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// Package ecc implements a generic interface for ECDH, ECDSA, and EdDSA.
package ecc
import (
"crypto/ecdsa"
"crypto/elliptic"
"fmt"
"github.com/ProtonMail/go-crypto/openpgp/errors"
"io"
"math/big"
)
type genericCurve struct {
Curve elliptic.Curve
}
func NewGenericCurve(c elliptic.Curve) *genericCurve {
return &genericCurve{
Curve: c,
}
}
func (c *genericCurve) GetCurveName() string {
return c.Curve.Params().Name
}
func (c *genericCurve) MarshalBytePoint(point []byte) []byte {
return point
}
func (c *genericCurve) UnmarshalBytePoint(point []byte) []byte {
return point
}
func (c *genericCurve) MarshalIntegerPoint(x, y *big.Int) []byte {
return elliptic.Marshal(c.Curve, x, y)
}
func (c *genericCurve) UnmarshalIntegerPoint(point []byte) (x, y *big.Int) {
return elliptic.Unmarshal(c.Curve, point)
}
func (c *genericCurve) MarshalByteSecret(d []byte) []byte {
return d
}
func (c *genericCurve) UnmarshalByteSecret(d []byte) []byte {
return d
}
func (c *genericCurve) MarshalIntegerSecret(d *big.Int) []byte {
return d.Bytes()
}
func (c *genericCurve) UnmarshalIntegerSecret(d []byte) *big.Int {
return new(big.Int).SetBytes(d)
}
func (c *genericCurve) GenerateECDH(rand io.Reader) (point, secret []byte, err error) {
secret, x, y, err := elliptic.GenerateKey(c.Curve, rand)
if err != nil {
return nil, nil, err
}
point = elliptic.Marshal(c.Curve, x, y)
return point, secret, nil
}
func (c *genericCurve) GenerateECDSA(rand io.Reader) (x, y, secret *big.Int, err error) {
priv, err := ecdsa.GenerateKey(c.Curve, rand)
if err != nil {
return
}
return priv.X, priv.Y, priv.D, nil
}
func (c *genericCurve) Encaps(rand io.Reader, point []byte) (ephemeral, sharedSecret []byte, err error) {
xP, yP := elliptic.Unmarshal(c.Curve, point)
if xP == nil {
panic("invalid point")
}
d, x, y, err := elliptic.GenerateKey(c.Curve, rand)
if err != nil {
return nil, nil, err
}
vsG := elliptic.Marshal(c.Curve, x, y)
zbBig, _ := c.Curve.ScalarMult(xP, yP, d)
byteLen := (c.Curve.Params().BitSize + 7) >> 3
zb := make([]byte, byteLen)
zbBytes := zbBig.Bytes()
copy(zb[byteLen-len(zbBytes):], zbBytes)
return vsG, zb, nil
}
func (c *genericCurve) Decaps(ephemeral, secret []byte) (sharedSecret []byte, err error) {
x, y := elliptic.Unmarshal(c.Curve, ephemeral)
zbBig, _ := c.Curve.ScalarMult(x, y, secret)
byteLen := (c.Curve.Params().BitSize + 7) >> 3
zb := make([]byte, byteLen)
zbBytes := zbBig.Bytes()
copy(zb[byteLen-len(zbBytes):], zbBytes)
return zb, nil
}
func (c *genericCurve) Sign(rand io.Reader, x, y, d *big.Int, hash []byte) (r, s *big.Int, err error) {
priv := &ecdsa.PrivateKey{D: d, PublicKey: ecdsa.PublicKey{X: x, Y: y, Curve: c.Curve}}
return ecdsa.Sign(rand, priv, hash)
}
func (c *genericCurve) Verify(x, y *big.Int, hash []byte, r, s *big.Int) bool {
pub := &ecdsa.PublicKey{X: x, Y: y, Curve: c.Curve}
return ecdsa.Verify(pub, hash, r, s)
}
func (c *genericCurve) validate(xP, yP *big.Int, secret []byte) error {
// the public point should not be at infinity (0,0)
zero := new(big.Int)
if xP.Cmp(zero) == 0 && yP.Cmp(zero) == 0 {
return errors.KeyInvalidError(fmt.Sprintf("ecc (%s): infinity point", c.Curve.Params().Name))
}
// re-derive the public point Q' = (X,Y) = dG
// to compare to declared Q in public key
expectedX, expectedY := c.Curve.ScalarBaseMult(secret)
if xP.Cmp(expectedX) != 0 || yP.Cmp(expectedY) != 0 {
return errors.KeyInvalidError(fmt.Sprintf("ecc (%s): invalid point", c.Curve.Params().Name))
}
return nil
}
func (c *genericCurve) ValidateECDSA(xP, yP *big.Int, secret []byte) error {
return c.validate(xP, yP, secret)
}
func (c *genericCurve) ValidateECDH(point []byte, secret []byte) error {
xP, yP := elliptic.Unmarshal(c.Curve, point)
if xP == nil {
return errors.KeyInvalidError(fmt.Sprintf("ecc (%s): invalid point", c.Curve.Params().Name))
}
return c.validate(xP, yP, secret)
}
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