plugeth/p2p/discover/v5wire/encoding_test.go
Felix Lange b628d72766
build: upgrade to go 1.19 (#25726)
This changes the CI / release builds to use the latest Go version. It also
upgrades golangci-lint to a newer version compatible with Go 1.19.

In Go 1.19, godoc has gained official support for links and lists. The
syntax for code blocks in doc comments has changed and now requires a
leading tab character. gofmt adapts comments to the new syntax
automatically, so there are a lot of comment re-formatting changes in this
PR. We need to apply the new format in order to pass the CI lint stage with
Go 1.19.

With the linter upgrade, I have decided to disable 'gosec' - it produces
too many false-positive warnings. The 'deadcode' and 'varcheck' linters
have also been removed because golangci-lint warns about them being
unmaintained. 'unused' provides similar coverage and we already have it
enabled, so we don't lose much with this change.
2022-09-10 13:25:40 +02:00

632 lines
19 KiB
Go

// Copyright 2020 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package v5wire
import (
"bytes"
"crypto/ecdsa"
"encoding/hex"
"errors"
"flag"
"fmt"
"net"
"os"
"path/filepath"
"strings"
"testing"
"github.com/davecgh/go-spew/spew"
"github.com/ethereum/go-ethereum/common/hexutil"
"github.com/ethereum/go-ethereum/common/mclock"
"github.com/ethereum/go-ethereum/crypto"
"github.com/ethereum/go-ethereum/p2p/enode"
)
// To regenerate discv5 test vectors, run
//
// go test -run TestVectors -write-test-vectors
var writeTestVectorsFlag = flag.Bool("write-test-vectors", false, "Overwrite discv5 test vectors in testdata/")
var (
testKeyA, _ = crypto.HexToECDSA("eef77acb6c6a6eebc5b363a475ac583ec7eccdb42b6481424c60f59aa326547f")
testKeyB, _ = crypto.HexToECDSA("66fb62bfbd66b9177a138c1e5cddbe4f7c30c343e94e68df8769459cb1cde628")
testEphKey, _ = crypto.HexToECDSA("0288ef00023598499cb6c940146d050d2b1fb914198c327f76aad590bead68b6")
testIDnonce = [16]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}
)
// This test checks that the minPacketSize and randomPacketMsgSize constants are well-defined.
func TestMinSizes(t *testing.T) {
var (
gcmTagSize = 16
emptyMsg = sizeofMessageAuthData + gcmTagSize
)
t.Log("static header size", sizeofStaticPacketData)
t.Log("whoareyou size", sizeofStaticPacketData+sizeofWhoareyouAuthData)
t.Log("empty msg size", sizeofStaticPacketData+emptyMsg)
if want := emptyMsg; minMessageSize != want {
t.Fatalf("wrong minMessageSize %d, want %d", minMessageSize, want)
}
if sizeofMessageAuthData+randomPacketMsgSize < minMessageSize {
t.Fatalf("randomPacketMsgSize %d too small", randomPacketMsgSize)
}
}
// This test checks the basic handshake flow where A talks to B and A has no secrets.
func TestHandshake(t *testing.T) {
t.Parallel()
net := newHandshakeTest()
defer net.close()
// A -> B RANDOM PACKET
packet, _ := net.nodeA.encode(t, net.nodeB, &Findnode{})
resp := net.nodeB.expectDecode(t, UnknownPacket, packet)
// A <- B WHOAREYOU
challenge := &Whoareyou{
Nonce: resp.(*Unknown).Nonce,
IDNonce: testIDnonce,
RecordSeq: 0,
}
whoareyou, _ := net.nodeB.encode(t, net.nodeA, challenge)
net.nodeA.expectDecode(t, WhoareyouPacket, whoareyou)
// A -> B FINDNODE (handshake packet)
findnode, _ := net.nodeA.encodeWithChallenge(t, net.nodeB, challenge, &Findnode{})
net.nodeB.expectDecode(t, FindnodeMsg, findnode)
if len(net.nodeB.c.sc.handshakes) > 0 {
t.Fatalf("node B didn't remove handshake from challenge map")
}
// A <- B NODES
nodes, _ := net.nodeB.encode(t, net.nodeA, &Nodes{Total: 1})
net.nodeA.expectDecode(t, NodesMsg, nodes)
}
// This test checks that handshake attempts are removed within the timeout.
