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package derhelpers
import (
"crypto"
"crypto/ed25519"
"crypto/x509/pkix"
"encoding/asn1"
"errors"
)
var errEd25519WrongID = errors.New("incorrect object identifier")
var errEd25519WrongKeyType = errors.New("incorrect key type")
// ed25519OID is the OID for the Ed25519 signature scheme: see
// https://datatracker.ietf.org/doc/draft-ietf-curdle-pkix-04.
var ed25519OID = asn1.ObjectIdentifier{1, 3, 101, 112}
// subjectPublicKeyInfo reflects the ASN.1 object defined in the X.509 standard.
//
// This is defined in crypto/x509 as "publicKeyInfo".
type subjectPublicKeyInfo struct {
Algorithm pkix.AlgorithmIdentifier
PublicKey asn1.BitString
}
// MarshalEd25519PublicKey creates a DER-encoded SubjectPublicKeyInfo for an
// ed25519 public key, as defined in
// https://tools.ietf.org/html/draft-ietf-curdle-pkix-04. This is analogous to
// MarshalPKIXPublicKey in crypto/x509, which doesn't currently support Ed25519.
func MarshalEd25519PublicKey(pk crypto.PublicKey) ([]byte, error) {
pub, ok := pk.(ed25519.PublicKey)
if !ok {
return nil, errEd25519WrongKeyType
}
spki := subjectPublicKeyInfo{
Algorithm: pkix.AlgorithmIdentifier{
Algorithm: ed25519OID,
},
PublicKey: asn1.BitString{
BitLength: len(pub) * 8,
Bytes: pub,
},
}
return asn1.Marshal(spki)
}
// ParseEd25519PublicKey returns the Ed25519 public key encoded by the input.
func ParseEd25519PublicKey(der []byte) (crypto.PublicKey, error) {
var spki subjectPublicKeyInfo
if rest, err := asn1.Unmarshal(der, &spki); err != nil {
return nil, err
} else if len(rest) > 0 {
return nil, errors.New("SubjectPublicKeyInfo too long")
}
if !spki.Algorithm.Algorithm.Equal(ed25519OID) {
return nil, errEd25519WrongID
}
if spki.PublicKey.BitLength != ed25519.PublicKeySize*8 {
return nil, errors.New("SubjectPublicKeyInfo PublicKey length mismatch")
}
return ed25519.PublicKey(spki.PublicKey.Bytes), nil
}
// oneAsymmetricKey reflects the ASN.1 structure for storing private keys in
// https://tools.ietf.org/html/draft-ietf-curdle-pkix-04, excluding the optional
// fields, which we don't use here.
//
// This is identical to pkcs8 in crypto/x509.
type oneAsymmetricKey struct {
Version int
Algorithm pkix.AlgorithmIdentifier
PrivateKey []byte
}
// curvePrivateKey is the innter type of the PrivateKey field of
// oneAsymmetricKey.
type curvePrivateKey []byte
// MarshalEd25519PrivateKey returns a DER encoding of the input private key as
// specified in https://tools.ietf.org/html/draft-ietf-curdle-pkix-04.
func MarshalEd25519PrivateKey(sk crypto.PrivateKey) ([]byte, error) {
priv, ok := sk.(ed25519.PrivateKey)
if !ok {
return nil, errEd25519WrongKeyType
}
// Marshal the innter CurvePrivateKey.
curvePrivateKey, err := asn1.Marshal(priv.Seed())
if err != nil {
return nil, err
}
// Marshal the OneAsymmetricKey.
asym := oneAsymmetricKey{
Version: 0,
Algorithm: pkix.AlgorithmIdentifier{
Algorithm: ed25519OID,
},
PrivateKey: curvePrivateKey,
}
return asn1.Marshal(asym)
}
// ParseEd25519PrivateKey returns the Ed25519 private key encoded by the input.
func ParseEd25519PrivateKey(der []byte) (crypto.PrivateKey, error) {
asym := new(oneAsymmetricKey)
if rest, err := asn1.Unmarshal(der, asym); err != nil {
return nil, err
} else if len(rest) > 0 {
return nil, errors.New("OneAsymmetricKey too long")
}
// Check that the key type is correct.
if !asym.Algorithm.Algorithm.Equal(ed25519OID) {
return nil, errEd25519WrongID
}
// Unmarshal the inner CurvePrivateKey.
seed := new(curvePrivateKey)
if rest, err := asn1.Unmarshal(asym.PrivateKey, seed); err != nil {
return nil, err
} else if len(rest) > 0 {
return nil, errors.New("CurvePrivateKey too long")
}
return ed25519.NewKeyFromSeed(*seed), nil
}
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