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group: add SetUint64 method to Group.Scalar. #301

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Merged
merged 1 commit into from
Nov 4, 2021
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group: add SetUint64 method to Group.Scalar. #301

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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 @@ -45,6 +45,7 @@ type Element interface {
// Scalar represents an integer scalar.
type Scalar interface {
IsEqual(Scalar) bool
SetUint64(uint64)
Add(Scalar, Scalar) Scalar
Sub(Scalar, Scalar) Scalar
Mul(Scalar, Scalar) Scalar
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11 changes: 11 additions & 0 deletions group/group_test.go
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Expand Up @@ -183,18 +183,22 @@ func testScalar(t *testing.T, testTimes int, g group.Group) {
d := g.NewScalar()
e := g.NewScalar()
f := g.NewScalar()
one := g.NewScalar()
one.SetUint64(1)
params := g.Params()
for i := 0; i < testTimes; i++ {
a := g.RandomScalar(rand.Reader)
b := g.RandomScalar(rand.Reader)
c.Add(a, b)
d.Sub(a, b)
e.Mul(c, d)
e.Add(e, one)

c.Mul(a, a)
d.Mul(b, b)
d.Neg(d)
f.Add(c, d)
f.Add(f, one)
enc1, err1 := e.MarshalBinary()
enc2, err2 := f.MarshalBinary()
if err1 != nil || err2 != nil || !bytes.Equal(enc1, enc2) {
Expand All @@ -204,6 +208,13 @@ func testScalar(t *testing.T, testTimes int, g group.Group) {
test.ReportError(t, l, params.ScalarLength)
}
}

a := g.RandomScalar(rand.Reader)
c.Inv(a)
c.Mul(c, a)
if !one.IsEqual(c) {
test.ReportError(t, c, one, a)
}
}

func BenchmarkElement(b *testing.B) {
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3 changes: 3 additions & 0 deletions group/ristretto255.go
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Expand Up @@ -4,6 +4,7 @@ import (
"crypto"
_ "crypto/sha512" // to link libraries
"io"
"math/big"

r255 "github.com/bwesterb/go-ristretto"
)
Expand Down Expand Up @@ -145,6 +146,8 @@ func (e *ristrettoElement) UnmarshalBinary(data []byte) error {
return e.p.UnmarshalBinary(data)
}

func (s *ristrettoScalar) SetUint64(n uint64) { s.s.SetBigInt(new(big.Int).SetUint64(n)) }
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Better to use SetBytes. Scalars are encoded little endian, so simply write the uint64 into the [32]byte at the first 8 bytes using encoding/binary.LittleEndian.

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I can also add a SetUint64.


func (s *ristrettoScalar) IsEqual(x Scalar) bool {
return s.s.Equals(&x.(*ristrettoScalar).s)
}
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3 changes: 2 additions & 1 deletion group/short.go
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Expand Up @@ -195,7 +195,8 @@ type wScl struct {
k []byte
}

func (s *wScl) String() string { return fmt.Sprintf("0x%x", s.k) }
func (s *wScl) String() string { return fmt.Sprintf("0x%x", s.k) }
func (s *wScl) SetUint64(n uint64) { s.fromBig(new(big.Int).SetUint64(n)) }
func (s *wScl) IsEqual(a Scalar) bool {
aa := s.cvtScl(a)
return subtle.ConstantTimeCompare(s.k, aa.k) == 1
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