feature/signature (#4)

* signing messages

* updated, added errors

* using uint32

client/client.go

@@ -2,9 +2,14 @@
 package client
 
 import (
+	"crypto/ecdsa"
+	"crypto/sha256"
+	"encoding/binary"
 	"log"
 
+	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/golang/protobuf/proto"
+	"github.com/pkg/errors"
 	"github.com/vacp2p/dasy/protobuf"
 	mvds "github.com/vacp2p/mvds/node"
 	mvdsproto "github.com/vacp2p/mvds/protobuf"
@@ -23,6 +28,8 @@ type Client struct {
 	node  mvds.Node
 	store store.MessageStore // @todo we probably need a different message store, not sure tho
 
+	identity *ecdsa.PrivateKey
+
 	lastMessage state.MessageID // @todo maybe make type
 }
 
@@ -64,16 +71,19 @@ func (c *Client) send(chat Chat, t protobuf.Message_MessageType, body []byte) er
 		PreviousMessage: c.lastMessage[:],
 	}
 
-	// @todo sign
+	err := c.sign(msg)
+	if err != nil {
+		return errors.Wrap(err, "failed to sign message")
+	}
 
 	buf, err := proto.Marshal(msg)
 	if err != nil {
-		return err
+		return errors.Wrap(err, "failed to marshall message")
 	}
 
 	id, err := c.node.AppendMessage(state.GroupID(chat), buf)
 	if err != nil {
-		return err
+		return errors.Wrap(err, "failed to append message")
 	}
 
 	c.lastMessage = id
@@ -111,3 +121,21 @@ func (c *Client) handlePreviousMessage(group state.GroupID, previousMessage stat
 		log.Printf("error while requesting message: %s", err.Error())
 	}
 }
+
+// sign signs generates a signature of the message and adds it to the message.
+func (c *Client) sign(m *protobuf.Message) error {
+	b := make([]byte, 4)
+	binary.LittleEndian.PutUint32(b, uint32(m.MessageType))
+	b = append(b, m.Body...)
+	b = append(b, m.PreviousMessage...)
+
+	hash := sha256.Sum256(b)
+
+	sig, err := crypto.Sign(hash[:], c.identity)
+	if err != nil {
+		return err
+	}
+
+	m.Signature = sig
+	return nil
+}

protobuf/message.pb.go

@@ -61,7 +61,7 @@ type Message struct {
 	MessageType          Message_MessageType `protobuf:"varint,1,opt,name=message_type,json=messageType,proto3,enum=mvds.Message_MessageType" json:"message_type,omitempty"`
 	Body                 []byte              `protobuf:"bytes,2,opt,name=body,proto3" json:"body,omitempty"`
 	PreviousMessage      []byte              `protobuf:"bytes,3,opt,name=previous_message,json=previousMessage,proto3" json:"previous_message,omitempty"`
-	Signature            [][]byte            `protobuf:"bytes,4,rep,name=signature,proto3" json:"signature,omitempty"`
+	Signature            []byte              `protobuf:"bytes,4,opt,name=signature,proto3" json:"signature,omitempty"`
 	XXX_NoUnkeyedLiteral struct{}            `json:"-"`
 	XXX_unrecognized     []byte              `json:"-"`
 	XXX_sizecache        int32               `json:"-"`
@@ -113,7 +113,7 @@ func (m *Message) GetPreviousMessage() []byte {
 	return nil
 }
 
-func (m *Message) GetSignature() [][]byte {
+func (m *Message) GetSignature() []byte {
 	if m != nil {
 		return m.Signature
 	}
@@ -128,7 +128,7 @@ func init() {
 func init() { proto.RegisterFile("protobuf/message.proto", fileDescriptor_8368f5d77b0b9b7b) }
 
