cx_rng.c

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/*******************************************************************************
 *   Ledger Nano S - Secure firmware
 *   (c) 2022 Ledger
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 ********************************************************************************/
 
#include "app_config.h"
 
#ifdef HAVE_RNG
 
#include "cx_ram.h"
#include "cx_utils.h"
#include "cx_crc.h"
#include "lcx_rng.h"
#include "errors.h"
#include "exceptions.h"
 
#include "os_halt.h"
#include "os_math.h"
#include "os_random.h"
#include <string.h>
 
void cx_rng_no_throw(uint8_t *buffer, size_t len)
{
    cx_err_t error;
 
    error = cx_get_random_bytes(buffer, len);
    if (error) {
        /* XXX: calling halt() add a dependency to THROW (os_longjmp). */
        while (1)
            ;
    }
}
 
uint32_t cx_rng_u32_range_func(uint32_t a, uint32_t b, cx_rng_u32_range_randfunc_t randfunc)
{
    uint32_t range = b - a;
    uint32_t r;
 
    if ((range & (range - 1)) == 0) {  // special case: range is a power of 2
        r = randfunc();
        return a + r % range;
    }
 
    uint32_t chunk_size       = UINT32_MAX / range;
    uint32_t last_chunk_value = chunk_size * range;
    r                         = randfunc();
    while (r >= last_chunk_value) {
        r = randfunc();
    }
    return a + r / chunk_size;
}
 
#endif  // HAVE_RNG