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870 lines
26 KiB
870 lines
26 KiB
/* |
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* Non-physical true random number generator based on timing jitter -- |
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* Jitter RNG standalone code. |
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* |
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* Copyright Stephan Mueller <[email protected]>, 2015 - 2020 |
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* |
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* Design |
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* ====== |
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* |
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* See https://www.chronox.de/jent.html |
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* |
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* License |
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* ======= |
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* |
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* Redistribution and use in source and binary forms, with or without |
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* modification, are permitted provided that the following conditions |
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* are met: |
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* 1. Redistributions of source code must retain the above copyright |
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* notice, and the entire permission notice in its entirety, |
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* including the disclaimer of warranties. |
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* 2. Redistributions in binary form must reproduce the above copyright |
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* notice, this list of conditions and the following disclaimer in the |
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* documentation and/or other materials provided with the distribution. |
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* 3. The name of the author may not be used to endorse or promote |
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* products derived from this software without specific prior |
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* written permission. |
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* |
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* ALTERNATIVELY, this product may be distributed under the terms of |
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* the GNU General Public License, in which case the provisions of the GPL2 are |
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* required INSTEAD OF the above restrictions. (This clause is |
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* necessary due to a potential bad interaction between the GPL and |
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* the restrictions contained in a BSD-style copyright.) |
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* |
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED |
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* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF |
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* WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE |
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT |
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* OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR |
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* BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF |
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE |
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* USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH |
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* DAMAGE. |
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*/ |
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|
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/* |
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* This Jitterentropy RNG is based on the jitterentropy library |
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* version 2.2.0 provided at https://www.chronox.de/jent.html |
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*/ |
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#ifdef __OPTIMIZE__ |
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#error "The CPU Jitter random number generator must not be compiled with optimizations. See documentation. Use the compiler switch -O0 for compiling jitterentropy.c." |
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#endif |
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typedef unsigned long long __u64; |
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typedef long long __s64; |
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typedef unsigned int __u32; |
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#define NULL ((void *) 0) |
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|
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/* The entropy pool */ |
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struct rand_data { |
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/* all data values that are vital to maintain the security |
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* of the RNG are marked as SENSITIVE. A user must not |
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* access that information while the RNG executes its loops to |
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* calculate the next random value. */ |
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__u64 data; /* SENSITIVE Actual random number */ |
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__u64 old_data; /* SENSITIVE Previous random number */ |
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__u64 prev_time; /* SENSITIVE Previous time stamp */ |
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#define DATA_SIZE_BITS ((sizeof(__u64)) * 8) |
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__u64 last_delta; /* SENSITIVE stuck test */ |
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__s64 last_delta2; /* SENSITIVE stuck test */ |
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unsigned int osr; /* Oversample rate */ |
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#define JENT_MEMORY_BLOCKS 64 |
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#define JENT_MEMORY_BLOCKSIZE 32 |
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#define JENT_MEMORY_ACCESSLOOPS 128 |
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#define JENT_MEMORY_SIZE (JENT_MEMORY_BLOCKS*JENT_MEMORY_BLOCKSIZE) |
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unsigned char *mem; /* Memory access location with size of |
