peridot/vendor/golang.org/x/crypto/ssh/handshake.go

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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssh
import (
"crypto/rand"
"errors"
"fmt"
"io"
"log"
"net"
"strings"
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"sync"
)
// debugHandshake, if set, prints messages sent and received. Key
// exchange messages are printed as if DH were used, so the debug
// messages are wrong when using ECDH.
const debugHandshake = false
// chanSize sets the amount of buffering SSH connections. This is
// primarily for testing: setting chanSize=0 uncovers deadlocks more
// quickly.
const chanSize = 16
// keyingTransport is a packet based transport that supports key
// changes. It need not be thread-safe. It should pass through
// msgNewKeys in both directions.
type keyingTransport interface {
packetConn
// prepareKeyChange sets up a key change. The key change for a
// direction will be effected if a msgNewKeys message is sent
// or received.
prepareKeyChange(*algorithms, *kexResult) error
// setStrictMode sets the strict KEX mode, notably triggering
// sequence number resets on sending or receiving msgNewKeys.
// If the sequence number is already > 1 when setStrictMode
// is called, an error is returned.
setStrictMode() error
// setInitialKEXDone indicates to the transport that the initial key exchange
// was completed
setInitialKEXDone()
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}
// handshakeTransport implements rekeying on top of a keyingTransport
// and offers a thread-safe writePacket() interface.
type handshakeTransport struct {
conn keyingTransport
config *Config
serverVersion []byte
clientVersion []byte
// hostKeys is non-empty if we are the server. In that case,
// it contains all host keys that can be used to sign the
// connection.
hostKeys []Signer
// publicKeyAuthAlgorithms is non-empty if we are the server. In that case,
// it contains the supported client public key authentication algorithms.
publicKeyAuthAlgorithms []string
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// hostKeyAlgorithms is non-empty if we are the client. In that case,
// we accept these key types from the server as host key.
hostKeyAlgorithms []string
// On read error, incoming is closed, and readError is set.
incoming chan []byte
readError error
mu sync.Mutex
writeError error
sentInitPacket []byte
sentInitMsg *kexInitMsg
pendingPackets [][]byte // Used when a key exchange is in progress.
writePacketsLeft uint32
writeBytesLeft int64
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// If the read loop wants to schedule a kex, it pings this
// channel, and the write loop will send out a kex
// message.
requestKex chan struct{}
// If the other side requests or confirms a kex, its kexInit
// packet is sent here for the write loop to find it.
startKex chan *pendingKex
kexLoopDone chan struct{} // closed (with writeError non-nil) when kexLoop exits
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// data for host key checking
hostKeyCallback HostKeyCallback
dialAddress string
remoteAddr net.Addr
// bannerCallback is non-empty if we are the client and it has been set in
// ClientConfig. In that case it is called during the user authentication
// dance to handle a custom server's message.
bannerCallback BannerCallback
// Algorithms agreed in the last key exchange.
algorithms *algorithms
// Counters exclusively owned by readLoop.
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readPacketsLeft uint32
readBytesLeft int64
// The session ID or nil if first kex did not complete yet.
sessionID []byte
// strictMode indicates if the other side of the handshake indicated
// that we should be following the strict KEX protocol restrictions.
strictMode bool
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}
type pendingKex struct {
otherInit []byte
done chan error
}
func newHandshakeTransport(conn keyingTransport, config *Config, clientVersion, serverVersion []byte) *handshakeTransport {
t := &handshakeTransport{
conn: conn,
serverVersion: serverVersion,
clientVersion: clientVersion,
incoming: make(chan []byte, chanSize),
requestKex: make(chan struct{}, 1),
startKex: make(chan *pendingKex),
kexLoopDone: make(chan struct{}),
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config: config,
}
t.resetReadThresholds()
t.resetWriteThresholds()
// We always start with a mandatory key exchange.
