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// This file was extracted from the TCG Published
// Trusted Platform Module Library
// Part 4: Supporting Routines
// Family "2.0"
// Level 00 Revision 01.16
// October 30, 2014
#include <stdlib.h>
#include <stdint.h>
#include <memory.h>
#include "TpmBuildSwitches.h"
//
//
// Local values
//
// This is the last 32-bits of hardware entropy produced. We have to check to see that two consecutive 32-
// bit values are not the same because (according to FIPS 140-2, annex C
// “If each call to a RNG produces blocks of n bits (where n > 15), the first n-bit block generated after
// power-up, initialization, or reset shall not be used, but shall be saved for comparison with the next n-
// bit block to be generated. Each subsequent generation of an n-bit block shall be compared with the
// previously generated block. The test shall fail if any two compared n-bit blocks are equal.”
//
extern uint32_t lastEntropy;
extern int firstValue;
//
//
// _plat__GetEntropy()
//
// This function is used to get available hardware entropy. In a hardware implementation of this function,
// there would be no call to the system to get entropy. If the caller does not ask for any entropy, then this is
// a startup indication and firstValue should be reset.
//
// Return Value Meaning
//
// <0 hardware failure of the entropy generator, this is sticky
// >= 0 the returned amount of entropy (bytes)
//
LIB_EXPORT int32_t
_plat__GetEntropy(
unsigned char *entropy, // output buffer
uint32_t amount // amount requested
)
{
uint32_t rndNum;
if(amount == 0)
{
firstValue = 1;
return 0;
}
// Only provide entropy 32 bits at a time to test the ability
// of the caller to deal with partial results.
rndNum = random(); //TODO(vbendeb): compare to rand_s case
if(firstValue)
firstValue = 0;
lastEntropy = rndNum;
if(amount > sizeof(rndNum))
amount = sizeof(rndNum);
memcpy(entropy, &rndNum, amount);
return (int32_t)amount;
}
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