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* memblocks * memblocksize */ |
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unsigned int memlocation; /* Pointer to byte in *mem */ |
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unsigned int memblocks; /* Number of memory blocks in *mem */ |
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unsigned int memblocksize; /* Size of one memory block in bytes */ |
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unsigned int memaccessloops; /* Number of memory accesses per random |
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* bit generation */ |
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/* Repetition Count Test */ |
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int rct_count; /* Number of stuck values */ |
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/* Adaptive Proportion Test for a significance level of 2^-30 */ |
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#define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */ |
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#define JENT_APT_WINDOW_SIZE 512 /* Data window size */ |
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/* LSB of time stamp to process */ |
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#define JENT_APT_LSB 16 |
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#define JENT_APT_WORD_MASK (JENT_APT_LSB - 1) |
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unsigned int apt_observations; /* Number of collected observations */ |
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unsigned int apt_count; /* APT counter */ |
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unsigned int apt_base; /* APT base reference */ |
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unsigned int apt_base_set:1; /* APT base reference set? */ |
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|
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unsigned int health_failure:1; /* Permanent health failure */ |
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}; |
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|
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/* Flags that can be used to initialize the RNG */ |
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#define JENT_DISABLE_MEMORY_ACCESS (1<<2) /* Disable memory access for more |
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* entropy, saves MEMORY_SIZE RAM for |
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* entropy collector */ |
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|
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/* -- error codes for init function -- */ |
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#define JENT_ENOTIME 1 /* Timer service not available */ |
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#define JENT_ECOARSETIME 2 /* Timer too coarse for RNG */ |
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#define JENT_ENOMONOTONIC 3 /* Timer is not monotonic increasing */ |
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#define JENT_EVARVAR 5 /* Timer does not produce variations of |
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* variations (2nd derivation of time is |
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* zero). */ |
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#define JENT_ESTUCK 8 /* Too many stuck results during init. */ |
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#define JENT_EHEALTH 9 /* Health test failed during initialization */ |
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#define JENT_ERCT 10 /* RCT failed during initialization */ |
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/* |
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* The output n bits can receive more than n bits of min entropy, of course, |
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* but the fixed output of the conditioning function can only asymptotically |
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* approach the output size bits of min entropy, not attain that bound. Random |
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* maps will tend to have output collisions, which reduces the creditable |
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* output entropy (that is what SP 800-90B Section 3.1.5.1.2 attempts to bound). |
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* |
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* The value "64" is justified in Appendix A.4 of the current 90C draft, |
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* and aligns with NIST's in "epsilon" definition in this document, which is |
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* that a string can be considered "full entropy" if you can bound the min |
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* entropy in each bit of output to at least 1-epsilon, where epsilon is |
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* required to be <= 2^(-32). |
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*/ |
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#define JENT_ENTROPY_SAFETY_FACTOR 64 |
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#include <linux/fips.h> |
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#include "jitterentropy.h" |
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/*************************************************************************** |
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* Adaptive Proportion Test |
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* |
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* This test complies with SP800-90B section 4.4.2. |
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***************************************************************************/ |
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/* |
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* Reset the APT counter |
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* |
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* @ec [in] Reference to entropy collector |
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*/ |
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static void jent_apt_reset(struct rand_data *ec, unsigned int delta_masked) |
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{ |
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/* Reset APT counter */ |
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ec->apt_count = 0; |
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ec->apt_base = delta_masked; |
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ec->apt_observations = 0; |
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} |
