1 // This file was extracted from the TCG Published 2 // Trusted Platform Module Library 3 // Part 4: Supporting Routines 4 // Family "2.0" 5 // Level 00 Revision 01.16 6 // October 30, 2014 7 8 #include <stdlib.h> 9 #include <stdint.h> 10 #include <memory.h> 11 #include "TpmBuildSwitches.h" 12 // 13 // 14 // Local values 15 // 16 // This is the last 32-bits of hardware entropy produced. We have to check to see that two consecutive 32- 17 // bit values are not the same because (according to FIPS 140-2, annex C 18 // If each call to a RNG produces blocks of n bits (where n > 15), the first n-bit block generated after 19 // power-up, initialization, or reset shall not be used, but shall be saved for comparison with the next n- 20 // bit block to be generated. Each subsequent generation of an n-bit block shall be compared with the 21 // previously generated block. The test shall fail if any two compared n-bit blocks are equal. 22 // 23 extern uint32_t lastEntropy; 24 extern int firstValue; 25 // 26 // 27 // _plat__GetEntropy() 28 // 29 // This function is used to get available hardware entropy. In a hardware implementation of this function, 30 // there would be no call to the system to get entropy. If the caller does not ask for any entropy, then this is 31 // a startup indication and firstValue should be reset. 32 // 33 // Return Value Meaning 34 // 35 // <0 hardware failure of the entropy generator, this is sticky 36 // >= 0 the returned amount of entropy (bytes) 37 // 38 LIB_EXPORT int32_t 39 _plat__GetEntropy( 40 unsigned char *entropy, // output buffer 41 uint32_t amount // amount requested 42 ) 43 { 44 uint32_t rndNum; 45 46 if(amount == 0) 47 { 48 firstValue = 1; 49 return 0; 50 } 51 // Only provide entropy 32 bits at a time to test the ability 52 // of the caller to deal with partial results. 53 rndNum = random(); //TODO(vbendeb): compare to rand_s case 54 if(firstValue) 55 firstValue = 0; 56 57 lastEntropy = rndNum; 58 if(amount > sizeof(rndNum)) 59 amount = sizeof(rndNum); 60 memcpy(entropy, &rndNum, amount); 61 62 return (int32_t)amount; 63 } 64
