org.whispersystems.curve25519.java.ge_frombytes Maven / Gradle / Ivy

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Curve25519 library for Java

There is a newer version: 0.5.0

package org.whispersystems.curve25519.java;

public class ge_frombytes {

//CONVERT #include "ge.h"

static int[] d = {
//CONVERT #include "d.h"
-10913610,13857413,-15372611,6949391,114729,-8787816,-6275908,-3247719,-18696448,-12055116
} ;

static int[] sqrtm1 = {
//CONVERT #include "sqrtm1.h"
-32595792,-7943725,9377950,3500415,12389472,-272473,-25146209,-2005654,326686,11406482
} ;

static int ge_frombytes_negate_vartime(ge_p3 h,byte[] s)
{
  int[] u = new int[10];
  int[] v = new int[10];
  int[] v3 = new int[10];
  int[] vxx = new int[10];
  int[] check = new int[10];

  fe_frombytes.fe_frombytes(h.Y,s);
  fe_1.fe_1(h.Z);
  fe_sq.fe_sq(u,h.Y);
  fe_mul.fe_mul(v,u,d);
  fe_sub.fe_sub(u,u,h.Z);       /* u = y^2-1 */
  fe_add.fe_add(v,v,h.Z);       /* v = dy^2+1 */

  fe_sq.fe_sq(v3,v);
  fe_mul.fe_mul(v3,v3,v);        /* v3 = v^3 */
  fe_sq.fe_sq(h.X,v3);
  fe_mul.fe_mul(h.X,h.X,v);
  fe_mul.fe_mul(h.X,h.X,u);    /* x = uv^7 */

  fe_pow22523.fe_pow22523(h.X,h.X); /* x = (uv^7)^((q-5)/8) */
  fe_mul.fe_mul(h.X,h.X,v3);
  fe_mul.fe_mul(h.X,h.X,u);    /* x = uv^3(uv^7)^((q-5)/8) */

  fe_sq.fe_sq(vxx,h.X);
  fe_mul.fe_mul(vxx,vxx,v);
  fe_sub.fe_sub(check,vxx,u);    /* vx^2-u */
  if (fe_isnonzero.fe_isnonzero(check) != 0) {
    fe_add.fe_add(check,vxx,u);  /* vx^2+u */
    if (fe_isnonzero.fe_isnonzero(check) != 0) return -1;
    fe_mul.fe_mul(h.X,h.X,sqrtm1);
  }

  if (fe_isnegative.fe_isnegative(h.X) == ((s[31] >>> 7) & 0x01)) {
    fe_neg.fe_neg(h.X,h.X);
    }

  fe_mul.fe_mul(h.T,h.X,h.Y);
  return 0;
}


}