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/* |
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* Insert a new entropy event into APT |
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* |
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* @ec [in] Reference to entropy collector |
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* @delta_masked [in] Masked time delta to process |
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*/ |
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static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked) |
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{ |
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/* Initialize the base reference */ |
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if (!ec->apt_base_set) { |
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ec->apt_base = delta_masked; |
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ec->apt_base_set = 1; |
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return; |
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} |
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if (delta_masked == ec->apt_base) { |
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ec->apt_count++; |
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if (ec->apt_count >= JENT_APT_CUTOFF) |
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ec->health_failure = 1; |
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} |
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ec->apt_observations++; |
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if (ec->apt_observations >= JENT_APT_WINDOW_SIZE) |
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jent_apt_reset(ec, delta_masked); |
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} |
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/*************************************************************************** |
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* Stuck Test and its use as Repetition Count Test |
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* |
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* The Jitter RNG uses an enhanced version of the Repetition Count Test |
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* (RCT) specified in SP800-90B section 4.4.1. Instead of counting identical |
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* back-to-back values, the input to the RCT is the counting of the stuck |
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* values during the generation of one Jitter RNG output block. |
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* |
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* The RCT is applied with an alpha of 2^{-30} compliant to FIPS 140-2 IG 9.8. |
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* |
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* During the counting operation, the Jitter RNG always calculates the RCT |
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* cut-off value of C. If that value exceeds the allowed cut-off value, |
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* the Jitter RNG output block will be calculated completely but discarded at |
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* the end. The caller of the Jitter RNG is informed with an error code. |
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***************************************************************************/ |
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/* |
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* Repetition Count Test as defined in SP800-90B section 4.4.1 |
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* |
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* @ec [in] Reference to entropy collector |
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* @stuck [in] Indicator whether the value is stuck |
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*/ |
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static void jent_rct_insert(struct rand_data *ec, int stuck) |
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{ |
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/* |
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* If we have a count less than zero, a previous RCT round identified |
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* a failure. We will not overwrite it. |
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*/ |
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if (ec->rct_count < 0) |
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return; |
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if (stuck) { |
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ec->rct_count++; |
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/* |
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* The cutoff value is based on the following consideration: |
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* alpha = 2^-30 as recommended in FIPS 140-2 IG 9.8. |
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* In addition, we require an entropy value H of 1/OSR as this |
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* is the minimum entropy required to provide full entropy. |
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* Note, we collect 64 * OSR deltas for inserting them into |
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* the entropy pool which should then have (close to) 64 bits |
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* of entropy. |
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* |
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* Note, ec->rct_count (which equals to value B in the pseudo |
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* code of SP800-90B section 4.4.1) starts with zero. Hence |
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* we need to subtract one from the cutoff value as calculated |
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* following SP800-90B. |
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*/ |
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if ((unsigned int)ec->rct_count >= (31 * ec->osr)) { |
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ec->rct_count = -1; |
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ec->health_failure = 1; |
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} |
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} else { |
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ec->rct_count = 0; |
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} |
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} |
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/* |
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* Is there an RCT health test failure? |
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* |
