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group: adds a function for sampling non-zero scalars. #305

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Dec 2, 2021
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group: adds a function for sampling non-zero scalars. #305

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4 changes: 2 additions & 2 deletions go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,6 @@ go 1.15

require (
github.com/bwesterb/go-ristretto v1.2.1
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519
golang.org/x/sys v0.0.0-20211007075335-d3039528d8ac
golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871
golang.org/x/sys v0.0.0-20211124211545-fe61309f8881
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Is this intentional?

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Yes

)
15 changes: 7 additions & 8 deletions go.sum
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Original file line number Diff line number Diff line change
@@ -1,14 +1,13 @@
github.com/bwesterb/go-ristretto v1.2.0 h1:xxWOVbN5m8NNKiSDZXE1jtZvZnC6JSJ9cYFADiZcWtw=
github.com/bwesterb/go-ristretto v1.2.0/go.mod h1:fUIoIZaG73pV5biE2Blr2xEzDoMj7NFEuV9ekS419A0=
github.com/bwesterb/go-ristretto v1.2.1 h1:Xd9ZXmjKE2aY8Ub7+4bX7tXsIPsV1pIZaUlJUjI1toE=
github.com/bwesterb/go-ristretto v1.2.1/go.mod h1:fUIoIZaG73pV5biE2Blr2xEzDoMj7NFEuV9ekS419A0=
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519 h1:7I4JAnoQBe7ZtJcBaYHi5UtiO8tQHbUSXxL+pnGRANg=
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871 h1:/pEO3GD/ABYAjuakUS6xSEmmlyVS4kxBNkeA9tLJiTI=
golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20211007075335-d3039528d8ac h1:oN6lz7iLW/YC7un8pq+9bOLyXrprv2+DKfkJY+2LJJw=
golang.org/x/sys v0.0.0-20211007075335-d3039528d8ac/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20211124211545-fe61309f8881 h1:TyHqChC80pFkXWraUUf6RuB5IqFdQieMLwwCJokV2pc=
golang.org/x/sys v0.0.0-20211124211545-fe61309f8881/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
1 change: 1 addition & 0 deletions group/group.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ type Group interface {
Order() Scalar
RandomElement(io.Reader) Element
RandomScalar(io.Reader) Scalar
RandomNonZeroScalar(io.Reader) Scalar
HashToElement(data, dst []byte) Element
HashToElementNonUniform(b, dst []byte) Element
HashToScalar(data, dst []byte) Scalar
Expand Down
13 changes: 12 additions & 1 deletion group/ristretto255.go
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Expand Up @@ -3,6 +3,7 @@ package group
import (
"crypto"
_ "crypto/sha512" // to link libraries
"fmt"
"io"

r255 "github.com/bwesterb/go-ristretto"
Expand Down Expand Up @@ -75,13 +76,22 @@ func (g ristrettoGroup) RandomElement(r io.Reader) Element {
}
}

func (g ristrettoGroup) RandomScalar(r io.Reader) Scalar {
func (g ristrettoGroup) RandomScalar(io.Reader) Scalar {
var x r255.Scalar
x.Rand()
return &ristrettoScalar{
s: x,
}
}
func (g ristrettoGroup) RandomNonZeroScalar(io.Reader) Scalar {
var s r255.Scalar
for {
s.Rand()
if s.IsNonZeroI() == 1 {
return &ristrettoScalar{s}
}
}
}
func (g ristrettoGroup) HashToElementNonUniform(b, dst []byte) Element {
return g.HashToElement(b, dst)
}
Expand Down Expand Up @@ -145,6 +155,7 @@ func (e *ristrettoElement) UnmarshalBinary(data []byte) error {
return e.p.UnmarshalBinary(data)
}

func (s *ristrettoScalar) String() string { return fmt.Sprintf("0x%x", s.s.Bytes()) }
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Do we need this?

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Yes.

func (s *ristrettoScalar) SetUint64(n uint64) { s.s.SetUint64(n) }

func (s *ristrettoScalar) IsEqual(x Scalar) bool {
Expand Down
22 changes: 16 additions & 6 deletions group/short.go
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Expand Up @@ -30,7 +30,7 @@ func (g wG) String() string { return g.c.Params().Name }
func (g wG) NewElement() Element { return g.zeroElement() }
func (g wG) NewScalar() Scalar { return g.zeroScalar() }
func (g wG) Identity() Element { return g.zeroElement() }
func (g wG) zeroScalar() *wScl { return &wScl{g, nil} }
func (g wG) zeroScalar() *wScl { return &wScl{g, make([]byte, (g.c.Params().BitSize+7)/8)} }
func (g wG) zeroElement() *wElt { return &wElt{g, new(big.Int), new(big.Int)} }
func (g wG) Generator() Element { return &wElt{g, g.c.Params().Gx, g.c.Params().Gy} }
func (g wG) Order() Scalar { s := &wScl{g, nil}; s.fromBig(g.c.Params().N); return s }
Expand All @@ -44,6 +44,15 @@ func (g wG) RandomScalar(rd io.Reader) Scalar {
mustReadFull(rd, b)
return g.HashToScalar(b, nil)
}
func (g wG) RandomNonZeroScalar(rd io.Reader) Scalar {
zero := g.zeroScalar()
for {
s := g.RandomScalar(rd)
if !s.IsEqual(zero) {
return s
}
}
}
func (g wG) cvtElt(e Element) *wElt {
if e == nil {
return g.zeroElement()
Expand Down Expand Up @@ -202,35 +211,36 @@ func (s *wScl) IsEqual(a Scalar) bool {
return subtle.ConstantTimeCompare(s.k, aa.k) == 1
}
func (s *wScl) fromBig(b *big.Int) {
if err := s.UnmarshalBinary(b.Bytes()); err != nil {
k := new(big.Int).Mod(b, s.c.Params().N)
if err := s.UnmarshalBinary(k.Bytes()); err != nil {
panic(err)
}
}
func (s *wScl) Add(a, b Scalar) Scalar {
aa, bb := s.cvtScl(a), s.cvtScl(b)
r := new(big.Int)
r.SetBytes(aa.k).Add(r, new(big.Int).SetBytes(bb.k)).Mod(r, s.c.Params().N)
r.SetBytes(aa.k).Add(r, new(big.Int).SetBytes(bb.k))
s.fromBig(r)
return s
}
func (s *wScl) Sub(a, b Scalar) Scalar {
aa, bb := s.cvtScl(a), s.cvtScl(b)
r := new(big.Int)
r.SetBytes(aa.k).Sub(r, new(big.Int).SetBytes(bb.k)).Mod(r, s.c.Params().N)
r.SetBytes(aa.k).Sub(r, new(big.Int).SetBytes(bb.k))
s.fromBig(r)
return s
}
func (s *wScl) Mul(a, b Scalar) Scalar {
aa, bb := s.cvtScl(a), s.cvtScl(b)
r := new(big.Int)
r.SetBytes(aa.k).Mul(r, new(big.Int).SetBytes(bb.k)).Mod(r, s.c.Params().N)
r.SetBytes(aa.k).Mul(r, new(big.Int).SetBytes(bb.k))
s.fromBig(r)
return s
}
func (s *wScl) Neg(a Scalar) Scalar {
aa := s.cvtScl(a)
r := new(big.Int)
r.SetBytes(aa.k).Neg(r).Mod(r, s.c.Params().N)
r.SetBytes(aa.k).Neg(r)
s.fromBig(r)
return s
}
Expand Down