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packets.go
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packets.go
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package krach
import (
_ "encoding/binary"
"errors"
"fmt"
_ "fmt"
)
// packetType represents the type of a packet as unsigned 8 bit integer
type packetType uint8
// Byte returns the representation of the packet type as a single byte
func (p packetType) Byte() byte {
return byte(p)
}
func (p packetType) String() string {
switch p {
case packetTypeHandshakeInit:
return "HandshakeInit"
case packetTypeHandshakeInitResponse:
return "HandshakeResponse"
case packetTypeHandshakeFin:
return "HandshakeFin"
case packetTypeTransport:
return "Transport"
default:
return "Invalid"
}
}
// Known packet types are defined here
const (
packetTypeInvalid packetType = 0x00
packetTypeHandshakeInit packetType = 0x01
packetTypeHandshakeInitResponse packetType = 0x02
packetTypeHandshakeFin packetType = 0x03
packetTypeTransport packetType = 0x10
)
type frameCommand uint8
const (
frameCmdSYN frameCommand = 0x01
frameCmdSYNACK frameCommand = 0x02
frameCmdPSH frameCommand = 0x03
frameCmdFIN frameCommand = 0x04
)
func (f frameCommand) Byte() byte {
return byte(f)
}
type handshakeInitPacket struct {
ephemeralKey [32]byte
}
func (h *handshakeInitPacket) PacketType() packetType {
return packetTypeHandshakeInit
}
func (h *handshakeInitPacket) Length() int {
return 32
}
func (h *handshakeInitPacket) Type() packetType {
return packetTypeHandshakeInit
}
func (h *handshakeInitPacket) ReadEPublic() ([32]byte, error) {
return h.ephemeralKey, nil
}
func (h *handshakeInitPacket) ReadEncryptedIdentity() ([]byte, error) {
panic("Handshake Init must not contain an encrypted identitiy")
}
func (h *handshakeInitPacket) ReadPayload() ([]byte, error) {
// panic("Handshake init must not have a generic payload")
return nil, nil
}
func (h *handshakeInitPacket) WriteEPublic(e [32]byte) {
h.ephemeralKey = e
}
func (h *handshakeInitPacket) WriteEncryptedIdentity(s []byte) {
panic("Handshake Init packets can't contain an encrypted identity")
}
func (h *handshakeInitPacket) WriteEncryptedPayload(p []byte) {
// panic("Handshake Init packets can't contain a payload")
// Ignore, we don't want to add payloads to init packets
}
func (h *handshakeInitPacket) Serialize() []byte {
len := 1 /*Version*/ + 1 /*Handshake Type*/ + 2 /*Packet length*/ + 32 /*key length*/
buf := make([]byte, len)
buf[0] = KrachVersion
buf[1] = packetTypeHandshakeInit.Byte()
endianess.PutUint16(buf[2:4], 32 /*key length*/) // Packet length only counts bytes following the packet length
copy(buf[4:], h.ephemeralKey[:])
return buf
}
func (h *handshakeInitPacket) Deserialize(buf []byte) error {
if len(buf) != 32 {
return fmt.Errorf("invalid length of handshake init packet. Expected 32 bytes, but got %d bytes", len(buf))
}
var ek [32]byte
copy(ek[:], buf)
h.ephemeralKey = ek
return nil
}
type handshakeResponsePacket struct {
ephemeralKey [32]byte
smolCertEncrypted []byte
payloadEncrypted []byte
receivedLength int
}
func (h *handshakeResponsePacket) PacketType() packetType {
return packetTypeHandshakeInitResponse
}
func (h *handshakeResponsePacket) Length() int {
return h.receivedLength
}
func (h *handshakeResponsePacket) ReadEPublic() ([32]byte, error) {
return h.ephemeralKey, nil
}
func (h *handshakeResponsePacket) ReadEncryptedIdentity() ([]byte, error) {
return h.smolCertEncrypted, nil
}
func (h *handshakeResponsePacket) ReadPayload() ([]byte, error) {
return h.payloadEncrypted, nil
}
func (h *handshakeResponsePacket) WriteEPublic(e [32]byte) {
h.ephemeralKey = e
}
func (h *handshakeResponsePacket) WriteEncryptedIdentity(s []byte) {
h.smolCertEncrypted = s
}
func (h *handshakeResponsePacket) WriteEncryptedPayload(p []byte) {
h.payloadEncrypted = p
}
func (h *handshakeResponsePacket) Serialize() []byte {
length := 1 /*Packet type*/ + 2 /*Packet length*/ + 32 /*ephemeral key length*/ +
2 /*id length*/ + len(h.smolCertEncrypted) + 2 /*payload length*/ + len(h.payloadEncrypted)
buf := make([]byte, length)
buf[0] = packetTypeHandshakeInitResponse.Byte()
endianess.PutUint16(buf[1:3], uint16(length-3))
copy(buf[3:35], h.ephemeralKey[:])
offset := writeLengthPrefixed(buf[35:], h.smolCertEncrypted) + 35 /* manual offset from ephemeral key */
writeLengthPrefixed(buf[offset:], h.payloadEncrypted)
return buf
}
func (h *handshakeResponsePacket) Deserialize(buf []byte) (err error) {
if len(buf) < 84 /*Minimal possible length*/ {
return fmt.Errorf("invalid packet length for HandshakeResponse packet. Got only %d bytes", len(buf))
}
h.receivedLength = len(buf)
copy(h.ephemeralKey[:], buf[:32])
