// 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 "PlatformData.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.”

//

//

//

//          _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;

}