t.requestKex <- struct{}{}
return t
}
func newClientTransport(conn keyingTransport, clientVersion, serverVersion []byte, config *ClientConfig, dialAddr string, addr net.Addr) *handshakeTransport {
t := newHandshakeTransport(conn, &config.Config, clientVersion, serverVersion)
t.dialAddress = dialAddr
t.remoteAddr = addr
t.hostKeyCallback = config.HostKeyCallback
t.bannerCallback = config.BannerCallback
if config.HostKeyAlgorithms != nil {
t.hostKeyAlgorithms = config.HostKeyAlgorithms
} else {
t.hostKeyAlgorithms = supportedHostKeyAlgos
}
go t.readLoop()
go t.kexLoop()
return t
}
func newServerTransport(conn keyingTransport, clientVersion, serverVersion []byte, config *ServerConfig) *handshakeTransport {
t := newHandshakeTransport(conn, &config.Config, clientVersion, serverVersion)
t.hostKeys = config.hostKeys
t.publicKeyAuthAlgorithms = config.PublicKeyAuthAlgorithms
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go t.readLoop()
go t.kexLoop()
return t
}
func (t *handshakeTransport) getSessionID() []byte {
return t.sessionID
}
// waitSession waits for the session to be established. This should be
// the first thing to call after instantiating handshakeTransport.
func (t *handshakeTransport) waitSession() error {
p, err := t.readPacket()
if err != nil {
return err
}
if p[0] != msgNewKeys {
return fmt.Errorf("ssh: first packet should be msgNewKeys")
}
return nil
}
func (t *handshakeTransport) id() string {
if len(t.hostKeys) > 0 {
return "server"
}
return "client"
}
func (t *handshakeTransport) printPacket(p []byte, write bool) {
action := "got"
if write {
action = "sent"
}
if p[0] == msgChannelData || p[0] == msgChannelExtendedData {
log.Printf("%s %s data (packet %d bytes)", t.id(), action, len(p))
} else {
msg, err := decode(p)
log.Printf("%s %s %T %v (%v)", t.id(), action, msg, msg, err)
}
}
func (t *handshakeTransport) readPacket() ([]byte, error) {
p, ok := <-t.incoming
if !ok {
return nil, t.readError
}
return p, nil
}
func (t *handshakeTransport) readLoop() {
first := true
for {
p, err := t.readOnePacket(first)
first = false
if err != nil {
t.readError = err
close(t.incoming)
break
}
// If this is the first kex, and strict KEX mode is enabled,
// we don't ignore any messages, as they may be used to manipulate
// the packet sequence numbers.
if !(t.sessionID == nil && t.strictMode) && (p[0] == msgIgnore || p[0] == msgDebug) {
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continue
}
t.incoming <- p
}
// Stop writers too.
t.recordWriteError(t.readError)
// Unblock the writer should it wait for this.
close(t.startKex)
// Don't close t.requestKex; it's also written to from writePacket.
}
func (t *handshakeTransport) pushPacket(p []byte) error {
if debugHandshake {
t.printPacket(p, true)
}
return t.conn.writePacket(p)
}
func (t *handshakeTransport) getWriteError() error {
t.mu.Lock()
defer t.mu.Unlock()
return t.writeError
}
func (t *handshakeTransport) recordWriteError(err error) {
t.mu.Lock()
defer t.mu.Unlock()
if t.writeError == nil && err != nil {
t.writeError = err
}
}
func (t *handshakeTransport) requestKeyExchange() {
select {
case t.requestKex <- struct{}{}:
default:
// something already requested a kex, so do nothing.
