/
helpers.go
65 lines (54 loc) · 1.32 KB
/
helpers.go
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package schnorrkel
import (
"crypto/rand"
"github.com/gtank/merlin"
r255 "github.com/gtank/ristretto255"
)
func challengeScalar(t *merlin.Transcript, msg []byte) *r255.Scalar {
scb := t.ExtractBytes(msg, 64)
sc := r255.NewScalar()
sc.FromUniformBytes(scb)
return sc
}
// https://github.com/w3f/schnorrkel/blob/718678e51006d84c7d8e4b6cde758906172e74f8/src/scalars.rs#L18
func divideScalarByCofactor(s []byte) []byte {
l := len(s) - 1
low := byte(0)
for i := range s {
r := s[l-i] & 0x07 // remainder
s[l-i] >>= 3
s[l-i] += low
low = r << 5
}
return s
}
// NewRandomElement returns a random ristretto element
func NewRandomElement() (*r255.Element, error) {
e := r255.NewElement()
s := [64]byte{}
_, err := rand.Read(s[:])
if err != nil {
return nil, err
}
return e.FromUniformBytes(s[:]), nil
}
// NewRandomScalar returns a random ristretto scalar
func NewRandomScalar() (*r255.Scalar, error) {
s := [64]byte{}
_, err := rand.Read(s[:])
if err != nil {
return nil, err
}
ss := r255.NewScalar()
return ss.FromUniformBytes(s[:]), nil
}
// ScalarFromBytes returns a ristretto scalar from the input bytes
// performs input mod l where l is the group order
func ScalarFromBytes(b [32]byte) (*r255.Scalar, error) {
s := r255.NewScalar()
err := s.Decode(b[:])
if err != nil {
return nil, err
}
return s, nil
}