func TestHandshake_timeout(t *testing.T) {
t.Parallel()
net := newHandshakeTest()
defer net.close()
// A -> B RANDOM PACKET
packet, _ := net.nodeA.encode(t, net.nodeB, &Findnode{})
resp := net.nodeB.expectDecode(t, UnknownPacket, packet)
// A <- B WHOAREYOU
challenge := &Whoareyou{
Nonce: resp.(*Unknown).Nonce,
IDNonce: testIDnonce,
RecordSeq: 0,
}
whoareyou, _ := net.nodeB.encode(t, net.nodeA, challenge)
net.nodeA.expectDecode(t, WhoareyouPacket, whoareyou)
// A -> B FINDNODE (handshake packet) after timeout
net.clock.Run(handshakeTimeout + 1)
findnode, _ := net.nodeA.encodeWithChallenge(t, net.nodeB, challenge, &Findnode{})
net.nodeB.expectDecodeErr(t, errUnexpectedHandshake, findnode)
}
// This test checks handshake behavior when no record is sent in the auth response.
func TestHandshake_norecord(t *testing.T) {
t.Parallel()
net := newHandshakeTest()
defer net.close()
// A -> B RANDOM PACKET
packet, _ := net.nodeA.encode(t, net.nodeB, &Findnode{})
resp := net.nodeB.expectDecode(t, UnknownPacket, packet)
// A <- B WHOAREYOU
nodeA := net.nodeA.n()
if nodeA.Seq() == 0 {
t.Fatal("need non-zero sequence number")
}
challenge := &Whoareyou{
Nonce: resp.(*Unknown).Nonce,
IDNonce: testIDnonce,
RecordSeq: nodeA.Seq(),
Node: nodeA,
}
whoareyou, _ := net.nodeB.encode(t, net.nodeA, challenge)
net.nodeA.expectDecode(t, WhoareyouPacket, whoareyou)
// A -> B FINDNODE
findnode, _ := net.nodeA.encodeWithChallenge(t, net.nodeB, challenge, &Findnode{})
net.nodeB.expectDecode(t, FindnodeMsg, findnode)
// A <- B NODES
nodes, _ := net.nodeB.encode(t, net.nodeA, &Nodes{Total: 1})
net.nodeA.expectDecode(t, NodesMsg, nodes)
}
// In this test, A tries to send FINDNODE with existing secrets but B doesn't know
// anything about A.
func TestHandshake_rekey(t *testing.T) {
t.Parallel()
net := newHandshakeTest()
defer net.close()
session := &session{
readKey: []byte("BBBBBBBBBBBBBBBB"),
writeKey: []byte("AAAAAAAAAAAAAAAA"),
}
net.nodeA.c.sc.storeNewSession(net.nodeB.id(), net.nodeB.addr(), session)
// A -> B FINDNODE (encrypted with zero keys)
findnode, authTag := net.nodeA.encode(t, net.nodeB, &Findnode{})
net.nodeB.expectDecode(t, UnknownPacket, findnode)
// A <- B WHOAREYOU
challenge := &Whoareyou{Nonce: authTag, IDNonce: testIDnonce}
whoareyou, _ := net.nodeB.encode(t, net.nodeA, challenge)
net.nodeA.expectDecode(t, WhoareyouPacket, whoareyou)
// Check that new keys haven't been stored yet.
sa := net.nodeA.c.sc.session(net.nodeB.id(), net.nodeB.addr())
if !bytes.Equal(sa.writeKey, session.writeKey) || !bytes.Equal(sa.readKey, session.readKey) {
t.Fatal("node A stored keys too early")
}
if s := net.nodeB.c.sc.session(net.nodeA.id(), net.nodeA.addr()); s != nil {
t.Fatal("node B stored keys too early")
}
// A -> B FINDNODE encrypted with new keys
findnode, _ = net.nodeA.encodeWithChallenge(t, net.nodeB, challenge, &Findnode{})
net.nodeB.expectDecode(t, FindnodeMsg, findnode)
// A <- B NODES
nodes, _ := net.nodeB.encode(t, net.nodeA, &Nodes{Total: 1})
net.nodeA.expectDecode(t, NodesMsg, nodes)
}
// In this test A and B have different keys before the handshake.
