void ecMultiply (ecPoint *p, const vlPoint k)
/* sets p := k*p */
{
vlPoint h;
int z, hi, ki;
word16 i;
ecPoint r;
gfCopy (r.x, p->x); p->x[0] = 0;
gfCopy (r.y, p->y); p->y[0] = 0;
vlShortMultiply (h, k, 3);
z = vlNumBits (h) - 1; /* so vlTakeBit (h, z) == 1 */
i = 1;
for (;;) {
hi = vlTakeBit (h, i);
ki = vlTakeBit (k, i);
if (hi == 1 && ki == 0) {
ecAdd (p, &r);
}
if (hi == 0 && ki == 1) {
ecSub (p, &r);
}
if (i >= z) {
break;
}
i++;
ecDouble (&r);
}
} /* ecMultiply */
void ecAdd (ecPoint *p, const ecPoint *q)
/* sets p := p + q */
{
gfPoint lambda, t, tx, ty, x3;
/* first check if there is indeed work to do (q != 0): */
if (q->x[0] != 0 || q->y[0] != 0) {
if (p->x[0] != 0 || p->y[0] != 0) {
/* p != 0 and q != 0 */
if (gfEqual (p->x, q->x)) {
/* either p == q or p == -q: */
if (gfEqual (p->y, q->y)) {
/* points are equal; double p: */
ecDouble (p);
} else {
/* must be inverse: result is zero */
/* (should assert that q->y = p->x + p->y) */
p->x[0] = p->y[0] = 0;
}
} else {
/* p != 0, q != 0, p != q, p != -q */
/* evaluate lambda = (y1 + y2)/(x1 + x2): */
gfAdd (ty, p->y, q->y);
gfAdd (tx, p->x, q->x);
gfInvert (t, tx);
gfMultiply (lambda, ty, t);
/* evaluate x3 = lambda^2 + lambda + x1 + x2: */
gfSquare (x3, lambda);
gfAdd (x3, x3, lambda);
gfAdd (x3, x3, tx);
/* evaluate y3 = lambda*(x1 + x3) + x3 + y1: */
gfAdd (tx, p->x, x3);
gfMultiply (t, lambda, tx);
gfAdd (t, t, x3);
gfAdd (p->y, t, p->y);
/* deposit the value of x3: */
gfCopy (p->x, x3);
}
} else {
/* just copy q into p: */
gfCopy (p->x, q->x);
gfCopy (p->y, q->y);
}
}
} /* ecAdd */
void ecSub (ecPoint *p, const ecPoint *r)
/* sets p := p - r */
{
ecPoint t;
gfCopy (t.x, r->x);
gfAdd (t.y, r->x, r->y);
ecAdd (p, &t);
} /* ecSub */
static int gfSlowTrace (const gfPoint p)
/* slowly evaluates to the trace of p (or an error code) */
{
int i;
gfPoint t;
assert (logt != NULL && expt != NULL);
assert (p != NULL);
gfCopy (t, p);
for (i = 1; i < GF_M; i++) {
gfSquare (t, t);
gfAdd (t, t, p);
}
return t[0] != 0;
} /* gfSlowTrace */
void ecDouble (ecPoint *p)
/* sets p := 2*p */
{
gfPoint lambda, t1, t2;
/* evaluate lambda = x + y/x: */
gfInvert (t1, p->x);
gfMultiply (lambda, p->y, t1);
gfAdd (lambda, lambda, p->x);
/* evaluate x3 = lambda^2 + lambda: */
gfSquare (t1, lambda);
gfAdd (t1, t1, lambda); /* now t1 = x3 */
/* evaluate y3 = x^2 + lambda*x3 + x3: */
gfSquare (p->y, p->x);
gfMultiply (t2, lambda, t1);
gfAdd (p->y, p->y, t2);
gfAdd (p->y, p->y, t1);
/* deposit the value of x3: */
gfCopy (p->x, t1);
} /* ecDouble */
void gfSquareRoot (gfPoint p, lunit b)
/* sets p := sqrt(b) = b^(2^(GF_M-1)) */
{
int i;
gfPoint q;
assert (logt != NULL && expt != NULL);
assert (p != NULL);
q[0] = 1; q[1] = b;
if ((GF_M - 1) & 1) {
/* GF_M - 1 is odd */
gfSquare (p, q);
i = GF_M - 2;
} else {
/* GF_M - 1 is even */
gfCopy (p, q);
i = GF_M - 1;
}
while (i) {
gfSquare (p, p);
gfSquare (p, p);
i -= 2;
}
} /* gfSquareRoot */
int gfInvert (gfPoint b, const gfPoint a)
/* sets b := a^(-1) mod (x^GF_K + x^GF_T + 1) */
/* warning: a and b must not overlap! */
{
gfPoint c, f, g;
ltemp x, j, alpha;
assert (logt != NULL && expt != NULL);
assert (b != NULL);
assert (a != NULL);
assert (b != a); /* note that this test is not complete */
if (a[0] == 0) {
/* a is not invertible */
return 1;
}
/* initialize b := 1; c := 0; f := p; g := x^GF_K + x^GF_T + 1: */
b[0] = 1; b[1] = 1;
c[0] = 0;
gfCopy (f, a);
gfClear (g);
g[0] = GF_K + 1; g[1] = 1; g[GF_T + 1] = 1; g[GF_K + 1] = 1;
for (;;) {
if (f[0] == 1) {
