Fix Issue #6

party.FromBytes now returns an error if the length of the given byte slice is too small

Author: adr1anh

pkg/eddsa/secret_share.go

@@ -58,13 +58,16 @@ func (sk *SecretShare) MarshalBinary() ([]byte, error) {
 
 // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
 func (sk *SecretShare) UnmarshalBinary(data []byte) error {
+	var err error
 	if len(data) != party.ByteSize+32 {
 		return errors.New("SecretShare: data is not the right size")
 	}
-	sk.ID = party.FromBytes(data)
+	if sk.ID, err = party.FromBytes(data); err != nil {
+		return err
+	}
 	data = data[party.ByteSize:]
-	_, err := sk.Secret.SetCanonicalBytes(data)
-	if err != nil {
+
+	if _, err = sk.Secret.SetCanonicalBytes(data); err != nil {
 		return err
 	}
 	sk.Public.ScalarBaseMult(&sk.Secret)

pkg/frost/party/id.go

@@ -58,8 +58,12 @@ func (p ID) String() string {
 }
 
 // FromBytes reads the first party.ByteSize bytes from b and creates an ID from it.
-func FromBytes(b []byte) ID {
-	return ID(binary.BigEndian.Uint16(b))
+// Returns an error if b is too small to hold an ID.
+func FromBytes(b []byte) (ID, error) {
+	if len(b) < ByteSize {
+		return 0, errors.New("party.FromBytes: b is not long enough to hold an ID")
+	}
+	return ID(binary.BigEndian.Uint16(b)), nil
 }
 
 // RandIDn returns, as an ID, a non-negative pseudo-random number in [1,n]

pkg/internal/polynomial/exponent.go

@@ -163,7 +163,11 @@ func (p *Exponent) MarshalBinary() (data []byte, err error) {
 
 // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
 func (p *Exponent) UnmarshalBinary(data []byte) error {
-	coefficientCount := party.FromBytes(data) + 1
+	degree, err := party.FromBytes(data)
+	if err != nil {
+		return err
+	}
+	coefficientCount := degree + 1
 	remaining := data[party.ByteSize:]
 
 	count := len(remaining)

pkg/messages/messages.go

@@ -91,13 +91,24 @@ func (m *Message) MarshalBinary() ([]byte, error) {
 
 // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface.
 func (m *Message) UnmarshalBinary(data []byte) error {
+	var err error
+	// ensure the length is long enough to hold the header
+	// 1 byte for message type + 2*party.ByteSize for from/to
+	if len(data) < 1+2*party.ByteSize {
+		return errors.New("data does not contain header")
+	}
+
 	msgType := MessageType(data[0])
 	m.messageType = msgType
 	data = data[1:]
-	m.from = party.FromBytes(data)
+	if m.from, err = party.FromBytes(data); err != nil {
+		return err
+	}
 	data = data[party.ByteSize:]
 
-	m.to = party.FromBytes(data)
+	if m.to, err = party.FromBytes(data); err != nil {
+		return err
+	}
 	data = data[party.ByteSize:]
 
 	switch msgType {