random.c

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/*
random.c

Random number generator.

The random number generator collects data from the kernel and compressed
that data into a seed for a psuedo random number generator.
*/

#include "../drivers.h"
#include "../../kernel/const.h"
#include "assert.h"

#include "random.h"
#include "sha2.h"
#include "aes/rijndael.h"

#define N_DERIV 16
#define NR_POOLS 32
#define MIN_SAMPLES     256     /* Number of samples needed in pool 0 for a
                                 * re-seed.
                                 */

PRIVATE unsigned long deriv[RANDOM_SOURCES][N_DERIV];
PRIVATE int pool_ind[RANDOM_SOURCES];
PRIVATE SHA256_CTX pool_ctx[NR_POOLS];
PRIVATE unsigned samples= 0;
PRIVATE int got_seeded= 0;
PRIVATE u8_t random_key[2*AES_BLOCKSIZE];
PRIVATE u32_t count_lo, count_hi;
PRIVATE u32_t reseed_count;

FORWARD _PROTOTYPE( void add_sample, (int source, unsigned long sample) );
FORWARD _PROTOTYPE( void data_block, (rd_keyinstance *keyp,
                                                        void *data)     );
FORWARD _PROTOTYPE( void reseed, (void)                                 );

PUBLIC void random_init()
{
        int i, j;

        assert(&deriv[RANDOM_SOURCES-1][N_DERIV-1] ==
                &deriv[0][0] + RANDOM_SOURCES*N_DERIV -1);

        for (i= 0; i<RANDOM_SOURCES; i++)
        {
                for (j= 0; j<N_DERIV; j++)
                        deriv[i][j]= 0;
                pool_ind[i]= 0;
        }
        for (i= 0; i<NR_POOLS; i++)
                SHA256_Init(&pool_ctx[i]);
        count_lo= 0;
        count_hi= 0;
        reseed_count= 0;
}

PUBLIC int random_isseeded()
{
        if (got_seeded)
                return 1;
        return 0;
}

PUBLIC void random_update(source, buf, count)
int source;
unsigned short *buf;
int count;
{
        int i;

#if 0
        printf("random_update: got %d samples for source %d\n", count, source);
#endif
        if (source < 0 || source >= RANDOM_SOURCES)
                panic("memory", "random_update: bad source", source);
        for (i= 0; i<count; i++)
                add_sample(source, buf[i]);
        reseed();
}

PUBLIC void random_getbytes(buf, size)
void *buf;
size_t size;
{
        int n, r;
        u8_t *cp;
        rd_keyinstance key;
        u8_t output[AES_BLOCKSIZE];

        r= rijndael_makekey(&key, sizeof(random_key), random_key);
        assert(r == 0);

        cp= buf;
        while (size > 0)
        {
                n= AES_BLOCKSIZE;
                if (n > size)
                {
                        n= size;
                        data_block(&key, output);
                        memcpy(cp, output, n);
                }
                else
                        data_block(&key, cp);
                cp += n;
                size -= n;
        }

        /* Generate new key */
        assert(sizeof(random_key) == 2*AES_BLOCKSIZE);
        data_block(&key, random_key);
        data_block(&key, random_key+AES_BLOCKSIZE);
}

PUBLIC void random_putbytes(buf, size)
void *buf;
size_t size;
{
        /* Add bits to pool zero */
        SHA256_Update(&pool_ctx[0], buf, size);

        /* Assume that these bits are truely random. Increment samples
         * with the number of bits.
         */
        samples += size*8;

        reseed();
}

PRIVATE void add_sample(source, sample)
int source;
unsigned long sample;
{
        int i, pool_nr;
        unsigned long d, v, di, min;

        /* Delete bad sample. Compute the Nth derivative. Delete the sample
         * if any derivative is too small.
         */
        min= (unsigned long)-1;
        v= sample;
        for (i= 0; i<N_DERIV; i++)
        {
                di= deriv[source][i];

                /* Compute the difference */
                if (v >= di)
                        d= v-di;
                else
                        d= di-v;
                deriv[source][i]= v;
                v= d;
                if (v <min)
                        min= v;
        }
        if (min < 2)
        {
#if 0
                printf("ignoring sample '%u' from source %d\n",
                        sample, source);
#endif
                return;
        }
#if 0
        printf("accepting sample '%u' from source %d\n", sample, source);
#endif

        pool_nr= pool_ind[source];
        assert(pool_nr >= 0 && pool_nr < NR_POOLS);

        SHA256_Update(&pool_ctx[pool_nr], (unsigned char *)&sample,
                sizeof(sample));
        if (pool_nr == 0)
                samples++;
        pool_nr++;
        if (pool_nr >= NR_POOLS)
                pool_nr= 0;
        pool_ind[source]= pool_nr;
}

PRIVATE void data_block(keyp, data)
rd_keyinstance *keyp;
void *data;
{
        int r;
        u8_t input[AES_BLOCKSIZE];

        memset(input, '\0', sizeof(input));

        /* Do we want the output of the random numbers to be portable 
         * across platforms (for example for RSA signatures)? At the moment
         * we don't do anything special. Encrypt the counter with the AES
         * key.
         */
        assert(sizeof(count_lo)+sizeof(count_hi) <= AES_BLOCKSIZE);
        memcpy(input, &count_lo, sizeof(count_lo));
        memcpy(input+sizeof(count_lo), &count_hi, sizeof(count_hi));
        r= rijndael_ecb_encrypt(keyp, input, data, AES_BLOCKSIZE, NULL);
        assert(r == AES_BLOCKSIZE);

        count_lo++;
        if (count_lo == 0)
                count_hi++;
}

PRIVATE void reseed()
{
        int i;
        SHA256_CTX ctx;
        u8_t digest[SHA256_DIGEST_LENGTH];

        if (samples < MIN_SAMPLES)
                return;

        reseed_count++;
        SHA256_Init(&ctx);
        if (got_seeded)
                SHA256_Update(&ctx, random_key, sizeof(random_key));
        SHA256_Final(digest, &pool_ctx[0]);
        SHA256_Update(&ctx, digest, sizeof(digest));
        SHA256_Init(&pool_ctx[0]);
        for (i= 1; i<NR_POOLS; i++)
        {
                if ((reseed_count & (1UL << (i-1))) != 0)
                        break;
                SHA256_Final(digest, &pool_ctx[i]);
                SHA256_Update(&ctx, digest, sizeof(digest));
                SHA256_Init(&pool_ctx[i]);
        }
        SHA256_Final(digest, &ctx);
        assert(sizeof(random_key) == sizeof(digest));
        memcpy(random_key, &digest, sizeof(random_key));
        samples= 0;

        got_seeded= 1;
}

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