go-pulse/p2p/discover/node.go
Felix Lange 2adcc31bb4 p2p/discover: new distance metric based on sha3(id)
The previous metric was pubkey1^pubkey2, as specified in the Kademlia
paper. We missed that EC public keys are not uniformly distributed.
Using the hash of the public keys addresses that. It also makes it
a bit harder to generate node IDs that are close to a particular node.
2015-05-06 16:10:41 +02:00

305 lines
7.6 KiB
Go

package discover
import (
"crypto/ecdsa"
"crypto/elliptic"
"encoding/hex"
"errors"
"fmt"
"math/big"
"math/rand"
"net"
"net/url"
"strconv"
"strings"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/crypto/secp256k1"
)
const nodeIDBits = 512
// Node represents a host on the network.
type Node struct {
IP net.IP // len 4 for IPv4 or 16 for IPv6
UDP, TCP uint16 // port numbers
ID NodeID // the node's public key
// This is a cached copy of sha3(ID) which is used for node
// distance calculations. This is part of Node in order to make it
// possible to write tests that need a node at a certain distance.
// In those tests, the content of sha will not actually correspond
// with ID.
sha common.Hash
}
func newNode(id NodeID, ip net.IP, udpPort, tcpPort uint16) *Node {
if ipv4 := ip.To4(); ipv4 != nil {
ip = ipv4
}
return &Node{
IP: ip,
UDP: udpPort,
TCP: tcpPort,
ID: id,
sha: crypto.Sha3Hash(id[:]),
}
}
func (n *Node) addr() *net.UDPAddr {
return &net.UDPAddr{IP: n.IP, Port: int(n.UDP)}
}
// The string representation of a Node is a URL.
// Please see ParseNode for a description of the format.
func (n *Node) String() string {
addr := net.TCPAddr{IP: n.IP, Port: int(n.TCP)}
u := url.URL{
Scheme: "enode",
User: url.User(fmt.Sprintf("%x", n.ID[:])),
Host: addr.String(),
}
if n.UDP != n.TCP {
u.RawQuery = "discport=" + strconv.Itoa(int(n.UDP))
}
return u.String()
}
// ParseNode parses a node URL.
//
// A node URL has scheme "enode".
//
// The hexadecimal node ID is encoded in the username portion of the
// URL, separated from the host by an @ sign. The hostname can only be
// given as an IP address, DNS domain names are not allowed. The port
// in the host name section is the TCP listening port. If the TCP and
// UDP (discovery) ports differ, the UDP port is specified as query
// parameter "discport".
//
// In the following example, the node URL describes
// a node with IP address 10.3.58.6, TCP listening port 30303
// and UDP discovery port 30301.
//
// enode://<hex node id>@10.3.58.6:30303?discport=30301
func ParseNode(rawurl string) (*Node, error) {
var (
id NodeID
ip net.IP
tcpPort, udpPort uint64
)
u, err := url.Parse(rawurl)
if u.Scheme != "enode" {
return nil, errors.New("invalid URL scheme, want \"enode\"")
}
// Parse the Node ID from the user portion.
if u.User == nil {
return nil, errors.New("does not contain node ID")
}
if id, err = HexID(u.User.String()); err != nil {
return nil, fmt.Errorf("invalid node ID (%v)", err)
}
// Parse the IP address.
host, port, err := net.SplitHostPort(u.Host)
if err != nil {
return nil, fmt.Errorf("invalid host: %v", err)
}
if ip = net.ParseIP(host); ip == nil {
return nil, errors.New("invalid IP address")
}
// Ensure the IP is 4 bytes long for IPv4 addresses.
if ipv4 := ip.To4(); ipv4 != nil {
ip = ipv4
}
// Parse the port numbers.
if tcpPort, err = strconv.ParseUint(port, 10, 16); err != nil {
return nil, errors.New("invalid port")
}
udpPort = tcpPort
qv := u.Query()
if qv.Get("discport") != "" {
udpPort, err = strconv.ParseUint(qv.Get("discport"), 10, 16)
if err != nil {
return nil, errors.New("invalid discport in query")
}
}
return newNode(id, ip, uint16(udpPort), uint16(tcpPort)), nil
}
// MustParseNode parses a node URL. It panics if the URL is not valid.
func MustParseNode(rawurl string) *Node {
n, err := ParseNode(rawurl)
if err != nil {
panic("invalid node URL: " + err.Error())
}
return n
}
// NodeID is a unique identifier for each node.