func TestHandshake_rekey2(t *testing.T) {
t.Parallel()
net := newHandshakeTest()
defer net.close()
initKeysA := &session{
readKey: []byte("BBBBBBBBBBBBBBBB"),
writeKey: []byte("AAAAAAAAAAAAAAAA"),
}
initKeysB := &session{
readKey: []byte("CCCCCCCCCCCCCCCC"),
writeKey: []byte("DDDDDDDDDDDDDDDD"),
}
net.nodeA.c.sc.storeNewSession(net.nodeB.id(), net.nodeB.addr(), initKeysA)
net.nodeB.c.sc.storeNewSession(net.nodeA.id(), net.nodeA.addr(), initKeysB)
// A -> B FINDNODE encrypted with initKeysA
findnode, authTag := net.nodeA.encode(t, net.nodeB, &Findnode{Distances: []uint{3}})
net.nodeB.expectDecode(t, UnknownPacket, findnode)
// A <- B WHOAREYOU
challenge := &Whoareyou{Nonce: authTag, IDNonce: testIDnonce}
whoareyou, _ := net.nodeB.encode(t, net.nodeA, challenge)
net.nodeA.expectDecode(t, WhoareyouPacket, whoareyou)
// A -> B FINDNODE (handshake packet)
findnode, _ = net.nodeA.encodeWithChallenge(t, net.nodeB, challenge, &Findnode{})
net.nodeB.expectDecode(t, FindnodeMsg, findnode)
// A <- B NODES
nodes, _ := net.nodeB.encode(t, net.nodeA, &Nodes{Total: 1})
net.nodeA.expectDecode(t, NodesMsg, nodes)
}
func TestHandshake_BadHandshakeAttack(t *testing.T) {
t.Parallel()
net := newHandshakeTest()
defer net.close()
// A -> B RANDOM PACKET
packet, _ := net.nodeA.encode(t, net.nodeB, &Findnode{})
resp := net.nodeB.expectDecode(t, UnknownPacket, packet)
// A <- B WHOAREYOU
challenge := &Whoareyou{
Nonce: resp.(*Unknown).Nonce,
IDNonce: testIDnonce,
RecordSeq: 0,
}
whoareyou, _ := net.nodeB.encode(t, net.nodeA, challenge)
net.nodeA.expectDecode(t, WhoareyouPacket, whoareyou)
// A -> B FINDNODE
incorrect_challenge := &Whoareyou{
IDNonce: [16]byte{5, 6, 7, 8, 9, 6, 11, 12},
RecordSeq: challenge.RecordSeq,
Node: challenge.Node,
sent: challenge.sent,
}
incorrect_findnode, _ := net.nodeA.encodeWithChallenge(t, net.nodeB, incorrect_challenge, &Findnode{})
incorrect_findnode2 := make([]byte, len(incorrect_findnode))
copy(incorrect_findnode2, incorrect_findnode)
net.nodeB.expectDecodeErr(t, errInvalidNonceSig, incorrect_findnode)
// Reject new findnode as previous handshake is now deleted.
net.nodeB.expectDecodeErr(t, errUnexpectedHandshake, incorrect_findnode2)
// The findnode packet is again rejected even with a valid challenge this time.
findnode, _ := net.nodeA.encodeWithChallenge(t, net.nodeB, challenge, &Findnode{})
net.nodeB.expectDecodeErr(t, errUnexpectedHandshake, findnode)
}
// This test checks some malformed packets.
func TestDecodeErrorsV5(t *testing.T) {
t.Parallel()
net := newHandshakeTest()
defer net.close()
net.nodeA.expectDecodeErr(t, errTooShort, []byte{})
// TODO some more tests would be nice :)
// - check invalid authdata sizes
// - check invalid handshake data sizes
}
// This test checks that all test vectors can be decoded.