}
}
func (t *handshakeTransport) resetWriteThresholds() {
t.writePacketsLeft = packetRekeyThreshold
if t.config.RekeyThreshold > 0 {
t.writeBytesLeft = int64(t.config.RekeyThreshold)
} else if t.algorithms != nil {
t.writeBytesLeft = t.algorithms.w.rekeyBytes()
} else {
t.writeBytesLeft = 1 << 30
}
}
func (t *handshakeTransport) kexLoop() {
write:
for t.getWriteError() == nil {
var request *pendingKex
var sent bool
for request == nil || !sent {
var ok bool
select {
case request, ok = <-t.startKex:
if !ok {
break write
}
case <-t.requestKex:
break
}
if !sent {
if err := t.sendKexInit(); err != nil {
t.recordWriteError(err)
break
}
sent = true
}
}
if err := t.getWriteError(); err != nil {
if request != nil {
request.done <- err
}
break
}
// We're not servicing t.requestKex, but that is OK:
// we never block on sending to t.requestKex.
// We're not servicing t.startKex, but the remote end
// has just sent us a kexInitMsg, so it can't send
// another key change request, until we close the done
// channel on the pendingKex request.
err := t.enterKeyExchange(request.otherInit)
t.mu.Lock()
t.writeError = err
t.sentInitPacket = nil
t.sentInitMsg = nil
t.resetWriteThresholds()
// we have completed the key exchange. Since the
// reader is still blocked, it is safe to clear out
// the requestKex channel. This avoids the situation
// where: 1) we consumed our own request for the
// initial kex, and 2) the kex from the remote side
// caused another send on the requestKex channel,
clear:
for {
select {
case <-t.requestKex:
//
default:
break clear
}
}
request.done <- t.writeError
// kex finished. Push packets that we received while
// the kex was in progress. Don't look at t.startKex
// and don't increment writtenSinceKex: if we trigger
// another kex while we are still busy with the last
// one, things will become very confusing.
for _, p := range t.pendingPackets {
t.writeError = t.pushPacket(p)
if t.writeError != nil {
break
}
}
t.pendingPackets = t.pendingPackets[:0]
t.mu.Unlock()
}
// Unblock reader.
t.conn.Close()
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// drain startKex channel. We don't service t.requestKex
// because nobody does blocking sends there.
for request := range t.startKex {
request.done <- t.getWriteError()
}
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// Mark that the loop is done so that Close can return.
close(t.kexLoopDone)
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}
// The protocol uses uint32 for packet counters, so we can't let them
// reach 1<<32. We will actually read and write more packets than
// this, though: the other side may send more packets, and after we
// hit this limit on writing we will send a few more packets for the
// key exchange itself.
const packetRekeyThreshold = (1 << 31)
func (t *handshakeTransport) resetReadThresholds() {
t.readPacketsLeft = packetRekeyThreshold
if t.config.RekeyThreshold > 0 {
t.readBytesLeft = int64(t.config.RekeyThreshold)
} else if t.algorithms != nil {
t.readBytesLeft = t.algorithms.r.rekeyBytes()
} else {
t.readBytesLeft = 1 << 30
}
}
func (t *handshakeTransport) readOnePacket(first bool) ([]byte, error) {
p, err := t.conn.readPacket()
if err != nil {
return nil, err
}
if t.readPacketsLeft > 0 {
t.readPacketsLeft--
} else {
t.requestKeyExchange()
}
if t.readBytesLeft > 0 {
t.readBytesLeft -= int64(len(p))
} else {
t.requestKeyExchange()
}
if debugHandshake {
t.printPacket(p, false)
}
if first && p[0] != msgKexInit {
return nil, fmt.Errorf("ssh: first packet should be msgKexInit")
}
if p[0] != msgKexInit {
return p, nil
}
firstKex := t.sessionID == nil
kex := pendingKex{
done: make(chan error, 1),
otherInit: p,
}
t.startKex <- &kex
err = <-kex.done
if debugHandshake {
log.Printf("%s exited key exchange (first %v), err %v", t.id(), firstKex, err)
}
if err != nil {
return nil, err
}
t.resetReadThresholds()
// By default, a key exchange is hidden from higher layers by
// translating it into msgIgnore.