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* @ec [in] Reference to entropy collector |
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* |
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* @return |
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* 0 No health test failure |
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* 1 Permanent health test failure |
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*/ |
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static int jent_rct_failure(struct rand_data *ec) |
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{ |
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if (ec->rct_count < 0) |
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return 1; |
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return 0; |
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} |
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static inline __u64 jent_delta(__u64 prev, __u64 next) |
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{ |
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#define JENT_UINT64_MAX (__u64)(~((__u64) 0)) |
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return (prev < next) ? (next - prev) : |
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(JENT_UINT64_MAX - prev + 1 + next); |
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} |
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/* |
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* Stuck test by checking the: |
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* 1st derivative of the jitter measurement (time delta) |
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* 2nd derivative of the jitter measurement (delta of time deltas) |
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* 3rd derivative of the jitter measurement (delta of delta of time deltas) |
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* |
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* All values must always be non-zero. |
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* |
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* @ec [in] Reference to entropy collector |
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* @current_delta [in] Jitter time delta |
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* |
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* @return |
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* 0 jitter measurement not stuck (good bit) |
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* 1 jitter measurement stuck (reject bit) |
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*/ |
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static int jent_stuck(struct rand_data *ec, __u64 current_delta) |
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{ |
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__u64 delta2 = jent_delta(ec->last_delta, current_delta); |
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__u64 delta3 = jent_delta(ec->last_delta2, delta2); |
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ec->last_delta = current_delta; |
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ec->last_delta2 = delta2; |
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/* |
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* Insert the result of the comparison of two back-to-back time |
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* deltas. |
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*/ |
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jent_apt_insert(ec, current_delta); |
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if (!current_delta || !delta2 || !delta3) { |
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/* RCT with a stuck bit */ |
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jent_rct_insert(ec, 1); |
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return 1; |
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} |
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/* RCT with a non-stuck bit */ |
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jent_rct_insert(ec, 0); |
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return 0; |
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} |
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/* |
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* Report any health test failures |
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* |
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* @ec [in] Reference to entropy collector |
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* |
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* @return |
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* 0 No health test failure |
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* 1 Permanent health test failure |
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*/ |
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static int jent_health_failure(struct rand_data *ec) |
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{ |
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return ec->health_failure; |
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} |
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/*************************************************************************** |
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* Noise sources |
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***************************************************************************/ |
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/* |
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* Update of the loop count used for the next round of |
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* an entropy collection. |
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* |
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* Input: |
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* @ec entropy collector struct -- may be NULL |
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* @bits is the number of low bits of the timer to consider |
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* @min is the number of bits we shift the timer value to the right at |
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* the end to make sure we have a guaranteed minimum value |
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* |
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* @return Newly calculated loop counter |
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*/ |
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static __u64 jent_loop_shuffle(struct rand_data *ec, |
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unsigned int bits, unsigned int min) |
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{ |