func TestTestVectorsV5(t *testing.T) {
var (
idA = enode.PubkeyToIDV4(&testKeyA.PublicKey)
idB = enode.PubkeyToIDV4(&testKeyB.PublicKey)
addr = "127.0.0.1"
session = &session{
writeKey: hexutil.MustDecode("0x00000000000000000000000000000000"),
readKey: hexutil.MustDecode("0x01010101010101010101010101010101"),
}
challenge0A, challenge1A, challenge0B Whoareyou
)
// Create challenge packets.
c := Whoareyou{
Nonce: Nonce{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12},
IDNonce: testIDnonce,
}
challenge0A, challenge1A, challenge0B = c, c, c
challenge1A.RecordSeq = 1
net := newHandshakeTest()
challenge0A.Node = net.nodeA.n()
challenge0B.Node = net.nodeB.n()
challenge1A.Node = net.nodeA.n()
net.close()
type testVectorTest struct {
name string // test vector name
packet Packet // the packet to be encoded
challenge *Whoareyou // handshake challenge passed to encoder
prep func(*handshakeTest) // called before encode/decode
}
tests := []testVectorTest{
{
name: "v5.1-whoareyou",
packet: &challenge0B,
},
{
name: "v5.1-ping-message",
packet: &Ping{
ReqID: []byte{0, 0, 0, 1},
ENRSeq: 2,
},
prep: func(net *handshakeTest) {
net.nodeA.c.sc.storeNewSession(idB, addr, session)
net.nodeB.c.sc.storeNewSession(idA, addr, session.keysFlipped())
},
},
{
name: "v5.1-ping-handshake-enr",
packet: &Ping{
ReqID: []byte{0, 0, 0, 1},
ENRSeq: 1,
},
challenge: &challenge0A,
prep: func(net *handshakeTest) {
// Update challenge.Header.AuthData.
net.nodeA.c.Encode(idB, "", &challenge0A, nil)
net.nodeB.c.sc.storeSentHandshake(idA, addr, &challenge0A)
},
},
{
name: "v5.1-ping-handshake",
packet: &Ping{
ReqID: []byte{0, 0, 0, 1},
ENRSeq: 1,
},
challenge: &challenge1A,
prep: func(net *handshakeTest) {
// Update challenge data.
net.nodeA.c.Encode(idB, "", &challenge1A, nil)
net.nodeB.c.sc.storeSentHandshake(idA, addr, &challenge1A)
},
},
}
for _, test := range tests {
test := test
t.Run(test.name, func(t *testing.T) {
net := newHandshakeTest()
defer net.close()
// Override all random inputs.
net.nodeA.c.sc.nonceGen = func(counter uint32) (Nonce, error) {
return Nonce{0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}, nil
}
net.nodeA.c.sc.maskingIVGen = func(buf []byte) error {
return nil // all zero
}
net.nodeA.c.sc.ephemeralKeyGen = func() (*ecdsa.PrivateKey, error) {
return testEphKey, nil
}
// Prime the codec for encoding/decoding.
if test.prep != nil {
test.prep(net)
}
file := filepath.Join("testdata", test.name+".txt")
if *writeTestVectorsFlag {
// Encode the packet.
d, nonce := net.nodeA.encodeWithChallenge(t, net.nodeB, test.challenge, test.packet)
comment := testVectorComment(net, test.packet, test.challenge, nonce)
writeTestVector(file, comment, d)
}
enc := hexFile(file)
net.nodeB.expectDecode(t, test.packet.Kind(), enc)
})
}
}
// testVectorComment creates the commentary for discv5 test vector files.
func testVectorComment(net *handshakeTest, p Packet, challenge *Whoareyou, nonce Nonce) string {
o := new(strings.Builder)
printWhoareyou := func(p *Whoareyou) {
fmt.Fprintf(o, "whoareyou.challenge-data = %#x\n", p.ChallengeData)
fmt.Fprintf(o, "whoareyou.request-nonce = %#x\n", p.Nonce[:])
fmt.Fprintf(o, "whoareyou.id-nonce = %#x\n", p.IDNonce[:])
fmt.Fprintf(o, "whoareyou.enr-seq = %d\n", p.RecordSeq)
}
fmt.Fprintf(o, "src-node-id = %#x\n", net.nodeA.id().Bytes())
fmt.Fprintf(o, "dest-node-id = %#x\n", net.nodeB.id().Bytes())
switch p := p.(type) {
case *Whoareyou:
// WHOAREYOU packet.
