Re: cvs commit: openssl/doc/crypto BN_rand.pod

[Bodo Moeller]

What about a combined version of BN_rand_range (see below)?  Then
dsa_ossl.c needs just this:

        /* Get random k */
        if (!BN_rand_range(&k, BN_value_one(), dsa->q, NULL)) goto err;



/* random number r:  minimum + offset <= r < range + offset
 * If 'minimum' is used, it should be small!
*/
int BN_rand_range(BIGNUM *r, BIGNUM *minimum, BIGNUM *range, BIGNUM *offset)
        {
        int n;

        if (range->neg || BN_is_zero(range))
                {
                BNerr(BN_F_BN_RAND_RANGE, BN_R_INVALID_RANGE);
                return 0;
                }
        if (minimum && BN_cmp(minimum, range) >= 0)
                {
                BNerr(BN_F_BN_RAND_RANGE, BN_R_INVALID_MINIMUM);
                return 0;
                }

        n = BN_num_bits(range); /* n > 0 */

        if (n == 1)
                {
                if (!BN_zero(r)) return 0;
                }
        else
                do
                {
                if (BN_is_bit_set(range, n - 2))
                        {
                        do
                                {
                                /* range = 11..._2, so each iteration succeeds with 
probability >= .75 */
                                if (!BN_rand(r, n, 0, 0)) return 0;
                                }
                        while (BN_cmp(r, range) >= 0);
                        }
                else
                        {
                        /* range = 10..._2,
                         * so  3*range (= 11..._2)  is exactly one bit longer than  
range */
                        do
                                {
                                if (!BN_rand(r, n + 1, 0, 0)) return 0;
                                /* If  r < 3*range,  use  r := r MOD range
                                 * (which is either  r, r - range,  or  r - 2*range).
                                 * Otherwise, iterate once more.
                                 * Since  3*range = 11..._2, each iteration succeeds 
with
                                 * probability >= .75. */
                                if (BN_cmp(r ,range) >= 0)
                                        {
                                        if (!BN_sub(r, r, range)) return 0;
                                        if (BN_cmp(r, range) >= 0)
                                                if (!BN_sub(r, r, range)) return 0;
                                        }
                                }
                        while (BN_cmp(r, range) >= 0);
                        }
                }
                while (minimum && BN_cmp(r, minimum) < 0);

        if (offset != NULL)
                {
                if (!BN_add(r, r, offset)) return 0;
                }
        
        return 1;
        }
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