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__u64 time = 0; |
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__u64 shuffle = 0; |
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unsigned int i = 0; |
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unsigned int mask = (1<<bits) - 1; |
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jent_get_nstime(&time); |
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/* |
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* Mix the current state of the random number into the shuffle |
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* calculation to balance that shuffle a bit more. |
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*/ |
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if (ec) |
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time ^= ec->data; |
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/* |
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* We fold the time value as much as possible to ensure that as many |
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* bits of the time stamp are included as possible. |
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*/ |
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for (i = 0; ((DATA_SIZE_BITS + bits - 1) / bits) > i; i++) { |
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shuffle ^= time & mask; |
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time = time >> bits; |
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} |
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/* |
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* We add a lower boundary value to ensure we have a minimum |
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* RNG loop count. |
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*/ |
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return (shuffle + (1<<min)); |
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} |
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/* |
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* CPU Jitter noise source -- this is the noise source based on the CPU |
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* execution time jitter |
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* |
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* This function injects the individual bits of the time value into the |
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* entropy pool using an LFSR. |
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* |
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* The code is deliberately inefficient with respect to the bit shifting |
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* and shall stay that way. This function is the root cause why the code |
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* shall be compiled without optimization. This function not only acts as |
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* folding operation, but this function's execution is used to measure |
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* the CPU execution time jitter. Any change to the loop in this function |
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* implies that careful retesting must be done. |
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* |
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* @ec [in] entropy collector struct |
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* @time [in] time stamp to be injected |
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* @loop_cnt [in] if a value not equal to 0 is set, use the given value as |
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* number of loops to perform the folding |
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* @stuck [in] Is the time stamp identified as stuck? |
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* |
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* Output: |
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* updated ec->data |
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* |
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* @return Number of loops the folding operation is performed |
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*/ |
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static void jent_lfsr_time(struct rand_data *ec, __u64 time, __u64 loop_cnt, |
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int stuck) |
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{ |
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unsigned int i; |
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__u64 j = 0; |
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__u64 new = 0; |
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#define MAX_FOLD_LOOP_BIT 4 |
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#define MIN_FOLD_LOOP_BIT 0 |
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__u64 fold_loop_cnt = |
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jent_loop_shuffle(ec, MAX_FOLD_LOOP_BIT, MIN_FOLD_LOOP_BIT); |
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|
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/* |
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* testing purposes -- allow test app to set the counter, not |
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* needed during runtime |
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*/ |
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if (loop_cnt) |
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fold_loop_cnt = loop_cnt; |
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for (j = 0; j < fold_loop_cnt; j++) { |
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new = ec->data; |
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for (i = 1; (DATA_SIZE_BITS) >= i; i++) { |
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__u64 tmp = time << (DATA_SIZE_BITS - i); |
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|
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tmp = tmp >> (DATA_SIZE_BITS - 1); |
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|
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/* |
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* Fibonacci LSFR with polynomial of |
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* x^64 + x^61 + x^56 + x^31 + x^28 + x^23 + 1 which is |
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* primitive according to |
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* http://poincare.matf.bg.ac.rs/~ezivkovm/publications/primpol1.pdf |
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* (the shift values are the polynomial values minus one |
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* due to counting bits from 0 to 63). As the current |
