platform-entropy.hh

#pragma once
#include <interrupt.h>
#include <platform/concepts/entropy.h>
 
DECLARE_AND_DEFINE_INTERRUPT_CAPABILITY(revokerInterruptEntropy,
                                        InterruptName::EthernetReceiveInterrupt,
                                        true,
                                        false)
 
/**
 * A simple entropy source.  This wraps a few weak entropy sources to seed a
 * PRNG.  It is absolutely not secure and should not be used for anything that
 * depends on cryptographically secure random numbers!  Unfortunately, there is
 * nothing on the Arty A7 instantiation of CHERIoT SAFE that can be used as a
 * secure entropy source.
 */
struct EntropySource : public TrivialInsecureEntropySource
{
    /// Constructor, tries to generate an independent sequence of random numbers
    EntropySource()
    {
        reseed();
    }
 
    /// Reseed the PRNG
    void reseed()
    {
        uint32_t interrupts =
          *interrupt_futex_get(STATIC_SEALED_VALUE(revokerInterruptEntropy));
        TrivialInsecureEntropySource::reseed(interrupts);
    }
};
 
static_assert(IsEntropySource<EntropySource>,
              "EntropySource must be an entropy source");