// The node identifier is a marshaled elliptic curve public key.
type NodeID [nodeIDBits / 8]byte
// NodeID prints as a long hexadecimal number.
func (n NodeID) String() string {
return fmt.Sprintf("%x", n[:])
}
// The Go syntax representation of a NodeID is a call to HexID.
func (n NodeID) GoString() string {
return fmt.Sprintf("discover.HexID(\"%x\")", n[:])
}
// HexID converts a hex string to a NodeID.
// The string may be prefixed with 0x.
func HexID(in string) (NodeID, error) {
if strings.HasPrefix(in, "0x") {
in = in[2:]
}
var id NodeID
b, err := hex.DecodeString(in)
if err != nil {
return id, err
} else if len(b) != len(id) {
return id, fmt.Errorf("wrong length, need %d hex bytes", len(id))
}
copy(id[:], b)
return id, nil
}
// MustHexID converts a hex string to a NodeID.
// It panics if the string is not a valid NodeID.
func MustHexID(in string) NodeID {
id, err := HexID(in)
if err != nil {
panic(err)
}
return id
}
// PubkeyID returns a marshaled representation of the given public key.
func PubkeyID(pub *ecdsa.PublicKey) NodeID {
var id NodeID
pbytes := elliptic.Marshal(pub.Curve, pub.X, pub.Y)
if len(pbytes)-1 != len(id) {
panic(fmt.Errorf("need %d bit pubkey, got %d bits", (len(id)+1)*8, len(pbytes)))
}
copy(id[:], pbytes[1:])
return id
}
// Pubkey returns the public key represented by the node ID.
// It returns an error if the ID is not a point on the curve.
func (id NodeID) Pubkey() (*ecdsa.PublicKey, error) {
p := &ecdsa.PublicKey{Curve: crypto.S256(), X: new(big.Int), Y: new(big.Int)}
half := len(id) / 2
p.X.SetBytes(id[:half])
p.Y.SetBytes(id[half:])
if !p.Curve.IsOnCurve(p.X, p.Y) {
return nil, errors.New("not a point on the S256 curve")
}
return p, nil
}
// recoverNodeID computes the public key used to sign the
// given hash from the signature.
func recoverNodeID(hash, sig []byte) (id NodeID, err error) {
pubkey, err := secp256k1.RecoverPubkey(hash, sig)
if err != nil {
return id, err
}
if len(pubkey)-1 != len(id) {
return id, fmt.Errorf("recovered pubkey has %d bits, want %d bits", len(pubkey)*8, (len(id)+1)*8)
}
for i := range id {
id[i] = pubkey[i+1]
}
return id, nil
}
// distcmp compares the distances a->target and b->target.
// Returns -1 if a is closer to target, 1 if b is closer to target
// and 0 if they are equal.
func distcmp(target, a, b common.Hash) int {
for i := range target {
da := a[i] ^ target[i]
db := b[i] ^ target[i]
if da > db {
return 1
} else if da < db {
return -1
}
}
return 0
}
// table of leading zero counts for bytes [0..255]
var lzcount = [256]int{
8, 7, 6, 6, 5, 5, 5, 5,
4, 4, 4, 4, 4, 4, 4, 4,
3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3,
2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0,
}
// logdist returns the logarithmic distance between a and b, log2(a ^ b).
func logdist(a, b common.Hash) int {
lz := 0
for i := range a {
x := a[i] ^ b[i]
if x == 0 {
lz += 8
} else {
lz += lzcount[x]
break
}
}
return len(a)*8 - lz
}
// hashAtDistance returns a random hash such that logdist(a, b) == n
func hashAtDistance(a common.Hash, n int) (b common.Hash) {
if n == 0 {
return a
}
// flip bit at position n, fill the rest with random bits
b = a
pos := len(a) - n/8 - 1
bit := byte(0x01) << (byte(n%8) - 1)
if bit == 0 {
pos++
bit = 0x80
}
b[pos] = a[pos]&^bit | ^a[pos]&bit // TODO: randomize end bits
for i := pos + 1; i < len(a); i++ {
b[i] = byte(rand.Intn(255))
}
return b
}