this in places we should be using the other ones. Or alternatively if there's no reason to be using the others, just use this one. My uber point is how many different "get random bytes" functions do we actually need.

[jkotas]

@alexperovich This will let us move Unix GetRandomBytes to the shared corelib partition.

[jkotas]

I have renamed the method to SystemNative_GetNonCryptographicallySecureRandomBytes to make it clear what it does.

[stephentoub]

Great. Thanks.

[jkotas]

@dotnet-bot test Innerloop OSX Debug Build and Test please