# shithub: drawterm

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```#include "os.h"
#include <mp.h>
#include <libsec.h>

RSApriv*
rsafill(mpint *n, mpint *e, mpint *d, mpint *p, mpint *q)
{
mpint *c2, *kq, *kp, *x;
RSApriv *rsa;

// make sure we're not being hoodwinked
if(!probably_prime(p, 10) || !probably_prime(q, 10)){
werrstr("rsafill: p or q not prime");
return nil;
}
x = mpnew(0);
mpmul(p, q, x);
if(mpcmp(n, x) != 0){
werrstr("rsafill: n != p*q");
mpfree(x);
return nil;
}
c2 = mpnew(0);
mpsub(p, mpone, c2);
mpsub(q, mpone, x);
mpmul(c2, x, x);
mpmul(e, d, c2);
mpmod(c2, x, x);
if(mpcmp(x, mpone) != 0){
werrstr("rsafill: e*d != 1 mod (p-1)*(q-1)");
mpfree(x);
mpfree(c2);
return nil;
}

// compute chinese remainder coefficient
mpinvert(p, q, c2);

// for crt a**k mod p == (a**(k mod p-1)) mod p
kq = mpnew(0);
kp = mpnew(0);
mpsub(p, mpone, x);
mpmod(d, x, kp);
mpsub(q, mpone, x);
mpmod(d, x, kq);

rsa = rsaprivalloc();
rsa->pub.ek = mpcopy(e);
rsa->pub.n = mpcopy(n);
rsa->dk = mpcopy(d);
rsa->kp = kp;
rsa->kq = kq;
rsa->p = mpcopy(p);
rsa->q = mpcopy(q);
rsa->c2 = c2;

mpfree(x);

return rsa;
}

```