utils.go

package spake

import (
	"crypto/sha256"
	"encoding/base64"
	"errors"

	"github.com/bwesterb/go-ristretto"
)

// deriveBytes hashes arbitrary input into a fixed 32-byte value,
// suitable for conversion into a Ristretto scalar.
func deriveBytes(b []byte) *[32]byte {
	result := sha256.Sum256(b)
	return &result
}

// pointFromBase64 decodes a base64-encoded Ristretto point and validates it
// before returning the corresponding curve point.
func pointFromBase64(s string) (ristretto.Point, error) {
	var P ristretto.Point

	raw, err := base64.StdEncoding.DecodeString(s)
	if err != nil {
		return P, err
	}
	if len(raw) != 32 {
		return P, errors.New("invalid ristretto point length")
	}
	var buf [32]byte
	copy(buf[:], raw)
	if ok := P.SetBytes(&buf); !ok {
		return P, errors.New("could not load ristretto point")
	}
	return P, nil
}

// boolToByte converts a boolean value into a single byte (0 or 1)
// for compact protocol serialization.
func boolToByte(b bool) byte {
	if b {
		return 1
	} else {
		return 0
	}
}

// byteToBool converts a single byte into a boolean value,
// treating any non-zero value as true.
func byteToBool(b byte) bool {
	return b != 0
}

// GetRandomPoint generates a random Ristretto point and returns it
// encoded in base64 format, suitable for testing or parameter generation.
func GetRandomPoint() string {
	var p ristretto.Point
	p.Rand()
	return base64.StdEncoding.EncodeToString(p.Bytes())
}