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armfazharmfazh
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Add sampling of non-zero scalars.
1 parent 48c4180 commit a909bcf

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5 files changed

+38
-17
lines changed

5 files changed

+38
-17
lines changed

‎go.mod

+2-2
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,6 @@ go 1.15
44

55
require (
66
github.com/bwesterb/go-ristretto v1.2.1
7-
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519
8-
golang.org/x/sys v0.0.0-20211007075335-d3039528d8ac
7+
golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871
8+
golang.org/x/sys v0.0.0-20211124211545-fe61309f8881
99
)

‎go.sum

+7-8
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,13 @@
1-
github.com/bwesterb/go-ristretto v1.2.0 h1:xxWOVbN5m8NNKiSDZXE1jtZvZnC6JSJ9cYFADiZcWtw=
2-
github.com/bwesterb/go-ristretto v1.2.0/go.mod h1:fUIoIZaG73pV5biE2Blr2xEzDoMj7NFEuV9ekS419A0=
31
github.com/bwesterb/go-ristretto v1.2.1 h1:Xd9ZXmjKE2aY8Ub7+4bX7tXsIPsV1pIZaUlJUjI1toE=
42
github.com/bwesterb/go-ristretto v1.2.1/go.mod h1:fUIoIZaG73pV5biE2Blr2xEzDoMj7NFEuV9ekS419A0=
5-
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519 h1:7I4JAnoQBe7ZtJcBaYHi5UtiO8tQHbUSXxL+pnGRANg=
6-
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
7-
golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
3+
golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871 h1:/pEO3GD/ABYAjuakUS6xSEmmlyVS4kxBNkeA9tLJiTI=
4+
golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
5+
golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
86
golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
7+
golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
98
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
10-
golang.org/x/sys v0.0.0-20211007075335-d3039528d8ac h1:oN6lz7iLW/YC7un8pq+9bOLyXrprv2+DKfkJY+2LJJw=
11-
golang.org/x/sys v0.0.0-20211007075335-d3039528d8ac/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
9+
golang.org/x/sys v0.0.0-20211124211545-fe61309f8881 h1:TyHqChC80pFkXWraUUf6RuB5IqFdQieMLwwCJokV2pc=
10+
golang.org/x/sys v0.0.0-20211124211545-fe61309f8881/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
1211
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
13-
golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
12+
golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
1413
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=

‎group/group.go

+1
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,7 @@ type Group interface {
2323
Order() Scalar
2424
RandomElement(io.Reader) Element
2525
RandomScalar(io.Reader) Scalar
26+
RandomNonZeroScalar(io.Reader) Scalar
2627
HashToElement(data, dst []byte) Element
2728
HashToElementNonUniform(b, dst []byte) Element
2829
HashToScalar(data, dst []byte) Scalar

‎group/ristretto255.go

+12-1
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,7 @@ package group
33
import (
44
"crypto"
55
_ "crypto/sha512" // to link libraries
6+
"fmt"
67
"io"
78

89
r255 "github.com/bwesterb/go-ristretto"
@@ -75,13 +76,22 @@ func (g ristrettoGroup) RandomElement(r io.Reader) Element {
7576
}
7677
}
7778

78-
func (g ristrettoGroup) RandomScalar(r io.Reader) Scalar {
79+
func (g ristrettoGroup) RandomScalar(io.Reader) Scalar {
7980
var x r255.Scalar
8081
x.Rand()
8182
return &ristrettoScalar{
8283
s: x,
8384
}
8485
}
86+
func (g ristrettoGroup) RandomNonZeroScalar(io.Reader) Scalar {
87+
var s r255.Scalar
88+
for {
89+
s.Rand()
90+
if s.IsNonZeroI() == 1 {
91+
return &ristrettoScalar{s}
92+
}
93+
}
94+
}
8595
func (g ristrettoGroup) HashToElementNonUniform(b, dst []byte) Element {
8696
return g.HashToElement(b, dst)
8797
}
@@ -145,6 +155,7 @@ func (e *ristrettoElement) UnmarshalBinary(data []byte) error {
145155
return e.p.UnmarshalBinary(data)
146156
}
147157