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* position is always the LSB, the polynomial only needs |
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* to shift data in from the left without wrap. |
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*/ |
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tmp ^= ((new >> 63) & 1); |
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tmp ^= ((new >> 60) & 1); |
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tmp ^= ((new >> 55) & 1); |
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tmp ^= ((new >> 30) & 1); |
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tmp ^= ((new >> 27) & 1); |
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tmp ^= ((new >> 22) & 1); |
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new <<= 1; |
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new ^= tmp; |
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} |
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} |
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/* |
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* If the time stamp is stuck, do not finally insert the value into |
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* the entropy pool. Although this operation should not do any harm |
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* even when the time stamp has no entropy, SP800-90B requires that |
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* any conditioning operation (SP800-90B considers the LFSR to be a |
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* conditioning operation) to have an identical amount of input |
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* data according to section 3.1.5. |
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*/ |
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if (!stuck) |
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ec->data = new; |
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} |
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|
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/* |
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* Memory Access noise source -- this is a noise source based on variations in |
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* memory access times |
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* |
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* This function performs memory accesses which will add to the timing |
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* variations due to an unknown amount of CPU wait states that need to be |
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* added when accessing memory. The memory size should be larger than the L1 |
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* caches as outlined in the documentation and the associated testing. |
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* |
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* The L1 cache has a very high bandwidth, albeit its access rate is usually |
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* slower than accessing CPU registers. Therefore, L1 accesses only add minimal |
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* variations as the CPU has hardly to wait. Starting with L2, significant |
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* variations are added because L2 typically does not belong to the CPU any more |
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* and therefore a wider range of CPU wait states is necessary for accesses. |
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* L3 and real memory accesses have even a wider range of wait states. However, |
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* to reliably access either L3 or memory, the ec->mem memory must be quite |
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* large which is usually not desirable. |
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* |
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* @ec [in] Reference to the entropy collector with the memory access data -- if |
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* the reference to the memory block to be accessed is NULL, this noise |
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* source is disabled |
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* @loop_cnt [in] if a value not equal to 0 is set, use the given value |
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* number of loops to perform the LFSR |
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*/ |
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static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt) |
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{ |
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unsigned int wrap = 0; |
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__u64 i = 0; |
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#define MAX_ACC_LOOP_BIT 7 |
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#define MIN_ACC_LOOP_BIT 0 |
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__u64 acc_loop_cnt = |
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jent_loop_shuffle(ec, MAX_ACC_LOOP_BIT, MIN_ACC_LOOP_BIT); |
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|
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if (NULL == ec || NULL == ec->mem) |
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return; |
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wrap = ec->memblocksize * ec->memblocks; |
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|
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/* |
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* testing purposes -- allow test app to set the counter, not |
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* needed during runtime |
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*/ |
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if (loop_cnt) |
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acc_loop_cnt = loop_cnt; |
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|
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for (i = 0; i < (ec->memaccessloops + acc_loop_cnt); i++) { |
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unsigned char *tmpval = ec->mem + ec->memlocation; |
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/* |
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* memory access: just add 1 to one byte, |
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* wrap at 255 -- memory access implies read |
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* from and write to memory location |
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*/ |
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*tmpval = (*tmpval + 1) & 0xff; |
