/
minnow.go
222 lines (185 loc) · 4.47 KB
/
minnow.go
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// Minnow is a winnow and chaff implementation in Go.
//
// See: http://people.csail.mit.edu/rivest/Chaffing.txt
package minnow
import (
"crypto/hmac"
"crypto/sha512"
"encoding/binary"
"errors"
"hash"
"io"
"log"
cryptoRand "crypto/rand"
mathRand "math/rand"
)
var (
ErrAlreadyClosed = errors.New("Writer has already been closed")
ErrMaxLengthExceeded = errors.New("Maximum message length (1<<64 - 1) exceeded")
NumChaff = 200 //FIXME Randomize?
)
type Packet struct {
Header PacketHeader
Payload []byte
}
type PacketHeader struct {
SequenceN uint32
Mac [64]byte
Size uint32
}
type WriteCloser struct {
closed bool
hash hash.Hash
message []byte
destination io.WriteCloser
numchaff int
}
func NewWriteCloser(secret []byte, w io.WriteCloser) *WriteCloser {
return &WriteCloser{
closed: false,
hash: hmac.New(sha512.New, secret),
message: make([]byte, 0),
destination: w,
numchaff: NumChaff,
}
}
// Writes a message fragment to the internal buffer
// Return value is always (len(m), nil)
func (mw *WriteCloser) Write(m []byte) (int, error) {
mw.message = append(mw.message, m...)
return len(m), nil
}
// Close is when we actually get the end of the message and can write it
func (mw *WriteCloser) Close() error {
if !mw.closed {
defer mw.destination.Close()
log.Printf("Writing message:\n%s", string(mw.message))
mw.closed = true
for p := range sequentialPacketChannel(mw.message, mw.hash) {
packets := make([]Packet, mw.numchaff+1)
packets[0] = *p
for i := 1; i < mw.numchaff+1; i++ {
packets[i] = makeFakeMessage(1, p.Header.SequenceN)
}
packets = randomizePackets(packets)
for _, p := range packets {
mw.writePacket(&p)
}
}
return mw.destination.Close()
}
return ErrAlreadyClosed
}
func (mw *WriteCloser) writePacket(packet *Packet) error {
log.Printf("Writing packet: #%d - %+v\n", packet.Header.SequenceN, packet.Payload)
err := binary.Write(mw.destination, binary.BigEndian, packet.Header)
if err != nil {
return err
}
_, err = mw.destination.Write(packet.Payload)
if err != nil {
return err
}
return nil
}
type Reader struct {
hash hash.Hash
message []byte
reader io.Reader
closed bool
}
func NewReader(secret []byte, r io.Reader) *Reader {
return &Reader{
hash: hmac.New(sha512.New, secret),
message: make([]byte, 0),
reader: r,
closed: false,
}
}
func (r *Reader) ReadAll() []byte {
for {
res := new(PacketHeader)
err := binary.Read(r.reader, binary.BigEndian, res)
if err != nil {
if err != io.EOF {
// Probably shouldn't Fatal on this...
log.Fatalf("Received an error reading header: %s\n", err)
}
r.closed = true
break
}
d := make([]byte, res.Size)
_, err = io.ReadFull(r.reader, d)
if err != nil {
if err != io.EOF {
log.Fatalf("Received error reading message body: %s\n", err)
}
r.closed = true
break
}
if r.matches(d, res.Mac) {
r.message = append(r.message, d...)
}
}
return r.message
}
func (r *Reader) matches(data []byte, provided [64]byte) bool {
r.hash.Write(data)
defer r.hash.Reset()
m := r.hash.Sum(nil)
var mbuf [64]byte
for i, _ := range mbuf {
mbuf[i] = m[i]
}
return mbuf == provided
}
// Send len(data) # of sequential packets, hashed with the provided hash.Hash
// down the provided channel
func sequentialPacketChannel(data []byte, hasher hash.Hash) chan *Packet {
// FIXME: Packet size is hard-coded at 1
outchan := make(chan *Packet)
go func() {
for i, _ := range data {
var mbuf [64]byte
hasher.Write(data[i : i+1])
m := hasher.Sum(nil)
for i, _ := range mbuf {
mbuf[i] = m[i]
}
hasher.Reset()
h := PacketHeader{
SequenceN: uint32(i),
Mac: mbuf,
Size: uint32(1),
}
outchan <- &Packet{h, data[i : i+1]}
}
close(outchan)
}()
return outchan
}
func randomizePackets(packets []Packet) []Packet {
newpackets := make([]Packet, 0)
for len(packets) > 0 {
randndx := mathRand.Intn(len(packets))
newpackets = append(newpackets, packets[randndx])
packets = append(packets[:randndx], packets[randndx+1:]...)
}
return newpackets
}
func makeFakeMessage(size uint32, sequencenum uint32) Packet {
crypthash := make([]byte, 64)
hash := new([64]byte)
payloadbuf := make([]byte, size)
cryptoRand.Read(payloadbuf)
cryptoRand.Read(crypthash)
for i, v := range crypthash {
hash[i] = v
}
ph := PacketHeader{
SequenceN: sequencenum,
Mac: *hash,
Size: size,
}
return Packet{ph, payloadbuf}
}