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
|
#include "sc25519.h"
/*Arithmetic modulo the group order n = 2^252 + 27742317777372353535851937790883648493
* = 7237005577332262213973186563042994240857116359379907606001950938285454250989
*/
/* Contains order, 2*order, 4*order, 8*order, each represented in 4 consecutive unsigned long long */
static const unsigned long long order[16] = {0x5812631A5CF5D3EDULL, 0x14DEF9DEA2F79CD6ULL,
0x0000000000000000ULL, 0x1000000000000000ULL,
0xB024C634B9EBA7DAULL, 0x29BDF3BD45EF39ACULL,
0x0000000000000000ULL, 0x2000000000000000ULL,
0x60498C6973D74FB4ULL, 0x537BE77A8BDE7359ULL,
0x0000000000000000ULL, 0x4000000000000000ULL,
0xC09318D2E7AE9F68ULL, 0xA6F7CEF517BCE6B2ULL,
0x0000000000000000ULL, 0x8000000000000000ULL};
static unsigned long long smaller(unsigned long long a,unsigned long long b)
{
unsigned long long atop = a >> 32;
unsigned long long abot = a & 4294967295;
unsigned long long btop = b >> 32;
unsigned long long bbot = b & 4294967295;
unsigned long long atopbelowbtop = (atop - btop) >> 63;
unsigned long long atopeqbtop = ((atop ^ btop) - 1) >> 63;
unsigned long long abotbelowbbot = (abot - bbot) >> 63;
return atopbelowbtop | (atopeqbtop & abotbelowbbot);
}
void sc25519_from32bytes(sc25519 *r, const unsigned char x[32])
{
unsigned long long t[4];
unsigned long long b;
unsigned long long mask;
int i, j;
/* assuming little-endian */
r->v[0] = *(unsigned long long *)x;
r->v[1] = *(((unsigned long long *)x)+1);
r->v[2] = *(((unsigned long long *)x)+2);
r->v[3] = *(((unsigned long long *)x)+3);
for(j=3;j>=0;j--)
{
b=0;
for(i=0;i<4;i++)
{
b += order[4*j+i]; /* no overflow for this particular order */
t[i] = r->v[i] - b;
b = smaller(r->v[i],b);
}
mask = b - 1;
for(i=0;i<4;i++)
r->v[i] ^= mask & (r->v[i] ^ t[i]);
}
}
|