offset := 32
var nextOffset int
h.smolCertEncrypted, nextOffset, err = readLengthPrefixed(buf[offset:])
if err != nil {
return fmt.Errorf("failed to read encrypted smol cert from handshake response packet: %w", err)
}
offset = offset + nextOffset
h.payloadEncrypted, _, err = readLengthPrefixed(buf[offset:])
return
}
type handshakeFinPacket struct {
smolCertEncrypted []byte
payloadEncrypted []byte
receivedLength int
}
func (h *handshakeFinPacket) PacketType() packetType {
return packetTypeHandshakeFin
}
func (h *handshakeFinPacket) Length() int {
return h.receivedLength
}
func (h *handshakeFinPacket) ReadEPublic() ([32]byte, error) {
panic("HandshakeFin packets do not contain ephemeral public keys")
}
func (h *handshakeFinPacket) ReadEncryptedIdentity() ([]byte, error) {
return h.smolCertEncrypted, nil
}
func (h *handshakeFinPacket) ReadPayload() ([]byte, error) {
return h.payloadEncrypted, nil
}
func (h *handshakeFinPacket) WriteEPublic(e [32]byte) {
panic("HandshakeFin packets can't contain ephemeral public keys")
}
func (h *handshakeFinPacket) WriteEncryptedIdentity(s []byte) {
h.smolCertEncrypted = s
}
func (h *handshakeFinPacket) WriteEncryptedPayload(p []byte) {
h.payloadEncrypted = p
}
func (h *handshakeFinPacket) Serialize() []byte {
length := 1 /*Packet type*/ + 2 /*Packet length*/ +
2 /*id length*/ + len(h.smolCertEncrypted) + 2 /*payload length*/ + len(h.payloadEncrypted)
buf := make([]byte, length)
buf[0] = packetTypeHandshakeFin.Byte()
endianess.PutUint16(buf[1:3], uint16(length-3))
offset := 3
nextOffset := writeLengthPrefixed(buf[offset:], h.smolCertEncrypted)
offset = offset + nextOffset
writeLengthPrefixed(buf[offset:], h.payloadEncrypted)
return buf
}
func (h *handshakeFinPacket) Deserialize(buf []byte) (err error) {
//if len(buf) < 52 {
// return fmt.Errorf("received buffer is too small to contain a Handshake Fin packet. Received only %d bytes", len(buf))
//}
h.receivedLength = len(buf)
offset := 0
h.smolCertEncrypted, offset, err = readLengthPrefixed(buf)
if err != nil {
return fmt.Errorf("failed to read encrypted smol cert from HandshakeFin packet: %w", err)
}
if offset < h.receivedLength {
var payloadOffset int
h.payloadEncrypted, payloadOffset, err = readLengthPrefixed(buf[offset:])
if err != nil {
return fmt.Errorf("failed to read additional payload of HandshakeFin packet: %w", err)
}
offset += payloadOffset
}
// offset should be at the packets end by now. If not we received extranous bytes, which hints at an invalid/incomplete packet
if offset != h.receivedLength {
return fmt.Errorf("extra bytes (%d bytes) at the end of HandshakeFin packet detected", h.receivedLength-offset)
}
return nil
}
// readLengthPrefixed reads a length prefixed payload from the given buffer. It return the read payload,
// the offset after the payload, which was just read and if necessary an error
func readLengthPrefixed(buf []byte) ([]byte, int, error) {
if len(buf) < 2 {
return nil, 0, errors.New("buffer too small to decode length prefixed value, need at least 2 bytes")
}
length := endianess.Uint16(buf[:2])
if len(buf) < int(length+2) {
return nil, 0, fmt.Errorf("got invalid length. Prefixed length (%d bytes) is smaller than remaining buffer (%d bytes)", length, len(buf))
}
return buf[2 : length+2], int(length + 2), nil
}
// writeLengthPrefixed writes the payload into the given buffer by prefixing the payload with an uint16
// representation of the payloads length. Therefore the given buffer must at least have a size of
// payload length + 2. This method return the offset in the given buffer, after the payload
func writeLengthPrefixed(buf []byte, payload []byte) (offset int) {
endianess.PutUint16(buf[:2], uint16(len(payload)))
copy(buf[2:], payload)
return 2 + len(payload)
}
func padPayload(buf []byte) ([]byte, uint8) {
origDataLen := len(buf)
bytesToPad := 16 - (origDataLen % 16) /*always pad to 16 bytes as recommended by the specification of ChaCha2020 */
if bytesToPad == 16 {
// We don't need padding if the payload is already divisible by 16
bytesToPad = 0
}
if origDataLen+bytesToPad > cap(buf) {
newBuf := make([]byte, origDataLen+bytesToPad)
copy(newBuf, buf)
buf = newBuf
}
return buf[:origDataLen+bytesToPad], uint8(bytesToPad)
}
func padPrefixPayload(buf []byte) []byte {
// FIXME padding prefix byte is not taken into account here
if len(buf) == 0 {
return buf
}
prefixedBuf := append([]byte{byte(0x00)}, buf...)
paddedBuf, padLen := padPayload(prefixedBuf)
paddedBuf[0] = padLen
return paddedBuf
}
func unpadPayload(buf []byte) []byte {
if len(buf) < 2 {
return buf
}
paddedBytes := int(buf[0])
return buf[1 : len(buf)-(paddedBytes)]
}