1 /* Microsoft Reference Implementation for TPM 2.0
2 *
3 * The copyright in this software is being made available under the BSD License,
4 * included below. This software may be subject to other third party and
5 * contributor rights, including patent rights, and no such rights are granted
6 * under this license.
7 *
8 * Copyright (c) Microsoft Corporation
9 *
10 * All rights reserved.
11 *
12 * BSD License
13 *
14 * Redistribution and use in source and binary forms, with or without modification,
15 * are permitted provided that the following conditions are met:
16 *
17 * Redistributions of source code must retain the above copyright notice, this list
18 * of conditions and the following disclaimer.
19 *
20 * Redistributions in binary form must reproduce the above copyright notice, this
21 * list of conditions and the following disclaimer in the documentation and/or other
22 * materials provided with the distribution.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ""AS IS""
25 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
27 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
28 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
29 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
30 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
31 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
32 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
33 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
34 */
35
36 //** Includes
37 #include "stm32l4xx_hal.h"
38 #include <stdlib.h>
39 #include <memory.h>
40 #include "PlatformData.h"
41 #include "Platform_fp.h"
42
43 #define MIN(a,b) ((a) < (b) ? (a) : (b))
44
45 extern RNG_HandleTypeDef hrng;
46
47 //** Local values
48 // This is the last 32-bits of hardware entropy produced. We have to check to
49 // see that two consecutive 32-bit values are not the same because
50 // (according to FIPS 140-2, annex C
51 //
52 // 1. If each call to a RNG produces blocks of n bits (where n > 15), the first
53 // n-bit block generated after power-up, initialization, or reset shall not be
54 // used, but shall be saved for comparison with the next n-bit block to be
55 // generated. Each subsequent generation of an n-bit block shall be compared with
56 // the previously generated block. The test shall fail if any two compared n-bit
57 // blocks are equal.
58 extern uint32_t lastEntropy;
59
60 extern int firstValue;
61
62 //** _plat__GetEntropy()
63 // This function is used to get available hardware entropy. In a hardware
64 // implementation of this function, there would be no call to the system
65 // to get entropy.
66 // If the caller does not ask for any entropy, then this is a startup indication
67 // and 'firstValue' should be reset.
68
69 // return type: int32_t
70 // < 0 hardware failure of the entropy generator, this is sticky
71 // >= 0 the returned amount of entropy (bytes)
72 //
73 LIB_EXPORT int32_t
_plat__GetEntropy(unsigned char * entropy,uint32_t amount)74 _plat__GetEntropy(
75 unsigned char *entropy, // output buffer
76 uint32_t amount // amount requested
77 )
78 {
79 uint32_t random32bit;
80
81 if(amount == 0)
82 {
83 firstValue = 1;
84 return 0;
85 }
86
87 if(firstValue)
88 {
89 firstValue = 0;
90 }
91
92 for(uint32_t n = 0; n < amount; n += sizeof(random32bit))
93 {
94 if((HAL_RNG_GenerateRandomNumber(&hrng, &random32bit) != HAL_OK) ||
95 (~firstValue && (lastEntropy == random32bit)))
96 {
97 return -1;
98 }
99 memcpy(&entropy[n], &random32bit, MIN(sizeof(random32bit), amount - n));
100 lastEntropy = random32bit;
101 }
102
103 return (int32_t)amount;
104 }
105