curve_generic.go raw

   1  package x25519
   2  
   3  import (
   4  	"encoding/binary"
   5  	"math/bits"
   6  
   7  	fp "github.com/cloudflare/circl/math/fp25519"
   8  )
   9  
  10  func doubleGeneric(x, z *fp.Elt) {
  11  	t0, t1 := &fp.Elt{}, &fp.Elt{}
  12  	fp.AddSub(x, z)
  13  	fp.Sqr(x, x)
  14  	fp.Sqr(z, z)
  15  	fp.Sub(t0, x, z)
  16  	mulA24Generic(t1, t0)
  17  	fp.Add(t1, t1, z)
  18  	fp.Mul(x, x, z)
  19  	fp.Mul(z, t0, t1)
  20  }
  21  
  22  func diffAddGeneric(w *[5]fp.Elt, b uint) {
  23  	mu, x1, z1, x2, z2 := &w[0], &w[1], &w[2], &w[3], &w[4]
  24  	fp.Cswap(x1, x2, b)
  25  	fp.Cswap(z1, z2, b)
  26  	fp.AddSub(x1, z1)
  27  	fp.Mul(z1, z1, mu)
  28  	fp.AddSub(x1, z1)
  29  	fp.Sqr(x1, x1)
  30  	fp.Sqr(z1, z1)
  31  	fp.Mul(x1, x1, z2)
  32  	fp.Mul(z1, z1, x2)
  33  }
  34  
  35  func ladderStepGeneric(w *[5]fp.Elt, b uint) {
  36  	x1, x2, z2, x3, z3 := &w[0], &w[1], &w[2], &w[3], &w[4]
  37  	t0 := &fp.Elt{}
  38  	t1 := &fp.Elt{}
  39  	fp.AddSub(x2, z2)
  40  	fp.AddSub(x3, z3)
  41  	fp.Mul(t0, x2, z3)
  42  	fp.Mul(t1, x3, z2)
  43  	fp.AddSub(t0, t1)
  44  	fp.Cmov(x2, x3, b)
  45  	fp.Cmov(z2, z3, b)
  46  	fp.Sqr(x3, t0)
  47  	fp.Sqr(z3, t1)
  48  	fp.Mul(z3, x1, z3)
  49  	fp.Sqr(x2, x2)
  50  	fp.Sqr(z2, z2)
  51  	fp.Sub(t0, x2, z2)
  52  	mulA24Generic(t1, t0)
  53  	fp.Add(t1, t1, z2)
  54  	fp.Mul(x2, x2, z2)
  55  	fp.Mul(z2, t0, t1)
  56  }
  57  
  58  func mulA24Generic(z, x *fp.Elt) {
  59  	const A24 = 121666
  60  	const n = 8
  61  	var xx [4]uint64
  62  	for i := range xx {
  63  		xx[i] = binary.LittleEndian.Uint64(x[i*n : (i+1)*n])
  64  	}
  65  
  66  	h0, l0 := bits.Mul64(xx[0], A24)
  67  	h1, l1 := bits.Mul64(xx[1], A24)
  68  	h2, l2 := bits.Mul64(xx[2], A24)
  69  	h3, l3 := bits.Mul64(xx[3], A24)
  70  
  71  	var c3 uint64
  72  	l1, c0 := bits.Add64(h0, l1, 0)
  73  	l2, c1 := bits.Add64(h1, l2, c0)
  74  	l3, c2 := bits.Add64(h2, l3, c1)
  75  	l4, _ := bits.Add64(h3, 0, c2)
  76  	_, l4 = bits.Mul64(l4, 38)
  77  	l0, c0 = bits.Add64(l0, l4, 0)
  78  	xx[1], c1 = bits.Add64(l1, 0, c0)
  79  	xx[2], c2 = bits.Add64(l2, 0, c1)
  80  	xx[3], c3 = bits.Add64(l3, 0, c2)
  81  	xx[0], _ = bits.Add64(l0, (-c3)&38, 0)
  82  	for i := range xx {
  83  		binary.LittleEndian.PutUint64(z[i*n:(i+1)*n], xx[i])
  84  	}
  85  }
  86