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
_plat__GetEntropy(unsigned char * entropy,uint32_t amount)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