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Use RdSeed when available, and reduce RdRand load

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This introduces support for autodetecting and using the RdSeed instruction.

In addition:
* In SeedFast, only 64 bits of entropy are generated through RdRand (256 was relatively slow).
* In SeedStartup, 256 bits of entropy are generated, using RdSeed (preferably) or RdRand (otherwise).
This commit is contained in:
Pieter Wuille
2019-01-24 18:40:02 -08:00
parent 72bd4ab867
commit 1435fabc19
2 changed files with 137 additions and 40 deletions
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3
src/random.h
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@@ -24,7 +24,7 @@
* perform 'fast' seeding, consisting of mixing in:
* - A stack pointer (indirectly committing to calling thread and call stack)
* - A high-precision timestamp (rdtsc when available, c++ high_resolution_clock otherwise)
* - Hardware RNG (rdrand) when available.
* - 64 bits from the hardware RNG (rdrand) when available.
* These entropy sources are very fast, and only designed to protect against situations
* where a VM state restore/copy results in multiple systems with the same randomness.
* FastRandomContext on the other hand does not protect against this once created, but
@@ -48,6 +48,7 @@
*
* On first use of the RNG (regardless of what function is called first), all entropy
* sources used in the 'slow' seeder are included, but also:
* - 256 bits from the hardware RNG (rdseed or rdrand) when available.
* - (On Windows) Performance monitoring data from the OS.
* - (On Windows) Through OpenSSL, the screen contents.
*