// find a prime p of length n and a generator alpha of Z^*_p
// Alg 4.86 Menezes et al () Handbook, p.164
void
gensafeprime(mpint *p, mpint *alpha, int n, int accuracy)
{
mpint *q, *b;
q = mpnew(n-1);
while(1){
genprime(q, n-1, accuracy);
mpleft(q, 1, p);
mpadd(p, mpone, p); // p = 2*q+1
if(probably_prime(p, accuracy))
break;
}
// now find a generator alpha of the multiplicative
// group Z*_p of order p-1=2q
b = mpnew(0);
while(1){
mprand(n, genrandom, alpha);
mpmod(alpha, p, alpha);
mpmul(alpha, alpha, b);
mpmod(b, p, b);
if(mpcmp(b, mpone) == 0)
continue;
mpexp(alpha, q, p, b);
if(mpcmp(b, mpone) != 0)
break;
}
mpfree(b);
mpfree(q);
}
void
testshift(char *str)
{
mpint *b1, *b2;
int i;
b1 = strtomp(str, nil, 16, nil);
malloccheck();
fprint(2, "A");
b2 = mpnew(0);
fprint(2, "B");
malloccheck();
mpleft(b1, 20, b2);
fprint(2, "C");
malloccheck();
mpfree(b1);
fprint(2, "D");
malloccheck();
mpfree(b2);
}
void
ecadd(ECdomain *dom, ECpoint *a, ECpoint *b, ECpoint *s)
{
mpint *l, *k, *sx, *sy;
if(a->inf && b->inf){
s->inf = 1;
return;
}
if(a->inf){
ecassign(dom, b, s);
return;
}
if(b->inf){
ecassign(dom, a, s);
return;
}
if(mpcmp(a->x, b->x) == 0 && (mpcmp(a->y, mpzero) == 0 || mpcmp(a->y, b->y) != 0)){
s->inf = 1;
return;
}
l = mpnew(0);
k = mpnew(0);
sx = mpnew(0);
sy = mpnew(0);
if(mpcmp(a->x, b->x) == 0 && mpcmp(a->y, b->y) == 0){
mpadd(mpone, mptwo, k);
mpmul(a->x, a->x, l);
mpmul(l, k, l);
mpadd(l, dom->a, l);
mpleft(a->y, 1, k);
mpmod(k, dom->p, k);
mpinvert(k, dom->p, k);
mpmul(k, l, l);
mpmod(l, dom->p, l);
mpleft(a->x, 1, k);
mpmul(l, l, sx);
mpsub(sx, k, sx);
mpmod(sx, dom->p, sx);
mpsub(a->x, sx, sy);
mpmul(l, sy, sy);
mpsub(sy, a->y, sy);
mpmod(sy, dom->p, sy);
mpassign(sx, s->x);
mpassign(sy, s->y);
mpfree(sx);
mpfree(sy);
mpfree(l);
mpfree(k);
return;
}
mpsub(b->y, a->y, l);
mpmod(l, dom->p, l);
mpsub(b->x, a->x, k);
mpmod(k, dom->p, k);
mpinvert(k, dom->p, k);
mpmul(k, l, l);
mpmod(l, dom->p, l);
mpmul(l, l, sx);
mpsub(sx, a->x, sx);
mpsub(sx, b->x, sx);
mpmod(sx, dom->p, sx);
mpsub(a->x, sx, sy);
mpmul(sy, l, sy);
mpsub(sy, a->y, sy);
mpmod(sy, dom->p, sy);
mpassign(sx, s->x);
mpassign(sy, s->y);
mpfree(sx);
mpfree(sy);
mpfree(l);
mpfree(k);
}
// extended binary gcd
//
// For a anv b it solves, v = gcd(a,b) and finds x and y s.t.
