From 2c505efd1ec03dc28ebabbb54253f3eb9e719be5 Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Mon, 2 Mar 2015 15:26:24 +0100
Subject: p2p/discover: add NodeID.Pubkey

---
 p2p/discover/node.go | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

(limited to 'p2p/discover/node.go')

diff --git a/p2p/discover/node.go b/p2p/discover/node.go
index c6d2e9766..de2588258 100644
--- a/p2p/discover/node.go
+++ b/p2p/discover/node.go
@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math/big"
 	"math/rand"
 	"net"
 	"net/url"
@@ -14,6 +15,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/crypto/secp256k1"
 	"github.com/ethereum/go-ethereum/rlp"
 )
@@ -187,6 +189,19 @@ func PubkeyID(pub *ecdsa.PublicKey) NodeID {
 	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) {
-- 
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