randLIB.c

00001 /*
00002  * Copyright (c) 2014-2015 ARM Limited. All rights reserved.
00003  * SPDX-License-Identifier: Apache-2.0
00004  * Licensed under the Apache License, Version 2.0 (the License); you may
00005  * not use this file except in compliance with the License.
00006  * You may obtain a copy of the License at
00007  *
00008  * http://www.apache.org/licenses/LICENSE-2.0
00009  *
00010  * Unless required by applicable law or agreed to in writing, software
00011  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
00012  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00013  * See the License for the specific language governing permissions and
00014  * limitations under the License.
00015  */
00016 #include <stdint.h>
00017 #include <stdlib.h>
00018 #include <stdbool.h>
00019 #include <limits.h>
00020 #include "randLIB.h"
00021 #include "platform/arm_hal_random.h"
00022 
00023 #if ((RAND_MAX+1) & RAND_MAX) != 0
00024 #error "RAND_MAX isn't 2^n-1 :("
00025 #endif
00026 
00027 /**
00028  * This library is made for getting random numbers for Timing needs in protocols.
00029  *
00030  * **not safe to use for security or cryptographic operations.**
00031  *
00032  */
00033 
00034 
00035 /**
00036   * \brief Init seed for Pseudo Random.
00037   *
00038   * \return None
00039   *
00040   */
00041 void randLIB_seed_random(void)
00042 {
00043     uint32_t rand_seed;
00044     arm_random_module_init();
00045     rand_seed = arm_random_seed_get();
00046     srand(rand_seed);
00047 }
00048 
00049 /**
00050   * \brief Generate 8-bit random number.
00051   *
00052   * \param None
00053   * \return 8-bit random number
00054   *
00055   */
00056 uint8_t randLIB_get_8bit(void)
00057 {
00058     return rand();
00059 }
00060 
00061 /**
00062   * \brief Generate 16-bit random number.
00063   *
00064   * \param None
00065   * \return 16-bit random number
00066   *
00067   */
00068 uint16_t randLIB_get_16bit(void)
00069 {
00070     uint16_t ret_val;
00071 
00072     ret_val = rand();
00073 #if RAND_MAX == 0x7FFF
00074     ret_val |= (uint16_t) rand() << 15;
00075 #endif
00076 
00077     return ret_val;
00078 }
00079 /**
00080   * \brief Generate 32-bit random number.
00081   *
00082   * \param None
00083   * \return 32-bit random number
00084   *
00085   */
00086 uint32_t randLIB_get_32bit(void)
00087 {
00088     uint32_t ret_val;
00089 
00090     ret_val = rand();
00091 #if RAND_MAX == 0x7FFF
00092     ret_val |= (uint32_t) rand() << 15;
00093     ret_val |= (uint32_t) rand() << 30;
00094 #elif RAND_MAX == 0x3FFFFFFF /* IAR */
00095     ret_val |= (uint32_t) rand() << 30;
00096 #elif RAND_MAX == 0x7FFFFFFF
00097     ret_val |= (uint32_t) rand() << 31;
00098 #else
00099 #error "randLIB_get_32bit - odd RAND_MAX"
00100 #endif
00101 
00102     return ret_val;
00103 }
00104 
00105 
00106 /**
00107   * \brief Generate n-bytes random numbers.
00108   *
00109   * \param data_ptr pointer where random will be stored
00110   * \param eight_bit_boundary how many bytes need random
00111   * \return 0 process valid
00112   * \return -1 Unsupported Parameters
00113   *
00114   */
00115 int8_t randLIB_get_n_bytes_random(uint8_t *data_ptr, uint8_t eight_bit_boundary)
00116 {
00117     if ((data_ptr == 0) || (eight_bit_boundary == 0)) {
00118         return -1;
00119     }
00120 
00121     while (eight_bit_boundary) {
00122         *data_ptr++ = randLIB_get_8bit();
00123         eight_bit_boundary--;
00124     }
00125     return 0;
00126 }
00127 
00128 /**
00129   * \brief Generate a random number within a range.
00130   *
00131   * The result is linearly distributed in the range [min..max], inclusive.
