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// Package ecc implements a generic interface for ECDH, ECDSA, and EdDSA.
package ecc
import (
"bytes"
"crypto/subtle"
"io"
"github.com/ProtonMail/go-crypto/openpgp/errors"
ed448lib "github.com/cloudflare/circl/sign/ed448"
)
type ed448 struct{}
func NewEd448() *ed448 {
return &ed448{}
}
func (c *ed448) GetCurveName() string {
return "ed448"
}
// MarshalBytePoint encodes the public point from native format, adding the prefix.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-5.5.5.5
func (c *ed448) MarshalBytePoint(x []byte) []byte {
// Return prefixed
return append([]byte{0x40}, x...)
}
// UnmarshalBytePoint decodes a point from prefixed format to native.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-5.5.5.5
func (c *ed448) UnmarshalBytePoint(point []byte) (x []byte) {
if len(point) != ed448lib.PublicKeySize+1 {
return nil
}
// Strip prefix
return point[1:]
}
// MarshalByteSecret encoded a scalar from native format to prefixed.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-5.5.5.5
func (c *ed448) MarshalByteSecret(d []byte) []byte {
// Return prefixed
return append([]byte{0x40}, d...)
}
// UnmarshalByteSecret decodes a scalar from prefixed format to native.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-5.5.5.5
func (c *ed448) UnmarshalByteSecret(s []byte) (d []byte) {
// Check prefixed size
if len(s) != ed448lib.SeedSize+1 {
return nil
}
// Strip prefix
return s[1:]
}
// MarshalSignature splits a signature in R and S, where R is in prefixed native format and
// S is an MPI with value zero.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-5.2.3.3.2
func (c *ed448) MarshalSignature(sig []byte) (r, s []byte) {
return append([]byte{0x40}, sig...), []byte{}
}
// UnmarshalSignature decodes R and S in the native format. Only R is used, in prefixed native format.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-5.2.3.3.2
func (c *ed448) UnmarshalSignature(r, s []byte) (sig []byte) {
if len(r) != ed448lib.SignatureSize+1 {
return nil
}
return r[1:]
}
func (c *ed448) GenerateEdDSA(rand io.Reader) (pub, priv []byte, err error) {
pk, sk, err := ed448lib.GenerateKey(rand)
if err != nil {
return nil, nil, err
}
return pk, sk[:ed448lib.SeedSize], nil
}
func getEd448Sk(publicKey, privateKey []byte) ed448lib.PrivateKey {
privateKeyCap, privateKeyLen, publicKeyLen := cap(privateKey), len(privateKey), len(publicKey)
if privateKeyCap >= privateKeyLen+publicKeyLen &&
bytes.Equal(privateKey[privateKeyLen:privateKeyLen+publicKeyLen], publicKey) {
return privateKey[:privateKeyLen+publicKeyLen]
}
return append(privateKey[:privateKeyLen:privateKeyLen], publicKey...)
}
func (c *ed448) Sign(publicKey, privateKey, message []byte) (sig []byte, err error) {
// Ed448 is used with the empty string as a context string.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-13.7
sig = ed448lib.Sign(getEd448Sk(publicKey, privateKey), message, "")
return sig, nil
}
func (c *ed448) Verify(publicKey, message, sig []byte) bool {
// Ed448 is used with the empty string as a context string.
// See https://datatracker.ietf.org/doc/html/draft-ietf-openpgp-crypto-refresh-06#section-13.7
return ed448lib.Verify(publicKey, message, sig, "")
}
func (c *ed448) ValidateEdDSA(publicKey, privateKey []byte) (err error) {
priv := getEd448Sk(publicKey, privateKey)
expectedPriv := ed448lib.NewKeyFromSeed(priv.Seed())
if subtle.ConstantTimeCompare(priv, expectedPriv) == 0 {
return errors.KeyInvalidError("ecc: invalid ed448 secret")
}
return nil
}
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