Add config.KnownNotations and check critical notations

openpgp/packet/config.go

@@ -94,6 +94,10 @@ type Config struct {
 	// might be no other way than to tolerate the missing MDC. Setting this flag, allows this
 	// mode of operation. It should be considered a measure of last resort.
 	InsecureAllowUnauthenticatedMessages bool
+	// KnownNotations is a map of Notation Data names to bools, which controls
+	// the notation names that are allowed to be present in critical Notation Data
+	// signature subpackets.
+	KnownNotations map[string]bool
 }
 
 func (c *Config) Random() io.Reader {
@@ -202,3 +206,10 @@ func (c *Config) AllowUnauthenticatedMessages() bool {
 	}
 	return c.InsecureAllowUnauthenticatedMessages
 }
+
+func (c *Config) KnownNotation(notationName string) bool {
+	if c == nil {
+		return false
+	}
+	return c.KnownNotations[notationName]
+}

openpgp/read.go

@@ -515,12 +515,15 @@ func CheckArmoredDetachedSignature(keyring KeyRing, signed, signature io.Reader,
 }
 
 // checkSignatureDetails returns an error if:
+// - The signature (or one of the binding signatures mentioned below)
+//   has a unknown critical notation data subpacket
 // - The primary key of the signing entity is revoked
 // The signature was signed by a subkey and:
 //   - The signing subkey is revoked
 // - The primary identity is revoked
 // - The signature is expired
-// - The primary key of the signing entity is expired according to the primary identity binding signature
+// - The primary key of the signing entity is expired according to the
+//   primary identity binding signature
 // The signature was signed by a subkey and:
 //   - The signing subkey is expired according to the subkey binding signature
 //   - The signing subkey binding signature is expired
@@ -534,20 +537,30 @@ func CheckArmoredDetachedSignature(keyring KeyRing, signed, signature io.Reader,
 func checkSignatureDetails(key *Key, signature *packet.Signature, config *packet.Config) error {
 	now := config.Now()
 	primaryIdentity := key.Entity.PrimaryIdentity()
+	signedBySubKey := key.PublicKey != key.Entity.PrimaryKey
 	sigsToCheck := []*packet.Signature{ signature, primaryIdentity.SelfSignature }
+	if signedBySubKey {
+		sigsToCheck = append(sigsToCheck, key.SelfSignature, key.SelfSignature.EmbeddedSignature)
+	}
+	for _, sig := range sigsToCheck {
+		for _, not := range sig.Notations {
+			if not.IsCritical && !config.KnownNotation(not.Name) {
+				return errors.SignatureError("unknown critical notation: " + not.Name)
+			}
+		}
+	}
 	if key.Entity.Revoked(now) || // primary key is revoked
-		(key.PublicKey != key.Entity.PrimaryKey && key.Revoked(now)) || // subkey is revoked
+		(signedBySubKey && key.Revoked(now)) || // subkey is revoked
 		primaryIdentity.Revoked(now) { // primary identity is revoked
 		return errors.ErrKeyRevoked
 	}
 	if key.Entity.PrimaryKey.KeyExpired(primaryIdentity.SelfSignature, now) { // primary key is expired
 		return errors.ErrKeyExpired
 	}
-	if key.PublicKey != key.Entity.PrimaryKey {
+	if signedBySubKey {
 		if key.PublicKey.KeyExpired(key.SelfSignature, now) { // subkey is expired
 			return errors.ErrKeyExpired
 		}
-		sigsToCheck = append(sigsToCheck, key.SelfSignature, key.SelfSignature.EmbeddedSignature)
 	}
 	for _, sig := range sigsToCheck {
 		if sig.SigExpired(now) { // any of the relevant signatures are expired

openpgp/read_test.go

@@ -435,6 +435,63 @@ func TestDetachedSignatureExpiredCrossSig(t *testing.T) {
 	}
 }
 
+func TestSignatureUnknownNotation(t *testing.T) {
+	el, err := ReadArmoredKeyRing(bytes.NewBufferString(criticalNotationSigner))
+	if err != nil {
+		t.Error(err)
+	}
+	raw, err := armor.Decode(strings.NewReader(signedMessageWithCriticalNotation))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	md, err := ReadMessage(raw.Body, el, nil, nil)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	_, err = ioutil.ReadAll(md.UnverifiedBody)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	const expectedErr string = "openpgp: invalid signature: unknown critical notation: [email protected]"
+	if md.SignatureError == nil || md.SignatureError.Error() != expectedErr {
+		t.Errorf("Expected error '%s', but got error '%s'", expectedErr, md.SignatureError)
+	}
+}
+
+func TestSignatureKnownNotation(t *testing.T) {
+	el, err := ReadArmoredKeyRing(bytes.NewBufferString(criticalNotationSigner))
+	if err != nil {
+		t.Error(err)
+	}
+	raw, err := armor.Decode(strings.NewReader(signedMessageWithCriticalNotation))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	config := &packet.Config{
+		KnownNotations: map[string]bool{
+			"[email protected]": true,
+		},
+	}
+	md, err := ReadMessage(raw.Body, el, nil, config)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	_, err = ioutil.ReadAll(md.UnverifiedBody)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if md.SignatureError != nil {
+		t.Error(md.SignatureError)
+		return
+	}
+}
+
 func TestReadingArmoredPrivateKey(t *testing.T) {
 	el, err := ReadArmoredKeyRing(bytes.NewBufferString(armoredPrivateKeyBlock))
 	if err != nil {

openpgp/read_write_test_data.go

@@ -239,3 +239,36 @@ ITEG9mMgp3TGS9ZzSifMZ8UGtHdp9QdBg8NEVPFzDOMGxpc/Bftav7RRRuPiAER+
 =aQkm
 -----END PGP SIGNATURE-----
 `
+
+const signedMessageWithCriticalNotation = `-----BEGIN PGP MESSAGE-----
+
+owGbwMvMwMH4oOW7S46CznTG09xJDDE3Wl1KUotLuDousDAwcjBYiSmyXL+48d6x
+U1PSGUxcj8IUszKBVMpMaWAAAgEGZpAeh9SKxNyCnFS95PzcytRiBi5OAZjyXXzM
+f8WYLqv7TXP61Sa4rqT12CI3xaN73YS2pt089f96odCKaEPnWJ3iSGmzJaW/ug10
+2Zo8Wj2k4s7t8wt4H3HtTu+y5UZfV3VOO+l//sdE/o+Lsub8FZH7/eOq7OnbNp4n
+vwjE8mqJXetNMfj8r2SCyvkEnlVRYR+/mnge+ib56FdJ8uKtqSxyvgA=
+=fRXs
+-----END PGP MESSAGE-----`
+
+const criticalNotationSigner = `-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=h/aX
+-----END PGP PUBLIC KEY BLOCK-----`