crypto/ipa/common/common.go

package common

import (
	"fmt"
	"io"

	"github.com/luxfi/crypto/ipa/bandersnatch/fr"
	"github.com/luxfi/crypto/ipa/banderwagon"
)

// VectorLength is the number of elements in the vector. This value is fixed.
// Note that this means that the degree of the polynomial is one less than this value.
const VectorLength = 256

// PowersOf returns powers of x from 0 to degree-1: <1, x, x^2, ..., x^(degree-1)>.
// Used for polynomial evaluation and computing challenge powers in IPA proofs.
func PowersOf(x fr.Element, degree int) []fr.Element {
	result := make([]fr.Element, degree)
	result[0] = fr.One()

	for i := 1; i < degree; i++ {
		result[i].Mul(&result[i-1], &x)
	}

	return result
}

func ReadPoint(r io.Reader) (*banderwagon.Element, error) {
	var x = make([]byte, 32)
	if _, err := io.ReadAtLeast(r, x, 32); err != nil {
		return nil, fmt.Errorf("reading x coordinate: %w", err)
	}
	var p = &banderwagon.Element{}
	if err := p.SetBytes(x); err != nil {
		return nil, fmt.Errorf("deserializing point: %w", err)
	}
	return p, nil
}

func ReadScalar(r io.Reader) (*fr.Element, error) {
	var x = make([]byte, 32)
	if _, err := io.ReadAtLeast(r, x, 32); err != nil {
		return nil, fmt.Errorf("reading scalar: %w", err)
	}
	var scalar = &fr.Element{}
	if _, err := scalar.SetBytesLECanonical(x); err != nil {
		return nil, fmt.Errorf("deserializing scalar: %s", err)
	}

	return scalar, nil
}