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/* |
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* Addition of memblocksize - 1 to pointer |
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* with wrap around logic to ensure that every |
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* memory location is hit evenly |
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*/ |
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ec->memlocation = ec->memlocation + ec->memblocksize - 1; |
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ec->memlocation = ec->memlocation % wrap; |
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} |
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} |
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|
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/*************************************************************************** |
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* Start of entropy processing logic |
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***************************************************************************/ |
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/* |
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* This is the heart of the entropy generation: calculate time deltas and |
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* use the CPU jitter in the time deltas. The jitter is injected into the |
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* entropy pool. |
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* |
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* WARNING: ensure that ->prev_time is primed before using the output |
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* of this function! This can be done by calling this function |
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* and not using its result. |
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* |
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* @ec [in] Reference to entropy collector |
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* |
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* @return result of stuck test |
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*/ |
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static int jent_measure_jitter(struct rand_data *ec) |
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{ |
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__u64 time = 0; |
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__u64 current_delta = 0; |
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int stuck; |
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|
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/* Invoke one noise source before time measurement to add variations */ |
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jent_memaccess(ec, 0); |
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|
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/* |
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* Get time stamp and calculate time delta to previous |
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* invocation to measure the timing variations |
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*/ |
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jent_get_nstime(&time); |
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current_delta = jent_delta(ec->prev_time, time); |
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ec->prev_time = time; |
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|
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/* Check whether we have a stuck measurement. */ |
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stuck = jent_stuck(ec, current_delta); |
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|
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/* Now call the next noise sources which also injects the data */ |
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jent_lfsr_time(ec, current_delta, 0, stuck); |
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|
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return stuck; |
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} |
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|
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/* |
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* Generator of one 64 bit random number |
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* Function fills rand_data->data |
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* |
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* @ec [in] Reference to entropy collector |
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*/ |
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static void jent_gen_entropy(struct rand_data *ec) |
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{ |
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unsigned int k = 0, safety_factor = 0; |
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|
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if (fips_enabled) |
|
safety_factor = JENT_ENTROPY_SAFETY_FACTOR; |
|
|
|
/* priming of the ->prev_time value */ |
|
jent_measure_jitter(ec); |
|
|
|
while (!jent_health_failure(ec)) { |
|
/* If a stuck measurement is received, repeat measurement */ |
|
if (jent_measure_jitter(ec)) |
|
continue; |
|
|
|
/* |
|
* We multiply the loop value with ->osr to obtain the |
|
* oversampling rate requested by the caller |
|
*/ |
|
if (++k >= ((DATA_SIZE_BITS + safety_factor) * ec->osr)) |
|
break; |
|
} |
|
} |
|
|
|
/* |
|
* Entry function: Obtain entropy for the caller. |
|
* |
|
* This function invokes the entropy gathering logic as often to generate |
|
* as many bytes as requested by the caller. The entropy gathering logic |
|
* creates 64 bit per invocation. |
|
* |
|
* This function truncates the last 64 bit entropy value output to the exact |
|
* size specified by the caller. |
|
* |
|
* @ec [in] Reference to entropy collector |
|
* @data [in] pointer to buffer for storing random data -- buffer must already |
|
* exist |
|
* @len [in] size of the buffer, specifying also the requested number of random |
|
* in bytes |
|
* |
|
* @return 0 when request is fulfilled or an error |
|
* |
|
* The following error codes can occur: |
|
* -1 entropy_collector is NULL |
|
* -2 RCT failed |
|
* -3 APT test failed |
|
*/ |
|
int jent_read_entropy(struct rand_data *ec, unsigned char *data, |
|
unsigned int len) |
|
{ |
|
unsigned char *p = data; |
|
|
|
if (!ec) |
|
return -1; |
|
|
|
while (len > 0) { |
|
unsigned int tocopy; |
|
|
|
jent_gen_entropy(ec); |
|
|
|
if (jent_health_failure(ec)) { |
|
int ret; |
|
|
|
if (jent_rct_failure(ec)) |
|
ret = -2; |
|
else |
|
ret = -3; |
|
|
|
/* |
|
* Re-initialize the noise source |