printWhoareyou(p)
case *Ping:
fmt.Fprintf(o, "nonce = %#x\n", nonce[:])
fmt.Fprintf(o, "read-key = %#x\n", net.nodeA.c.sc.session(net.nodeB.id(), net.nodeB.addr()).writeKey)
fmt.Fprintf(o, "ping.req-id = %#x\n", p.ReqID)
fmt.Fprintf(o, "ping.enr-seq = %d\n", p.ENRSeq)
if challenge != nil {
// Handshake message packet.
fmt.Fprint(o, "\nhandshake inputs:\n\n")
printWhoareyou(challenge)
fmt.Fprintf(o, "ephemeral-key = %#x\n", testEphKey.D.Bytes())
fmt.Fprintf(o, "ephemeral-pubkey = %#x\n", crypto.CompressPubkey(&testEphKey.PublicKey))
}
default:
panic(fmt.Errorf("unhandled packet type %T", p))
}
return o.String()
}
// This benchmark checks performance of handshake packet decoding.
func BenchmarkV5_DecodeHandshakePingSecp256k1(b *testing.B) {
net := newHandshakeTest()
defer net.close()
var (
idA = net.nodeA.id()
challenge = &Whoareyou{Node: net.nodeB.n()}
message = &Ping{ReqID: []byte("reqid")}
)
enc, _, err := net.nodeA.c.Encode(net.nodeB.id(), "", message, challenge)
if err != nil {
b.Fatal("can't encode handshake packet")
}
challenge.Node = nil // force ENR signature verification in decoder
b.ResetTimer()
input := make([]byte, len(enc))
for i := 0; i < b.N; i++ {
copy(input, enc)
net.nodeB.c.sc.storeSentHandshake(idA, "", challenge)
_, _, _, err := net.nodeB.c.Decode(input, "")
if err != nil {
b.Fatal(err)
}
}
}
// This benchmark checks how long it takes to decode an encrypted ping packet.
func BenchmarkV5_DecodePing(b *testing.B) {
net := newHandshakeTest()
defer net.close()
session := &session{
readKey: []byte{233, 203, 93, 195, 86, 47, 177, 186, 227, 43, 2, 141, 244, 230, 120, 17},
writeKey: []byte{79, 145, 252, 171, 167, 216, 252, 161, 208, 190, 176, 106, 214, 39, 178, 134},
}
net.nodeA.c.sc.storeNewSession(net.nodeB.id(), net.nodeB.addr(), session)
net.nodeB.c.sc.storeNewSession(net.nodeA.id(), net.nodeA.addr(), session.keysFlipped())
addrB := net.nodeA.addr()
ping := &Ping{ReqID: []byte("reqid"), ENRSeq: 5}
enc, _, err := net.nodeA.c.Encode(net.nodeB.id(), addrB, ping, nil)
if err != nil {
b.Fatalf("can't encode: %v", err)
}
b.ResetTimer()
input := make([]byte, len(enc))
for i := 0; i < b.N; i++ {
copy(input, enc)
_, _, packet, _ := net.nodeB.c.Decode(input, addrB)
if _, ok := packet.(*Ping); !ok {
b.Fatalf("wrong packet type %T", packet)
}
}
}
var pp = spew.NewDefaultConfig()
type handshakeTest struct {
nodeA, nodeB handshakeTestNode
clock mclock.Simulated
}
type handshakeTestNode struct {
ln *enode.LocalNode
c *Codec
}
func newHandshakeTest() *handshakeTest {
t := new(handshakeTest)
t.nodeA.init(testKeyA, net.IP{127, 0, 0, 1}, &t.clock)
t.nodeB.init(testKeyB, net.IP{127, 0, 0, 1}, &t.clock)
return t
}
func (t *handshakeTest) close() {
t.nodeA.ln.Database().Close()
t.nodeB.ln.Database().Close()
}
func (n *handshakeTestNode) init(key *ecdsa.PrivateKey, ip net.IP, clock mclock.Clock) {
db, _ := enode.OpenDB("")
n.ln = enode.NewLocalNode(db, key)
n.ln.SetStaticIP(ip)
n.c = NewCodec(n.ln, key, clock)
}
func (n *handshakeTestNode) encode(t testing.TB, to handshakeTestNode, p Packet) ([]byte, Nonce) {
t.Helper()
return n.encodeWithChallenge(t, to, nil, p)
}
func (n *handshakeTestNode) encodeWithChallenge(t testing.TB, to handshakeTestNode, c *Whoareyou, p Packet) ([]byte, Nonce) {
t.Helper()
// Copy challenge and add destination node. This avoids sharing 'c' among the two codecs.