// ax + by = v
//
// Handbook of Applied Cryptography, Menezes et al, 1997, pg 608.
void
mpextendedgcd(mpint *a, mpint *b, mpint *v, mpint *x, mpint *y)
{
mpint *u, *A, *B, *C, *D;
int g;
if(a->top == 0){
mpassign(b, v);
mpassign(mpone, y);
mpassign(mpzero, x);
return;
}
if(b->top == 0){
mpassign(a, v);
mpassign(mpone, x);
mpassign(mpzero, y);
return;
}
g = 0;
a = mpcopy(a);
b = mpcopy(b);
while(iseven(a) && iseven(b)){
mpright(a, 1, a);
mpright(b, 1, b);
g++;
}
u = mpcopy(a);
mpassign(b, v);
A = mpcopy(mpone);
B = mpcopy(mpzero);
C = mpcopy(mpzero);
D = mpcopy(mpone);
for(;;) {
// print("%B %B %B %B %B %B\n", u, v, A, B, C, D);
while(iseven(u)){
mpright(u, 1, u);
if(!iseven(A) || !iseven(B)) {
mpadd(A, b, A);
mpsub(B, a, B);
}
mpright(A, 1, A);
mpright(B, 1, B);
}
// print("%B %B %B %B %B %B\n", u, v, A, B, C, D);
while(iseven(v)){
mpright(v, 1, v);
if(!iseven(C) || !iseven(D)) {
mpadd(C, b, C);
mpsub(D, a, D);
}
mpright(C, 1, C);
mpright(D, 1, D);
}
// print("%B %B %B %B %B %B\n", u, v, A, B, C, D);
if(mpcmp(u, v) >= 0){
mpsub(u, v, u);
mpsub(A, C, A);
mpsub(B, D, B);
} else {
mpsub(v, u, v);
mpsub(C, A, C);
mpsub(D, B, D);
}
if(u->top == 0)
break;
}
mpassign(C, x);
mpassign(D, y);
mpleft(v, g, v);
mpfree(A);
mpfree(B);
mpfree(C);
mpfree(D);
mpfree(u);
mpfree(a);
mpfree(b);
}
void
mpdiv(mpint *dividend, mpint *divisor, mpint *quotient, mpint *remainder)
{
int j, s, vn, sign;
mpdigit qd, *up, *vp, *qp;
mpint *u, *v, *t;
// divide bv zero
if(divisor->top == 0)
sysfatal("mpdiv: divide by zero");
// quick check
if(mpmagcmp(dividend, divisor) < 0){
if(remainder != nil)
mpassign(dividend, remainder);
if(quotient != nil)
mpassign(mpzero, quotient);
return;
}
// D1: shift until divisor, v, has hi bit set (needed to make trial
// divisor accurate)
qd = divisor->p[divisor->top-1];
for(s = 0; (qd & mpdighi) == 0; s++)
qd <<= 1;
u = mpnew((dividend->top+2)*Dbits + s);
if(s == 0 && divisor != quotient && divisor != remainder) {
mpassign(dividend, u);
v = divisor;
} else {
mpleft(dividend, s, u);
v = mpnew(divisor->top*Dbits);
mpleft(divisor, s, v);
}
up = u->p+u->top-1;
vp = v->p+v->top-1;
vn = v->top;
// D1a: make sure high digit of dividend is less than high digit of divisor
if(*up >= *vp){
*++up = 0;
u->top++;
}
// storage for multiplies
t = mpnew(4*Dbits);
qp = nil;
if(quotient != nil){
mpbits(quotient, (u->top - v->top)*Dbits);
quotient->top = u->top - v->top;
qp = quotient->p+quotient->top-1;
}
// D2, D7: loop on length of dividend
for(j = u->top; j > vn; j--){
// D3: calculate trial divisor
mpdigdiv(up-1, *vp, &qd);
// D3a: rule out trial divisors 2 greater than real divisor
if(vn > 1) for(;;){
memset(t->p, 0, 3*Dbytes); // mpvecdigmuladd adds to what's there
mpvecdigmuladd(vp-1, 2, qd, t->p);
if(mpveccmp(t->p, 3, up-2, 3) > 0)
qd--;
else
break;
}
// D4: u -= v*qd << j*Dbits
sign = mpvecdigmulsub(v->p, vn, qd, up-vn);
if(sign < 0){
// D6: trial divisor was too high, add back borrowed
// value and decrease divisor
mpvecadd(up-vn, vn+1, v->p, vn, up-vn);
qd--;
}
// D5: save quotient digit
if(qp != nil)
*qp-- = qd;
// push top of u down one
u->top--;
*up-- = 0;
}
if(qp != nil){
mpnorm(quotient);
if(dividend->sign != divisor->sign)
quotient->sign = -1;
}
if(remainder != nil){
mpright(u, s, remainder); // u is the remainder shifted
remainder->sign = dividend->sign;
}
mpfree(t);
mpfree(u);
if(v != divisor)
mpfree(v);
}
