randpool.c

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#include "randpool.h"
#include "md2.h"

#include <cfg/compiler.h>
#include <cfg/debug.h>       //ASSERT()
#include <cfg/macros.h>      //MIN(), ROUND_UP();

#include <stdio.h>           //sprintf();
#include <string.h>          //memset(), memcpy();

#if CONFIG_RANDPOOL_TIMER
    #include <drv/timer.h>       //timer_clock();
#endif



/*
 * Insert bytes in entropy pool, making a XOR of bytes present
 * in entropy pool.
 */
static void randpool_push(EntropyPool *pool, void *_byte, size_t n_byte)
{
    size_t i = pool->pos_add; // Current number of byte insert in entropy pool.
    uint8_t *byte;

    byte = (uint8_t *)_byte;

    /*
     * Insert a bytes in entropy pool.
     */
    for(size_t j = 0; j < n_byte; j++)
    {
        pool->pool_entropy[i] = pool->pool_entropy[i] ^ byte[j];
        i++;
        i = i % CONFIG_SIZE_ENTROPY_POOL;
    }

    pool->pos_add  =  i; // Update a insert bytes.
}


/*
 * This function stir entropy pool with MD2 function hash.
 *
 */
static void randpool_stir(EntropyPool *pool)
{
    size_t entropy = pool->entropy; //Save current calue of entropy.
    Md2Context context;
    uint8_t tmp_buf[((sizeof(size_t) * 2) + sizeof(int)) * 2 + 1]; //Temporary buffer.

    md2_init(&context); //Init MD2 algorithm.

    randpool_add(pool, NULL, 0);

    for (int i = 0; i < (CONFIG_SIZE_ENTROPY_POOL / MD2_DIGEST_LEN); i++)
    {
        sprintf((char *)tmp_buf, "%0x%0x%0x", pool->counter, i, pool->pos_add);

        /*
         * Hash with MD2 algorithm the entropy pool.
         */
        md2_update(&context, pool->pool_entropy, CONFIG_SIZE_ENTROPY_POOL);

        md2_update(&context, tmp_buf, sizeof(tmp_buf) - 1);

        /*Insert a message digest in entropy pool.*/
        randpool_push(pool, md2_end(&context), MD2_DIGEST_LEN);

        pool->counter = pool->counter + 1;

    }

    /*Insert in pool the difference between a two call of this function (see above).*/
    randpool_add(pool, NULL, 0);

    pool->entropy = entropy; //Restore old value of entropy. We haven't add entropy.
}

void randpool_add(EntropyPool *pool, void *data, size_t entropy)
{
    uint8_t sep[] = "\xaa\xaa\xaa\xaa";  // ??
    size_t data_len = ROUND_UP(entropy, 8) / 8; //Number of entropy byte in input.

    randpool_push(pool, data, data_len); //Insert data to entropy pool.

#if CONFIG_RANDPOOL_TIMER

    ticks_t event = timer_clock();
    ticks_t delta;

    /*Difference of time between a two accese to entropy pool.*/
    delta = event - pool->last_counter;

    randpool_push(pool, &event, sizeof(ticks_t));
    randpool_push(pool, sep, sizeof(sep) - 1); // ??
    randpool_push(pool, &delta, sizeof(delta));

    /*
     * Count of number entropy bit add with delta.
     */
    delta = delta & 0xff;
    while(delta)
    {
        delta >>= 1;
        entropy++;
    }

    pool->last_counter = event;

#endif

    pool->entropy += entropy;      //Update a entropy of the pool.
}

void randpool_init(EntropyPool *pool, void *_data, size_t len)
{
    uint8_t *data;

    data = (uint8_t *)_data;

    memset(pool, 0, sizeof(EntropyPool));
    pool->pos_get = MD2_DIGEST_LEN;

#if CONFIG_RANDPOOL_TIMER
    pool->last_counter = timer_clock();
#endif

    if(data)
    {
        /*
         * Initialize a entropy pool with a
         * previous pool, and assume all pool as
         * entropy.
         */
        len = MIN(len,(size_t)CONFIG_SIZE_ENTROPY_POOL);
        memcpy(pool->pool_entropy, data, len);
        pool->entropy = len;
    }

}

size_t randpool_size(EntropyPool *pool)
{
    return pool->entropy;
}

void randpool_get(EntropyPool *pool, void *_data, size_t n_byte)
{
    Md2Context context;
    size_t i = pool->pos_get;
    size_t n = n_byte;
    size_t pos_write = 0;  //Number of block has been written in data.
    size_t len = MIN((size_t)MD2_DIGEST_LEN, n_byte);
    uint8_t *data;

    data = (uint8_t *)_data;

    /* Test if i + CONFIG_MD2_BLOCK_LEN  is inside of entropy pool.*/
    ASSERT((MD2_DIGEST_LEN + i) <= CONFIG_SIZE_ENTROPY_POOL);

    md2_init(&context);

    while(n > 0)
    {

        /*Hash previous state of pool*/
        md2_update(&context, &pool->pool_entropy[i], MD2_DIGEST_LEN);

        memcpy(&data[pos_write], md2_end(&context), len);

        pos_write += len;   //Update number of block has been written in data.
        n -= len;           //Number of byte copied in data.

        len = MIN(n,(size_t)MD2_DIGEST_LEN);

        i = (i + MD2_DIGEST_LEN) % CONFIG_SIZE_ENTROPY_POOL;

        /* If we haven't more entropy pool to hash, we stir it.*/
        if(i < MD2_DIGEST_LEN)
        {
            randpool_stir(pool);
            i = pool->pos_get;
        }

    }

    pool->pos_get = i; //Current number of byte we get from pool.
    pool->entropy -= n_byte; //Update a entropy.

}

uint8_t *randpool_pool(EntropyPool *pool)
{
    return pool->pool_entropy;
}