var challenge *Whoareyou
if c != nil {
challengeCopy := *c
challenge = &challengeCopy
challenge.Node = to.n()
}
// Encode to destination.
enc, nonce, err := n.c.Encode(to.id(), to.addr(), p, challenge)
if err != nil {
t.Fatal(fmt.Errorf("(%s) %v", n.ln.ID().TerminalString(), err))
}
t.Logf("(%s) -> (%s) %s\n%s", n.ln.ID().TerminalString(), to.id().TerminalString(), p.Name(), hex.Dump(enc))
return enc, nonce
}
func (n *handshakeTestNode) expectDecode(t *testing.T, ptype byte, p []byte) Packet {
t.Helper()
dec, err := n.decode(p)
if err != nil {
t.Fatal(fmt.Errorf("(%s) %v", n.ln.ID().TerminalString(), err))
}
t.Logf("(%s) %#v", n.ln.ID().TerminalString(), pp.NewFormatter(dec))
if dec.Kind() != ptype {
t.Fatalf("expected packet type %d, got %d", ptype, dec.Kind())
}
return dec
}
func (n *handshakeTestNode) expectDecodeErr(t *testing.T, wantErr error, p []byte) {
t.Helper()
if _, err := n.decode(p); !errors.Is(err, wantErr) {
t.Fatal(fmt.Errorf("(%s) got err %q, want %q", n.ln.ID().TerminalString(), err, wantErr))
}
}
func (n *handshakeTestNode) decode(input []byte) (Packet, error) {
_, _, p, err := n.c.Decode(input, "127.0.0.1")
return p, err
}
func (n *handshakeTestNode) n() *enode.Node {
return n.ln.Node()
}
func (n *handshakeTestNode) addr() string {
return n.ln.Node().IP().String()
}
func (n *handshakeTestNode) id() enode.ID {
return n.ln.ID()
}
// hexFile reads the given file and decodes the hex data contained in it.
// Whitespace and any lines beginning with the # character are ignored.
func hexFile(file string) []byte {
fileContent, err := os.ReadFile(file)
if err != nil {
panic(err)
}
// Gather hex data, ignore comments.
var text []byte
for _, line := range bytes.Split(fileContent, []byte("\n")) {
line = bytes.TrimSpace(line)
if len(line) > 0 && line[0] == '#' {
continue
}
text = append(text, line...)
}
// Parse the hex.
if bytes.HasPrefix(text, []byte("0x")) {
text = text[2:]
}
data := make([]byte, hex.DecodedLen(len(text)))
if _, err := hex.Decode(data, text); err != nil {
panic("invalid hex in " + file)
}
return data
}
// writeTestVector writes a test vector file with the given commentary and binary data.
func writeTestVector(file, comment string, data []byte) {
fd, err := os.OpenFile(file, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
if err != nil {
panic(err)
}
defer fd.Close()
if len(comment) > 0 {
for _, line := range strings.Split(strings.TrimSpace(comment), "\n") {
fmt.Fprintf(fd, "# %s\n", line)
}
fmt.Fprintln(fd)
}
for len(data) > 0 {
var chunk []byte
if len(data) < 32 {
chunk = data
} else {
chunk = data[:32]
}
data = data[len(chunk):]
fmt.Fprintf(fd, "%x\n", chunk)
}
}