mirror of https://github.com/cheat/cheat.git
86 lines
1.8 KiB
Go
86 lines
1.8 KiB
Go
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package x25519
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import (
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"encoding/binary"
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"math/bits"
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fp "github.com/cloudflare/circl/math/fp25519"
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)
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func doubleGeneric(x, z *fp.Elt) {
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t0, t1 := &fp.Elt{}, &fp.Elt{}
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fp.AddSub(x, z)
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fp.Sqr(x, x)
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fp.Sqr(z, z)
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fp.Sub(t0, x, z)
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mulA24Generic(t1, t0)
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fp.Add(t1, t1, z)
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fp.Mul(x, x, z)
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fp.Mul(z, t0, t1)
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}
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func diffAddGeneric(w *[5]fp.Elt, b uint) {
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mu, x1, z1, x2, z2 := &w[0], &w[1], &w[2], &w[3], &w[4]
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fp.Cswap(x1, x2, b)
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fp.Cswap(z1, z2, b)
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fp.AddSub(x1, z1)
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fp.Mul(z1, z1, mu)
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fp.AddSub(x1, z1)
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fp.Sqr(x1, x1)
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fp.Sqr(z1, z1)
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fp.Mul(x1, x1, z2)
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fp.Mul(z1, z1, x2)
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}
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func ladderStepGeneric(w *[5]fp.Elt, b uint) {
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x1, x2, z2, x3, z3 := &w[0], &w[1], &w[2], &w[3], &w[4]
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t0 := &fp.Elt{}
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t1 := &fp.Elt{}
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fp.AddSub(x2, z2)
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fp.AddSub(x3, z3)
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fp.Mul(t0, x2, z3)
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fp.Mul(t1, x3, z2)
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fp.AddSub(t0, t1)
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fp.Cmov(x2, x3, b)
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fp.Cmov(z2, z3, b)
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fp.Sqr(x3, t0)
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fp.Sqr(z3, t1)
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fp.Mul(z3, x1, z3)
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fp.Sqr(x2, x2)
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fp.Sqr(z2, z2)
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fp.Sub(t0, x2, z2)
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mulA24Generic(t1, t0)
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fp.Add(t1, t1, z2)
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fp.Mul(x2, x2, z2)
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fp.Mul(z2, t0, t1)
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}
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func mulA24Generic(z, x *fp.Elt) {
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const A24 = 121666
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const n = 8
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var xx [4]uint64
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for i := range xx {
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xx[i] = binary.LittleEndian.Uint64(x[i*n : (i+1)*n])
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}
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h0, l0 := bits.Mul64(xx[0], A24)
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h1, l1 := bits.Mul64(xx[1], A24)
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h2, l2 := bits.Mul64(xx[2], A24)
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h3, l3 := bits.Mul64(xx[3], A24)
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var c3 uint64
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l1, c0 := bits.Add64(h0, l1, 0)
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l2, c1 := bits.Add64(h1, l2, c0)
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l3, c2 := bits.Add64(h2, l3, c1)
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l4, _ := bits.Add64(h3, 0, c2)
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_, l4 = bits.Mul64(l4, 38)
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l0, c0 = bits.Add64(l0, l4, 0)
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xx[1], c1 = bits.Add64(l1, 0, c0)
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xx[2], c2 = bits.Add64(l2, 0, c1)
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xx[3], c3 = bits.Add64(l3, 0, c2)
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xx[0], _ = bits.Add64(l0, (-c3)&38, 0)
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for i := range xx {
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binary.LittleEndian.PutUint64(z[i*n:(i+1)*n], xx[i])
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}
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}
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