blob: 712db1706b322d1ffe93fa443b935a1354bbd4bb [file] [log] [blame]
 #include "os.h" #include #define iseven(a) (((a)->p[0] & 1) == 0) /* 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->sign < 0 || b->sign < 0){ mpassign(mpzero, v); mpassign(mpzero, y); mpassign(mpzero, x); return; } 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); return; }