assert (f[1] != 0);
gfSmallDiv (b, f[1]);
/* destroy potentially sensitive data: */
gfClear (c); gfClear (f); gfClear (g); x = j = alpha = 0;
return 0;
}
if (f[0] < g[0]) {
goto SWAP_FG;
}
SWAP_GF:
j = f[0] - g[0];
x = logt[f[f[0]]] - logt[g[g[0]]] + TOGGLE;
alpha = expt[x >= TOGGLE ? x - TOGGLE : x];
gfAddMul (f, alpha, j, g);
gfAddMul (b, alpha, j, c);
}
/* basically same code with b,c,f,g swapped */
for (;;) {
if (g[0] == 1) {
assert (g[1] != 0);
gfSmallDiv (c, g[1]);
gfCopy (b, c);
/* destroy potentially sensitive data: */
gfClear (c); gfClear (f); gfClear (g); x = j = alpha = 0;
return 0;
}
if (g[0] < f[0]) {
goto SWAP_GF;
}
SWAP_FG:
j = g[0] - f[0];
x = logt[g[g[0]]] - logt[f[f[0]]] + TOGGLE;
alpha = expt[x >= TOGGLE ? x - TOGGLE : x];
gfAddMul (g, alpha, j, f);
gfAddMul (c, alpha, j, b);
}
} /* gfInvert */
int ecSelfTest (int test_count)
/* perform test_count self tests */
{
int i, yb, nfail = 0, afail = 0, sfail = 0, cfail = 0, qfail = 0, pfail = 0, yfail = 0;
ecPoint f, g, x, y;
vlPoint m, n, p;
clock_t elapsed = 0L;
srand ((unsigned)(time(NULL) % 65521U));
printf ("Executing %d curve self tests...", test_count);
for (i = 0; i < test_count; i++) {
ecRandom (&f);
ecRandom (&g);
vlRandom (m);
vlRandom (n);
/* negation test: -(-f) = f */
ecCopy (&x, &f);
ecNegate (&x);
ecNegate (&x);
if (!ecEqual (&x, &f)) {
nfail++;
/* printf ("Addition test #%d failed!\n", i); */
}
/* addition test: f+g = g+f */
ecCopy (&x, &f); ecAdd (&x, &g);
ecCopy (&y, &g); ecAdd (&y, &f);
if (!ecEqual (&x, &y)) {
afail++;
/* printf ("Addition test #%d failed!\n", i); */
}
/* subtraction test: f-g = f+(-g) */
ecCopy (&x, &f); ecSub (&x, &g);
ecCopy (&y, &g); ecNegate (&y); ecAdd (&y, &f);
if (!ecEqual (&x, &y)) {
sfail++;
/* printf ("Subtraction test #%d failed!\n", i); */
}
/* quadruplication test: 2*(2*f) = f + f + f + f */
ecCopy (&x, &f); ecDouble (&x); ecDouble (&x);
ecClear (&y); ecAdd (&y, &f); ecAdd (&y, &f); ecAdd (&y, &f); ecAdd (&y, &f);
if (!ecEqual (&x, &y)) {
qfail++;
/* printf ("Quadruplication test #%d failed!\n", i); */
}
/* scalar multiplication commutativity test: m*(n*f) = n*(m*f) */
ecCopy (&x, &f);
ecCopy (&y, &f);
elapsed -= clock ();
ecMultiply (&x, n); ecMultiply (&x, m);
ecMultiply (&y, m); ecMultiply (&y, n);
elapsed += clock ();
if (!ecEqual (&x, &y)) {
cfail++;
/* printf ("Commutativity test #%d failed!\n", i); */
}
/* y calculation test: */
yb = ecYbit (&f);
ecClear (&x);
gfCopy (x.x, f.x);
ecCalcY (&x, yb);
if (!ecEqual (&f, &x)) {
yfail++;
/* printf ("Y calculation test #%d failed!\n", i); */
}
/* packing test: unpack (pack (f)) = f */
ecPack (&f, p);
ecUnpack (&x, p);
if (!ecEqual (&f, &x)) {
pfail++;
/* printf ("Packing test #%d failed!\n", i); */
}
}
printf (" done, scalar multiplication time: %.3f s/op.\n",
(float)elapsed/CLOCKS_PER_SEC/(test_count?4*test_count:4));
if (nfail) printf ("---> %d negations failed <---\n", nfail);
if (afail) printf ("---> %d additions failed <---\n", afail);
if (sfail) printf ("---> %d subtractions failed <---\n", sfail);
if (qfail) printf ("---> %d quadruplications failed <---\n", qfail);
if (cfail) printf ("---> %d commutativities failed <---\n", cfail);
if (yfail) printf ("---> %d y calculations failed <---\n", yfail);
if (pfail) printf ("---> %d packings failed <---\n", pfail);
return nfail || afail || sfail || qfail || cfail || yfail || pfail;
} /* ecSelfTest */
void ecCopy (ecPoint *p, const ecPoint *q)
/* sets p := q */
{
gfCopy (p->x, q->x);
gfCopy (p->y, q->y);
} /* ecCopy */
