Add support for Ed25519

go.mod

@@ -5,4 +5,5 @@ go 1.12
 require (
 	github.com/emersion/go-milter v0.0.0-20190311184326-c3095a41a6fe
 	github.com/emersion/go-msgauth v0.0.0-20190307192406-8646172ce7a5
+	golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2
 )

query.go

@@ -5,9 +5,12 @@ import (
 	"crypto/rsa"
 	"crypto/x509"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"net"
 	"strings"
+
+	"golang.org/x/crypto/ed25519"
 )
 
 type verifier interface {
@@ -19,14 +22,29 @@ type rsaVerifier struct {
 	*rsa.PublicKey
 }
 
-func (v *rsaVerifier) Public() crypto.PublicKey {
+func (v rsaVerifier) Public() crypto.PublicKey {
 	return v.PublicKey
 }
 
-func (v *rsaVerifier) Verify(hash crypto.Hash, hashed, sig []byte) error {
+func (v rsaVerifier) Verify(hash crypto.Hash, hashed, sig []byte) error {
 	return rsa.VerifyPKCS1v15(v.PublicKey, hash, hashed, sig)
 }
 
+type ed25519Verifier struct {
+	ed25519.PublicKey
+}
+
+func (v ed25519Verifier) Public() crypto.PublicKey {
+	return v.PublicKey
+}
+
+func (v ed25519Verifier) Verify(hash crypto.Hash, hashed, sig []byte) error {
+	if !ed25519.Verify(v.PublicKey, hashed, sig) {
+		return errors.New("dkim: invalid Ed25519 signature")
+	}
+	return nil
+}
+
 type queryResult struct {
 	Verifier  verifier
 	KeyAlgo   string
@@ -102,8 +120,15 @@ func parsePublicKey(s string) (*queryResult, error) {
 		if rsaPub.Size() * 8 < 1024 {
 			return nil, permFailError(fmt.Sprintf("key is too short: want 1024 bits, has %v bits", rsaPub.Size() * 8))
 		}
-		res.Verifier = &rsaVerifier{rsaPub}
+		res.Verifier = rsaVerifier{rsaPub}
 		res.KeyAlgo = "rsa"
+	case "ed25519":
+		if len(b) != ed25519.PublicKeySize {
+			return nil, permFailError(fmt.Sprintf("invalid Ed25519 public key size: %v", len(b)))
+		}
+		ed25519Pub := ed25519.PublicKey(b)
+		res.Verifier = ed25519Verifier{ed25519Pub}
+		res.KeyAlgo = "ed25519"
 	default:
 		return nil, permFailError("unsupported key algorithm")
 	}

sign.go

@@ -12,6 +12,8 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	"golang.org/x/crypto/ed25519"
 )
 
 var randReader io.Reader = rand.Reader
@@ -87,6 +89,8 @@ func Sign(w io.Writer, r io.Reader, options *SignOptions) error {
 	switch options.Signer.Public().(type) {
 	case *rsa.PublicKey:
 		keyAlgo = "rsa"
+	case ed25519.PublicKey:
+		keyAlgo = "ed25519"
 	default:
 		return fmt.Errorf("dkim: unsupported key algorithm %T", options.Signer.Public())
 	}