89 lines
1.4 KiB
C
89 lines
1.4 KiB
C
#include "os.h"
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#include <mp.h>
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// extended euclid
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//
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// For a and b it solves, d = gcd(a,b) and finds x and y s.t.
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// ax + by = d
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//
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// Handbook of Applied Cryptography, Menezes et al, 1997, pg 67
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void
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mpeuclid(mpint *a, mpint *b, mpint *d, mpint *x, mpint *y)
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{
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mpint *tmp, *x0, *x1, *x2, *y0, *y1, *y2, *q, *r;
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assert((a->flags&b->flags) & MPnorm);
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assert(((a->flags|b->flags|d->flags|x->flags|y->flags) & MPtimesafe) == 0);
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if(a->sign<0 || b->sign<0)
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jehanne_sysfatal("mpeuclid: negative arg");
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if(mpcmp(a, b) < 0){
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tmp = a;
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a = b;
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b = tmp;
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tmp = x;
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x = y;
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y = tmp;
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}
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if(b->top == 0){
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mpassign(a, d);
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mpassign(mpone, x);
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mpassign(mpzero, y);
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return;
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}
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a = mpcopy(a);
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b = mpcopy(b);
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x0 = mpnew(0);
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x1 = mpcopy(mpzero);
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x2 = mpcopy(mpone);
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y0 = mpnew(0);
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y1 = mpcopy(mpone);
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y2 = mpcopy(mpzero);
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q = mpnew(0);
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r = mpnew(0);
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while(b->top != 0 && b->sign > 0){
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// q = a/b
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// r = a mod b
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mpdiv(a, b, q, r);
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// x0 = x2 - qx1
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mpmul(q, x1, x0);
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mpsub(x2, x0, x0);
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// y0 = y2 - qy1
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mpmul(q, y1, y0);
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mpsub(y2, y0, y0);
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// rotate values
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tmp = a;
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a = b;
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b = r;
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r = tmp;
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tmp = x2;
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x2 = x1;
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x1 = x0;
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x0 = tmp;
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tmp = y2;
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y2 = y1;
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y1 = y0;
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y0 = tmp;
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}
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mpassign(a, d);
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mpassign(x2, x);
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mpassign(y2, y);
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mpfree(x0);
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mpfree(x1);
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mpfree(x2);
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mpfree(y0);
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mpfree(y1);
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mpfree(y2);
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mpfree(q);
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mpfree(r);
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mpfree(a);
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mpfree(b);
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}
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