123 lines
2.0 KiB
C
123 lines
2.0 KiB
C
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#include "os.h"
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#include <mp.h>
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#include <libsec.h>
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// chinese remainder theorem
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//
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// handbook of applied cryptography, menezes et al, 1997, pp 610 - 613
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struct CRTpre
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{
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int n; // number of moduli
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mpint **m; // pointer to moduli
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mpint **c; // precomputed coefficients
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mpint **p; // precomputed products
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mpint *a[1]; // local storage
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};
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// setup crt info, returns a newly created structure
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CRTpre*
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crtpre(int n, mpint **m)
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{
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CRTpre *crt;
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int i, j;
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mpint *u;
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crt = malloc(sizeof(CRTpre)+sizeof(mpint)*3*n);
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if(crt == nil)
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sysfatal("crtpre: %r");
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crt->m = crt->a;
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crt->c = crt->a+n;
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crt->p = crt->c+n;
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crt->n = n;
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// make a copy of the moduli
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for(i = 0; i < n; i++)
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crt->m[i] = mpcopy(m[i]);
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// precompute the products
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u = mpcopy(mpone);
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for(i = 0; i < n; i++){
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mpmul(u, m[i], u);
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crt->p[i] = mpcopy(u);
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}
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// precompute the coefficients
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for(i = 1; i < n; i++){
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crt->c[i] = mpcopy(mpone);
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for(j = 0; j < i; j++){
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mpinvert(m[j], m[i], u);
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mpmul(u, crt->c[i], u);
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mpmod(u, m[i], crt->c[i]);
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}
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}
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mpfree(u);
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return crt;
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}
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void
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crtprefree(CRTpre *crt)
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{
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int i;
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for(i = 0; i < crt->n; i++){
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if(i != 0)
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mpfree(crt->c[i]);
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mpfree(crt->p[i]);
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mpfree(crt->m[i]);
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}
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free(crt);
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}
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// convert to residues, returns a newly created structure
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CRTres*
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crtin(CRTpre *crt, mpint *x)
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{
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int i;
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CRTres *res;
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res = malloc(sizeof(CRTres)+sizeof(mpint)*crt->n);
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if(res == nil)
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sysfatal("crtin: %r");
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res->n = crt->n;
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for(i = 0; i < res->n; i++){
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res->r[i] = mpnew(0);
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mpmod(x, crt->m[i], res->r[i]);
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}
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return res;
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}
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// garners algorithm for converting residue form to linear
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void
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crtout(CRTpre *crt, CRTres *res, mpint *x)
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{
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mpint *u;
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int i;
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u = mpnew(0);
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mpassign(res->r[0], x);
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for(i = 1; i < crt->n; i++){
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mpsub(res->r[i], x, u);
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mpmul(u, crt->c[i], u);
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mpmod(u, crt->m[i], u);
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mpmul(u, crt->p[i-1], u);
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mpadd(x, u, x);
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}
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mpfree(u);
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}
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// free the residue
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void
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crtresfree(CRTres *res)
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{
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int i;
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for(i = 0; i < res->n; i++)
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mpfree(res->r[i]);
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free(res);
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}
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