blob: cfc1faceee716ee501699cde112dd50add5b88ad (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
|
/*
* BigInt Random Generation
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/bigint.h>
#include <botan/parsing.h>
#include <botan/internal/rounding.h>
namespace Botan {
/*
* Randomize this number
*/
void BigInt::randomize(RandomNumberGenerator& rng,
size_t bitsize, bool set_high_bit)
{
set_sign(Positive);
if(bitsize == 0)
{
clear();
}
else
{
secure_vector<byte> array = rng.random_vec(round_up(bitsize, 8) / 8);
// Always cut unwanted bits
if(bitsize % 8)
array[0] &= 0xFF >> (8 - (bitsize % 8));
// Set the highest bit if wanted
if (set_high_bit)
array[0] |= 0x80 >> ((bitsize % 8) ? (8 - bitsize % 8) : 0);
binary_decode(array);
}
}
/*
* Generate a random integer within given range
*/
BigInt BigInt::random_integer(RandomNumberGenerator& rng,
const BigInt& min, const BigInt& max)
{
BigInt delta_upper_bound = max - min - 1;
if(delta_upper_bound < 0)
throw Invalid_Argument("random_integer: invalid min/max values");
// Choose x in [0, delta_upper_bound]
BigInt x;
do {
auto bitsize = delta_upper_bound.bits();
x.randomize(rng, bitsize, false);
} while(x > delta_upper_bound);
return min + x;
}
}
|
