lnd.xprv/elkrem/serdes.go

198 lines
5.4 KiB
Go

package elkrem
import (
"bytes"
"encoding/binary"
"fmt"
"github.com/btcsuite/btcd/wire"
)
/* Serialization and Deserialization methods for the Elkrem structs.
Senders turn into 41 byte long slices. Receivers are variable length,
with 41 bytes for each stored hash, up to a maximum of 64. Receivers are
prepended with the total number of hashes, so the total max size is 2625 bytes.
*/
// ToBytes turns the Elkrem Sender into a 41 byte slice:
// first the tree height (1 byte), then 8 byte index of last sent,
// then the 32 byte root sha hash.
func (e *ElkremSender) ToBytes() ([]byte, error) {
var buf bytes.Buffer
// write 1 byte height of tree (size of the whole sender)
err := binary.Write(&buf, binary.BigEndian, e.treeHeight)
if err != nil {
return nil, err
}
// write 8 byte index of current sha (last sent)
err = binary.Write(&buf, binary.BigEndian, e.current)
if err != nil {
return nil, err
}
// write 32 byte sha hash
n, err := buf.Write(e.root.Bytes())
if err != nil {
return nil, err
}
if n != 32 {
return nil, fmt.Errorf("%d byte hash, expect 32", n)
}
return buf.Bytes(), nil
}
// ElkremSenderFromBytes turns a 41 byte slice into a sender, picking up at
// the index where it left off.
func ElkremSenderFromBytes(b []byte) (ElkremSender, error) {
var e ElkremSender
buf := bytes.NewBuffer(b)
// read 1 byte height
err := binary.Read(buf, binary.BigEndian, &e.treeHeight)
if err != nil {
return e, err
}
// read 8 byte index
err = binary.Read(buf, binary.BigEndian, &e.current)
if err != nil {
return e, err
}
// read 32 byte sha root
err = e.root.SetBytes(buf.Next(32))
if err != nil {
return e, err
}
if e.treeHeight < 1 || e.treeHeight > 63 { // check for super high / low tree
return e, fmt.Errorf("Read invalid sender tree height %d", e.treeHeight)
}
for j := uint8(0); j <= e.treeHeight; j++ {
e.maxIndex = e.maxIndex<<1 | 1
}
e.maxIndex--
if e.current > e.maxIndex { // check for index higher than height allows
return e, fmt.Errorf("Sender claims current %d; %d max with height %d",
e.current, e.maxIndex, e.treeHeight)
}
return e, nil
}
// ToBytes turns the Elkrem Receiver into a bunch of bytes in a slice.
// first the tree height (1 byte), then number of nodes (1 byte),
// then a series of 41 byte long serialized nodes,
// which are 1 byte height, 8 byte index, 32 byte hash.
func (e *ElkremReceiver) ToBytes() ([]byte, error) {
numOfNodes := uint8(len(e.s))
if numOfNodes == 0 {
return nil, fmt.Errorf("Can't serialize empty ElkremReceiver")
}
if numOfNodes > 64 {
return nil, fmt.Errorf("Broken ElkremReceiver has %d nodes, max 64",
len(e.s))
}
var buf bytes.Buffer // create buffer
// write tree height (1 byte)
err := binary.Write(&buf, binary.BigEndian, e.treeHeight)
if err != nil {
return nil, err
}
// write number of nodes (1 byte)
err = binary.Write(&buf, binary.BigEndian, numOfNodes)
if err != nil {
return nil, err
}
for _, node := range e.s {
// write 1 byte height
err = binary.Write(&buf, binary.BigEndian, node.h)
if err != nil {
return nil, err
}
// write 8 byte index
err = binary.Write(&buf, binary.BigEndian, node.i)
if err != nil {
return nil, err
}
// write 32 byte sha hash
n, err := buf.Write(node.sha.Bytes())
if err != nil {
return nil, err
}
if n != 32 { // make sure that was 32 bytes
return nil, fmt.Errorf("%d byte hash, expect 32", n)
}
}
if buf.Len() != (int(numOfNodes)*41)+2 {
return nil, fmt.Errorf("Somehow made wrong size buf, got %d expect %d",
buf.Len(), (numOfNodes*41)+2)
}
return buf.Bytes(), nil
}
func ElkremReceiverFromBytes(b []byte) (ElkremReceiver, error) {
var e ElkremReceiver
var numOfNodes uint8
buf := bytes.NewBuffer(b)
// read 1 byte tree height
err := binary.Read(buf, binary.BigEndian, &e.treeHeight)
if err != nil {
return e, err
}
if e.treeHeight < 1 || e.treeHeight > 63 {
return e, fmt.Errorf("Read invalid receiver height: %d", e.treeHeight)
}
var max uint64 // maximum possible given height
for j := uint8(0); j <= e.treeHeight; j++ {
max = max<<1 | 1
}
max--
// read 1 byte number of nodes stored in receiver
err = binary.Read(buf, binary.BigEndian, &numOfNodes)
if err != nil {
return e, err
}
if numOfNodes < 1 || numOfNodes > 64 {
return e, fmt.Errorf("Read invalid number of nodes: %d", numOfNodes)
}
if buf.Len() != (int(numOfNodes)*41)+2 {
return e, fmt.Errorf("Input buf wrong size, expect %d got %d",
(numOfNodes*41)+2, buf.Len())
}
for i := uint8(0); i < numOfNodes; i++ {
var node ElkremNode
node.sha = new(wire.ShaHash)
// read 1 byte height
err := binary.Read(buf, binary.BigEndian, &node.h)
if err != nil {
return e, err
}
// read 8 byte index
err = binary.Read(buf, binary.BigEndian, &node.i)
if err != nil {
return e, err
}
// read 32 byte sha hash
err = node.sha.SetBytes(buf.Next(32))
if err != nil {
return e, err
}
// sanity check. Note that this doesn't check that index and height
// match. Could add that but it's slow.
if node.h > 63 { // check for super high nodes
return e, fmt.Errorf("Read invalid node height %d", node.h)
}
if node.i > max { // check for index higher than height allows
return e, fmt.Errorf("Node claims index %d; %d max at height %d",
node.i, max, node.h)
}
e.s = append(e.s, node)
if i > 0 { // check that node heights are descending
if e.s[i-1].h < e.s[i].h {
return e, fmt.Errorf("Node heights out of order")
}
}
}
return e, nil
}