|
* |
|
* If the health test fails, the Jitter RNG remains |
|
* in failure state and will return a health failure |
|
* during next invocation. |
|
*/ |
|
if (jent_entropy_init()) |
|
return ret; |
|
|
|
/* Set APT to initial state */ |
|
jent_apt_reset(ec, 0); |
|
ec->apt_base_set = 0; |
|
|
|
/* Set RCT to initial state */ |
|
ec->rct_count = 0; |
|
|
|
/* Re-enable Jitter RNG */ |
|
ec->health_failure = 0; |
|
|
|
/* |
|
* Return the health test failure status to the |
|
* caller as the generated value is not appropriate. |
|
*/ |
|
return ret; |
|
} |
|
|
|
if ((DATA_SIZE_BITS / 8) < len) |
|
tocopy = (DATA_SIZE_BITS / 8); |
|
else |
|
tocopy = len; |
|
jent_memcpy(p, &ec->data, tocopy); |
|
|
|
len -= tocopy; |
|
p += tocopy; |
|
} |
|
|
|
return 0; |
|
} |
|
|
|
/*************************************************************************** |
|
* Initialization logic |
|
***************************************************************************/ |
|
|
|
struct rand_data *jent_entropy_collector_alloc(unsigned int osr, |
|
unsigned int flags) |
|
{ |
|
struct rand_data *entropy_collector; |
|
|
|
entropy_collector = jent_zalloc(sizeof(struct rand_data)); |
|
if (!entropy_collector) |
|
return NULL; |
|
|
|
if (!(flags & JENT_DISABLE_MEMORY_ACCESS)) { |
|
/* Allocate memory for adding variations based on memory |
|
* access |
|
*/ |
|
entropy_collector->mem = jent_zalloc(JENT_MEMORY_SIZE); |
|
if (!entropy_collector->mem) { |
|
jent_zfree(entropy_collector); |
|
return NULL; |
|
} |
|
entropy_collector->memblocksize = JENT_MEMORY_BLOCKSIZE; |
|
entropy_collector->memblocks = JENT_MEMORY_BLOCKS; |
|
entropy_collector->memaccessloops = JENT_MEMORY_ACCESSLOOPS; |
|
} |
|
|
|
/* verify and set the oversampling rate */ |
|
if (osr == 0) |
|
osr = 1; /* minimum sampling rate is 1 */ |
|
entropy_collector->osr = osr; |
|
|
|
/* fill the data pad with non-zero values */ |
|
jent_gen_entropy(entropy_collector); |
|
|
|
return entropy_collector; |
|
} |
|
|
|
void jent_entropy_collector_free(struct rand_data *entropy_collector) |
|
{ |
|
jent_zfree(entropy_collector->mem); |
|
entropy_collector->mem = NULL; |
|
jent_zfree(entropy_collector); |
|
} |
|
|
|
int jent_entropy_init(void) |
|
{ |
|
int i; |
|
__u64 delta_sum = 0; |
|
__u64 old_delta = 0; |
|
unsigned int nonstuck = 0; |
|
int time_backwards = 0; |
|
int count_mod = 0; |
|
int count_stuck = 0; |
|
struct rand_data ec = { 0 }; |
|
|
|
/* Required for RCT */ |
|
ec.osr = 1; |
|
|
|
/* We could perform statistical tests here, but the problem is |
|
* that we only have a few loop counts to do testing. These |
|
* loop counts may show some slight skew and we produce |
|
* false positives. |
|
* |
|
* Moreover, only old systems show potentially problematic |
|
* jitter entropy that could potentially be caught here. But |
|
* the RNG is intended for hardware that is available or widely |
|
* used, but not old systems that are long out of favor. Thus, |
|
* no statistical tests. |
|
*/ |
|
|
|
/* |
|
* We could add a check for system capabilities such as clock_getres or |
|
* check for CONFIG_X86_TSC, but it does not make much sense as the |
|
* following sanity checks verify that we have a high-resolution |
|
* timer. |
|
*/ |
|
/* |
|
* TESTLOOPCOUNT needs some loops to identify edge systems. 100 is |
|
* definitely too little. |
|
* |
|
* SP800-90B requires at least 1024 initial test cycles. |
|
*/ |
|
#define TESTLOOPCOUNT 1024 |
|
#define CLEARCACHE 100 |
|
for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) { |
|
__u64 time = 0; |
|
__u64 time2 = 0; |
|
__u64 delta = 0; |
|
unsigned int lowdelta = 0; |
|
int stuck; |
|
|
|
/* Invoke core entropy collection logic */ |
|
jent_get_nstime(&time); |
|
ec.prev_time = time; |
|
jent_lfsr_time(&ec, time, 0, 0); |
|
jent_get_nstime(&time2); |
|
|
|
/* test whether timer works */ |
|
if (!time || !time2) |
|
return JENT_ENOTIME; |
|
delta = jent_delta(time, time2); |
|
/* |
|
* test whether timer is fine grained enough to provide |
|
* delta even when called shortly after each other -- this |
|
* implies that we also have a high resolution timer |
|
*/ |
|
if (!delta) |
|
return JENT_ECOARSETIME; |
|
|
|
stuck = jent_stuck(&ec, delta); |
|
|
|
/* |
|
* up to here we did not modify any variable that will be |
|
* evaluated later, but we already performed some work. Thus we |
|
* already have had an impact on the caches, branch prediction, |
|
* etc. with the goal to clear it to get the worst case |
|
* measurements. |
|
*/ |
|
if (i < CLEARCACHE) |
|
continue; |
|
|
|
if (stuck) |
|
count_stuck++; |
|
else { |
|
nonstuck++; |
|
|
|
/* |
|
* Ensure that the APT succeeded. |
|
* |
|
* With the check below that count_stuck must be less |
|
* than 10% of the overall generated raw entropy values |
|
* it is guaranteed that the APT is invoked at |
|
* floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times. |
|
*/ |
|
if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) { |
|
jent_apt_reset(&ec, |
|
delta & JENT_APT_WORD_MASK); |
|
if (jent_health_failure(&ec)) |
|
return JENT_EHEALTH; |
|
} |
|
} |
|
|
|
/* Validate RCT */ |
|
if (jent_rct_failure(&ec)) |
|
return JENT_ERCT; |
|
|
|
/* test whether we have an increasing timer */ |
|
if (!(time2 > time)) |
|
time_backwards++; |
|
|
|
/* use 32 bit value to ensure compilation on 32 bit arches */ |
|
lowdelta = time2 - time; |
|
if (!(lowdelta % 100)) |
|
count_mod++; |
|
|
|
/* |
|
* ensure that we have a varying delta timer which is necessary |
|
* for the calculation of entropy -- perform this check |
|
* only after the first loop is executed as we need to prime |
|
* the old_data value |
|
*/ |
|
if (delta > old_delta) |
|
delta_sum += (delta - old_delta); |
|
else |
|
delta_sum += (old_delta - delta); |
|
old_delta = delta; |
|
} |
|
|
|
/* |
|
* we allow up to three times the time running backwards. |
|
* CLOCK_REALTIME is affected by adjtime and NTP operations. Thus, |
|
* if such an operation just happens to interfere with our test, it |
|
* should not fail. The value of 3 should cover the NTP case being |
|
* performed during our test run. |
|
*/ |
|
if (time_backwards > 3) |
|
return JENT_ENOMONOTONIC; |
|
|
|
/* |
|
* Variations of deltas of time must on average be larger |
|
* than 1 to ensure the entropy estimation |
|
* implied with 1 is preserved |
|
*/ |
|
if ((delta_sum) <= 1) |
|
return JENT_EVARVAR; |
|
|
|
/* |
|
* Ensure that we have variations in the time stamp below 10 for at |
|
* least 10% of all checks -- on some platforms, the counter increments |
|
* in multiples of 100, but not always |
|
*/ |
|
if ((TESTLOOPCOUNT/10 * 9) < count_mod) |
|
return JENT_ECOARSETIME; |
|
|
|
/* |
|
* If we have more than 90% stuck results, then this Jitter RNG is |
|
* likely to not work well. |
|
*/ |
|
if ((TESTLOOPCOUNT/10 * 9) < count_stuck) |
|
return JENT_ESTUCK; |
|
|
|
return 0; |
|
}
|
|
|