 var fileDescriptor_8368f5d77b0b9b7b = []byte{
-	// 231 bytes of a gzipped FileDescriptorProto
+	// 228 bytes of a gzipped FileDescriptorProto
 	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xe2, 0x12, 0x2b, 0x28, 0xca, 0x2f,
 	0xc9, 0x4f, 0x2a, 0x4d, 0xd3, 0xcf, 0x4d, 0x2d, 0x2e, 0x4e, 0x4c, 0x4f, 0xd5, 0x03, 0x0b, 0x08,
 	0xb1, 0xe4, 0x96, 0xa5, 0x14, 0x2b, 0x7d, 0x64, 0xe4, 0x62, 0xf7, 0x85, 0x88, 0x0b, 0xd9, 0x70,
@@ -137,11 +137,11 @@ var fileDescriptor_8368f5d77b0b9b7b = []byte{
 	0x47, 0x48, 0x88, 0x8b, 0x25, 0x29, 0x3f, 0xa5, 0x52, 0x82, 0x49, 0x81, 0x51, 0x83, 0x27, 0x08,
 	0xcc, 0x16, 0xd2, 0xe4, 0x12, 0x28, 0x28, 0x4a, 0x2d, 0xcb, 0xcc, 0x2f, 0x2d, 0x8e, 0x87, 0xaa,
 	0x95, 0x60, 0x06, 0xcb, 0xf3, 0xc3, 0xc4, 0x61, 0x96, 0xcb, 0x70, 0x71, 0x16, 0x67, 0xa6, 0xe7,
-	0x25, 0x96, 0x94, 0x16, 0xa5, 0x4a, 0xb0, 0x28, 0x30, 0x6b, 0xf0, 0x04, 0x21, 0x04, 0x94, 0xbc,
-	0xb9, 0xb8, 0x91, 0x2c, 0x16, 0xe2, 0xe2, 0x62, 0xf3, 0xf4, 0x0b, 0xf3, 0x0c, 0x71, 0x15, 0x60,
-	0x10, 0xe2, 0xe0, 0x62, 0xf1, 0xf2, 0xf7, 0xf4, 0x13, 0x60, 0x14, 0xe2, 0xe4, 0x62, 0xf5, 0x71,
-	0x75, 0x0c, 0x73, 0x15, 0x60, 0x02, 0x09, 0x7a, 0x7b, 0x3a, 0x7b, 0x0b, 0x30, 0x0b, 0xb1, 0x73,
-	0x31, 0x3b, 0x3a, 0x7b, 0x0b, 0xb0, 0x80, 0x84, 0x02, 0xfc, 0x83, 0x43, 0x04, 0x58, 0x9d, 0xb8,
-	0xa2, 0x38, 0x60, 0x61, 0x92, 0xc4, 0x06, 0x66, 0x19, 0x03, 0x02, 0x00, 0x00, 0xff, 0xff, 0x5c,
-	0xd7, 0xa3, 0xb8, 0x26, 0x01, 0x00, 0x00,
+	0x25, 0x96, 0x94, 0x16, 0xa5, 0x4a, 0xb0, 0x80, 0xd5, 0x20, 0x04, 0x94, 0xbc, 0xb9, 0xb8, 0x91,
+	0x2c, 0x16, 0xe2, 0xe2, 0x62, 0xf3, 0xf4, 0x0b, 0xf3, 0x0c, 0x71, 0x15, 0x60, 0x10, 0xe2, 0xe0,
+	0x62, 0xf1, 0xf2, 0xf7, 0xf4, 0x13, 0x60, 0x14, 0xe2, 0xe4, 0x62, 0xf5, 0x71, 0x75, 0x0c, 0x73,
+	0x15, 0x60, 0x02, 0x09, 0x7a, 0x7b, 0x3a, 0x7b, 0x0b, 0x30, 0x0b, 0xb1, 0x73, 0x31, 0x3b, 0x3a,
+	0x7b, 0x0b, 0xb0, 0x80, 0x84, 0x02, 0xfc, 0x83, 0x43, 0x04, 0x58, 0x9d, 0xb8, 0xa2, 0x38, 0x60,
+	0x61, 0x92, 0xc4, 0x06, 0x66, 0x19, 0x03, 0x02, 0x00, 0x00, 0xff, 0xff, 0x41, 0x70, 0xaf, 0x4e,
+	0x26, 0x01, 0x00, 0x00,
 }

protobuf/message.proto

@@ -17,5 +17,5 @@ message Message {
     MessageType message_type = 1;
     bytes body = 2;
     bytes previous_message = 3;
-    repeated bytes signature = 4;
+    bytes signature = 4;
 }