diff --git a/client/internal/sam/datagram.go b/client/internal/sam/datagram.go
index 0c0694a..daece4d 100644
--- a/client/internal/sam/datagram.go
+++ b/client/internal/sam/datagram.go
@@ -5,6 +5,7 @@ import (
 	"io"
 	"strconv"
 	"strings"
+	"time"
 
 	"gosuda.org/ivnp/foundation"
 	"gosuda.org/ivnp/interfaces/destination"
@@ -175,7 +176,7 @@ func (s *samSession) parseReceivedDatagram(delivery networking.StreamingTunnelDe
 		}
 		return foundation.EncodeI2PBase64(packet.V1.From.Bytes()), packet.V1.Payload, true
 	case networking.DatagramProtocolDatagram2:
-		valid, err := packet.V2.VerifyTarget(s.endpoint.Hash())
+		valid, err := packet.V2.VerifyTargetAt(s.endpoint.Hash(), uint32(time.Now().Unix()))
 		if err != nil || !valid || packet.V2.From.Hash() != delivery.From {
 			return "", nil, false
 		}
diff --git a/client/internal/sam/private_destination.go b/client/internal/sam/private_destination.go
index 0a56c7d..fdc0737 100644
--- a/client/internal/sam/private_destination.go
+++ b/client/internal/sam/private_destination.go
@@ -219,11 +219,11 @@ func parseOfflinePrivateKey(identity foundation.Identity, section []byte) (*offl
 		return nil, ErrInvalidKey
 	}
 	offset := 6
-	public := append([]byte(nil), section[offset:offset+publicLength]...)
+	public := section[offset : offset+publicLength]
 	offset += publicLength
-	signature := append([]byte(nil), section[offset:offset+signatureLength]...)
+	signature := section[offset : offset+signatureLength]
 	offset += signatureLength
-	transientPrivate := append([]byte(nil), section[offset:]...)
+	transientPrivate := section[offset:]
 	return &offlinePrivateKey{
 		OfflineSignature: foundation.OfflineSignature{
 			Expires:   binary.BigEndian.Uint32(section[:4]),
diff --git a/client/internal/sam/protocol.go b/client/internal/sam/protocol.go
index 7bcbc3b..5a4a6a2 100644
--- a/client/internal/sam/protocol.go
+++ b/client/internal/sam/protocol.go
@@ -149,6 +149,14 @@ func (s *Server) createSession(ctx context.Context, connection *serverConnection
 	if meta, ok := local.OfflineSignature(); ok {
 		meta := meta
 		offline = &meta
+		if style == styleDatagram {
+			local.ReleaseSensitive()
+			return connection.writeLine("SESSION STATUS RESULT=INVALID_KEY")
+		}
+		if policy.Encrypted {
+			local.ReleaseSensitive()
+			return connection.writeLine("SESSION STATUS RESULT=INVALID_KEY")
+		}
 	}
 	private, err := encodePrivateDestination(local)
 	if err != nil {
diff --git a/foundation/address_generator.go b/foundation/address_generator.go
index 3781a5b..f0226d4 100644
--- a/foundation/address_generator.go
+++ b/foundation/address_generator.go
@@ -305,10 +305,13 @@ func (d *LocalDestination) Sign(message []byte) ([]byte, error) {
 	if d.offline != nil {
 		switch d.offline.keyType {
 		case SigningEdDSASHA512Ed25519:
-			return ed25519.Sign(ed25519.NewKeyFromSeed(d.offline.private), message), nil
+			private := ed25519.NewKeyFromSeed(d.offline.private)
+			defer clear(private)
+			return ed25519.Sign(private, message), nil
 		case SigningRedDSASHA512Ed25519:
 			var private [32]byte
 			copy(private[:], d.offline.private)
+			defer clear(private[:])
 			return Red25519Sign(private, message)
 		default:
 			return nil, ErrEncryptedSigningKey
diff --git a/foundation/offline_signature.go b/foundation/offline_signature.go
index 62b04ff..f62ade0 100644
--- a/foundation/offline_signature.go
+++ b/foundation/offline_signature.go
@@ -18,13 +18,24 @@ type OfflineSignature struct {
 	Signature []byte
 }
 
-// SignedContent returns the authorized content (expires, key type, public key)
-// covered by the offline signature.
+// SignedContentLen returns the encoded length of the authorized content.
+func (o OfflineSignature) SignedContentLen() int { return 6 + len(o.PublicKey) }
+
+// MarshalSignedContentTo serializes the authorized content into dst.
+func (o OfflineSignature) MarshalSignedContentTo(dst []byte) (int, error) {
+	if len(dst) < o.SignedContentLen() {
+		return 0, ErrInvalidIdentity
+	}
+	binary.BigEndian.PutUint32(dst[:4], o.Expires)
+	binary.BigEndian.PutUint16(dst[4:6], uint16(o.Type))
+	copy(dst[6:], o.PublicKey)
+	return o.SignedContentLen(), nil
+}
+
+// SignedContent returns the authorized content (expires, key type, public key).
 func (o OfflineSignature) SignedContent() []byte {
-	signed := make([]byte, 6+len(o.PublicKey))
-	binary.BigEndian.PutUint32(signed[:4], o.Expires)
-	binary.BigEndian.PutUint16(signed[4:6], uint16(o.Type))
-	copy(signed[6:], o.PublicKey)
+	signed := make([]byte, o.SignedContentLen())
+	_, _ = o.MarshalSignedContentTo(signed)
 	return signed
 }