158+
func (s *ristrettoScalar) String() string { return fmt.Sprintf("0x%x", s.s.Bytes()) }
148159
func (s *ristrettoScalar) SetUint64(n uint64) { s.s.SetUint64(n) }
149160

150161
func (s *ristrettoScalar) IsEqual(x Scalar) bool {

‎group/short.go

+16-6
Original file line numberDiff line numberDiff line change
@@ -30,7 +30,7 @@ func (g wG) String() string { return g.c.Params().Name }
3030
func (g wG) NewElement() Element { return g.zeroElement() }
3131
func (g wG) NewScalar() Scalar { return g.zeroScalar() }
3232
func (g wG) Identity() Element { return g.zeroElement() }
33-
func (g wG) zeroScalar() *wScl { return &wScl{g, nil} }
33+
func (g wG) zeroScalar() *wScl { return &wScl{g, make([]byte, (g.c.Params().BitSize+7)/8)} }
3434
func (g wG) zeroElement() *wElt { return &wElt{g, new(big.Int), new(big.Int)} }
3535
func (g wG) Generator() Element { return &wElt{g, g.c.Params().Gx, g.c.Params().Gy} }
3636
func (g wG) Order() Scalar { s := &wScl{g, nil}; s.fromBig(g.c.Params().N); return s }
@@ -44,6 +44,15 @@ func (g wG) RandomScalar(rd io.Reader) Scalar {
4444
mustReadFull(rd, b)
4545
return g.HashToScalar(b, nil)
4646
}
47+
func (g wG) RandomNonZeroScalar(rd io.Reader) Scalar {
48+
zero := g.zeroScalar()
49+
for {
50+
s := g.RandomScalar(rd)
51+
if !s.IsEqual(zero) {
52+
return s
53+
}
54+
}
55+
}
4756
func (g wG) cvtElt(e Element) *wElt {
4857
if e == nil {
4958
return g.zeroElement()
@@ -202,35 +211,36 @@ func (s *wScl) IsEqual(a Scalar) bool {
202211
return subtle.ConstantTimeCompare(s.k, aa.k) == 1
203212
}
204213
func (s *wScl) fromBig(b *big.Int) {
205-
if err := s.UnmarshalBinary(b.Bytes()); err != nil {
214+
k := new(big.Int).Mod(b, s.c.Params().N)
215+
if err := s.UnmarshalBinary(k.Bytes()); err != nil {
206216
panic(err)
207217
}
208218
}
209219
func (s *wScl) Add(a, b Scalar) Scalar {
210220
aa, bb := s.cvtScl(a), s.cvtScl(b)
211221
r := new(big.Int)
212-
r.SetBytes(aa.k).Add(r, new(big.Int).SetBytes(bb.k)).Mod(r, s.c.Params().N)
222+
r.SetBytes(aa.k).Add(r, new(big.Int).SetBytes(bb.k))
213223
s.fromBig(r)
214224
return s
215225
}
216226
func (s *wScl) Sub(a, b Scalar) Scalar {
217227
aa, bb := s.cvtScl(a), s.cvtScl(b)
218228
r := new(big.Int)
219-
r.SetBytes(aa.k).Sub(r, new(big.Int).SetBytes(bb.k)).Mod(r, s.c.Params().N)
229+
r.SetBytes(aa.k).Sub(r, new(big.Int).SetBytes(bb.k))
220230
s.fromBig(r)
221231
return s
222232
}
223233
func (s *wScl) Mul(a, b Scalar) Scalar {
224234
aa, bb := s.cvtScl(a), s.cvtScl(b)
225235
r := new(big.Int)
226-
r.SetBytes(aa.k).Mul(r, new(big.Int).SetBytes(bb.k)).Mod(r, s.c.Params().N)
236+
r.SetBytes(aa.k).Mul(r, new(big.Int).SetBytes(bb.k))
227237
s.fromBig(r)
228238
return s
229239
}
230240
func (s *wScl) Neg(a Scalar) Scalar {
231241
aa := s.cvtScl(a)
232242
r := new(big.Int)
233-
r.SetBytes(aa.k).Neg(r).Mod(r, s.c.Params().N)
243+
r.SetBytes(aa.k).Neg(r)
234244
s.fromBig(r)
235245
return s
236246
}

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