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