00132   *
00133   * \param min minimum value that can be generated
00134   * \param max maximum value that can be generated
00135   */
00136 uint16_t randLIB_get_random_in_range(uint16_t min, uint16_t max)
00137 {
00138     /* This special case is potentially common, particularly in this routine's
00139      * first user (Trickle), so worth catching immediately */
00140     if (min == max) {
00141         return min;
00142     }
00143 
00144     /* 16-bit arithmetic below fails in this extreme case; we can optimise it */
00145     if (max - min == 0xFFFF) {
00146         return randLIB_get_16bit();
00147     }
00148 
00149     /* We get RAND_MAX+1 values from rand() in the range [0..RAND_MAX], and
00150      * need to divvy them up into the number of values we need. And reroll any
00151      * odd values off the end as we insist every value having equal chance.
00152      *
00153      * Special handling for systems where RAND_MAX is 0x7FFF; we use our
00154      * randLIB_get_16bit() and have to be a bit more careful about
00155      * unsigned integer overflow. (On other systems rand() returns int,
00156      * so we can't overflow if we use unsigned int).
00157      *
00158      * Eg, range(1,3), RAND_MAX = 0x7FFFFFFF:
00159      * We have 3 bands of size 0x2AAAAAAA (0x80000000/3).
00160      *
00161      * We roll: 0x00000000..0x2AAAAAAA9 -> 1
00162      *          0x2AAAAAAA..0x555555553 -> 2
00163      *          0x55555554..0x7FFFFFFFD -> 3
00164      *          0x7FFFFFFE..0x7FFFFFFFF -> reroll
00165      *
00166      * (Bias problem clearly pretty insignificant there, but gets worse as
00167      * range increases).
00168      */
00169     unsigned int values_needed = max + 1 - min;
00170 #if RAND_MAX > 0xFFFF
00171     unsigned int band_size = (RAND_MAX + 1u) / values_needed;
00172 #elif UINT_MAX > 0xFFFF
00173     unsigned int band_size = 0x10000u / values_needed;
00174 #else
00175     /* Avoid the need for long division, at the expense of fractionally
00176      * increasing reroll chance. */
00177     unsigned int band_size = 0xFFFFu / values_needed;
00178 #endif
00179     unsigned int top_of_bands = band_size * values_needed;
00180     unsigned int result;
00181     do {
00182 #if RAND_MAX > 0xFFFF
00183         result = rand();
00184 #else
00185         result = randLIB_get_16bit();
00186 #endif
00187     } while (result >= top_of_bands);
00188 
00189     return min + (uint16_t)(result / band_size);
00190 }
00191 
00192 /**
00193   * \brief Randomise a base 32-bit number by a jitter factor
00194   *
00195   * The result is linearly distributed in the jitter range, which is expressed
00196   * as fixed-point unsigned 1.15 values. For example, to produce a number in the
00197   * range [0.75 * base, 1.25 * base], set min_factor to 0x6000 and max_factor to
00198   * 0xA000.
00199   *
00200   * Result is clamped to 0xFFFFFFFF if it overflows.
00201   *
00202   * \param base The base 32-bit value
00203   * \param min_factor The minimum value for the random factor
00204   * \param max_factor The maximum value for the random factor
00205   */
00206 uint32_t randLIB_randomise_base(uint32_t base, uint16_t min_factor, uint16_t max_factor)
00207 {
00208     uint16_t random_factor = randLIB_get_random_in_range(min_factor, max_factor);
00209 
00210     /* 32x16-bit long multiplication, to get 48-bit result */
00211     uint32_t hi = (base >> 16) * random_factor;
00212     uint32_t lo = (base & 0xFFFF) * random_factor;
00213     /* Add halves, and take top 32 bits of 48-bit result */
00214     uint32_t res = hi + (lo >> 16);
00215 
00216     /* Randomisation factor is *2^15, so need to shift up 1 more bit, avoiding overflow */
00217     if (res & 0x80000000) {
00218         res = 0xFFFFFFFF;
00219     } else {
00220         res = (res << 1) | ((lo >> 15) & 1);
00221     }
00222 
00223     return res;
00224 }