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/** @file
BaseRng Library that uses the TimerLib to provide reasonably random numbers.
Do not use this on a production system.
Copyright (c) Microsoft Corporation.
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
#include <Base.h>
#include <Library/BaseLib.h>
#include <Library/DebugLib.h>
#include <Library/TimerLib.h>
#define DEFAULT_DELAY_TIME_IN_MICROSECONDS 10
/**
Using the TimerLib GetPerformanceCounterProperties() we delay
for enough time for the PerformanceCounter to increment.
If the return value from GetPerformanceCounterProperties (TimerLib)
is zero, this function will return 10 and attempt to assert.
**/
STATIC
UINT32
CalculateMinimumDecentDelayInMicroseconds (
VOID
)
{
UINT64 CounterHz;
// Get the counter properties
CounterHz = GetPerformanceCounterProperties (NULL, NULL);
// Make sure we won't divide by zero
if (CounterHz == 0) {
ASSERT(CounterHz != 0); // Assert so the developer knows something is wrong
return DEFAULT_DELAY_TIME_IN_MICROSECONDS;
}
// Calculate the minimum delay based on 1.5 microseconds divided by the hertz.
// We calculate the length of a cycle (1/CounterHz) and multiply it by 1.5 microseconds
// This ensures that the performance counter has increased by at least one
return (UINT32)(MAX (DivU64x64Remainder (1500000,CounterHz, NULL), 1));
}
/**
Generates a 16-bit random number.
if Rand is NULL, then ASSERT().
@param[out] Rand Buffer pointer to store the 16-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
BOOLEAN
EFIAPI
GetRandomNumber16 (
OUT UINT16 *Rand
)
{
UINT32 Index;
UINT8 *RandPtr;
UINT32 DelayInMicroSeconds;
ASSERT (Rand != NULL);
if (Rand == NULL) {
return FALSE;
}
DelayInMicroSeconds = CalculateMinimumDecentDelayInMicroseconds ();
RandPtr = (UINT8*)Rand;
// Get 2 bytes of random ish data
for (Index = 0; Index < sizeof(UINT16); Index ++) {
*RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
// Delay to give the performance counter a chance to change
MicroSecondDelay (DelayInMicroSeconds);
RandPtr++;
}
return TRUE;
}
/**
Generates a 32-bit random number.
if Rand is NULL, then ASSERT().
@param[out] Rand Buffer pointer to store the 32-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
BOOLEAN
EFIAPI
GetRandomNumber32 (
OUT UINT32 *Rand
)
{
UINT32 Index;
UINT8 *RandPtr;
UINT32 DelayInMicroSeconds;
ASSERT (Rand != NULL);
if (NULL == Rand) {
return FALSE;
}
RandPtr = (UINT8 *) Rand;
DelayInMicroSeconds = CalculateMinimumDecentDelayInMicroseconds ();
// Get 4 bytes of random ish data
for (Index = 0; Index < sizeof(UINT32); Index ++) {
*RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
// Delay to give the performance counter a chance to change
MicroSecondDelay (DelayInMicroSeconds);
RandPtr++;
}
return TRUE;
}
/**
Generates a 64-bit random number.
if Rand is NULL, then ASSERT().
@param[out] Rand Buffer pointer to store the 64-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
BOOLEAN
EFIAPI
GetRandomNumber64 (
OUT UINT64 *Rand
)
{
UINT32 Index;
UINT8 *RandPtr;
UINT32 DelayInMicroSeconds;
ASSERT (Rand != NULL);
if (NULL == Rand) {
return FALSE;
}
RandPtr = (UINT8 *)Rand;
DelayInMicroSeconds = CalculateMinimumDecentDelayInMicroseconds ();
// Get 8 bytes of random ish data
for (Index = 0; Index < sizeof(UINT64); Index ++) {
*RandPtr = (UINT8)(GetPerformanceCounter () & 0xFF);
// Delay to give the performance counter a chance to change
MicroSecondDelay (DelayInMicroSeconds);
RandPtr++;
}
return TRUE;
}
/**
Generates a 128-bit random number.
if Rand is NULL, then ASSERT().
@param[out] Rand Buffer pointer to store the 128-bit random value.
@retval TRUE Random number generated successfully.
@retval FALSE Failed to generate the random number.
**/
BOOLEAN
EFIAPI
GetRandomNumber128 (
OUT UINT64 *Rand
)
{
ASSERT (Rand != NULL);
// This should take around 80ms
// Read first 64 bits
if (!GetRandomNumber64 (Rand)) {
return FALSE;
}
// Read second 64 bits
return GetRandomNumber64 (++Rand);
}
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