successPacket := []byte{msgIgnore}
if firstKex {
// sendKexInit() for the first kex waits for
// msgNewKeys so the authentication process is
// guaranteed to happen over an encrypted transport.
successPacket = []byte{msgNewKeys}
}
return successPacket, nil
}
const (
kexStrictClient = "kex-strict-c-v00@openssh.com"
kexStrictServer = "kex-strict-s-v00@openssh.com"
)
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// sendKexInit sends a key change message.
func (t *handshakeTransport) sendKexInit() error {
t.mu.Lock()
defer t.mu.Unlock()
if t.sentInitMsg != nil {
// kexInits may be sent either in response to the other side,
// or because our side wants to initiate a key change, so we
// may have already sent a kexInit. In that case, don't send a
// second kexInit.
return nil
}
msg := &kexInitMsg{
CiphersClientServer: t.config.Ciphers,
CiphersServerClient: t.config.Ciphers,
MACsClientServer: t.config.MACs,
MACsServerClient: t.config.MACs,
CompressionClientServer: supportedCompressions,
CompressionServerClient: supportedCompressions,
}
io.ReadFull(rand.Reader, msg.Cookie[:])
// We mutate the KexAlgos slice, in order to add the kex-strict extension algorithm,
// and possibly to add the ext-info extension algorithm. Since the slice may be the
// user owned KeyExchanges, we create our own slice in order to avoid using user
// owned memory by mistake.
msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+2) // room for kex-strict and ext-info
msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...)
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isServer := len(t.hostKeys) > 0
if isServer {
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for _, k := range t.hostKeys {
// If k is a MultiAlgorithmSigner, we restrict the signature
// algorithms. If k is a AlgorithmSigner, presume it supports all
// signature algorithms associated with the key format. If k is not
// an AlgorithmSigner, we can only assume it only supports the
// algorithms that matches the key format. (This means that Sign
// can't pick a different default).
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keyFormat := k.PublicKey().Type()
switch s := k.(type) {
case MultiAlgorithmSigner:
for _, algo := range algorithmsForKeyFormat(keyFormat) {
if contains(s.Algorithms(), underlyingAlgo(algo)) {
msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, algo)
}
}
case AlgorithmSigner:
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msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, algorithmsForKeyFormat(keyFormat)...)
default:
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msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, keyFormat)
}
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}
if t.sessionID == nil {
msg.KexAlgos = append(msg.KexAlgos, kexStrictServer)
}
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} else {
msg.ServerHostKeyAlgos = t.hostKeyAlgorithms
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// As a client we opt in to receiving SSH_MSG_EXT_INFO so we know what
// algorithms the server supports for public key authentication. See RFC
// 8308, Section 2.1.
//
// We also send the strict KEX mode extension algorithm, in order to opt
// into the strict KEX mode.
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if firstKeyExchange := t.sessionID == nil; firstKeyExchange {
msg.KexAlgos = append(msg.KexAlgos, "ext-info-c")
msg.KexAlgos = append(msg.KexAlgos, kexStrictClient)
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}
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}
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packet := Marshal(msg)
// writePacket destroys the contents, so save a copy.
packetCopy := make([]byte, len(packet))
copy(packetCopy, packet)
if err := t.pushPacket(packetCopy); err != nil {
return err
}
t.sentInitMsg = msg
t.sentInitPacket = packet
return nil
}
func (t *handshakeTransport) writePacket(p []byte) error {
switch p[0] {
case msgKexInit:
return errors.New("ssh: only handshakeTransport can send kexInit")
case msgNewKeys:
return errors.New("ssh: only handshakeTransport can send newKeys")
}
t.mu.Lock()
defer t.mu.Unlock()
if t.writeError != nil {
return t.writeError
}
if t.sentInitMsg != nil {
// Copy the packet so the writer can reuse the buffer.
cp := make([]byte, len(p))
copy(cp, p)
t.pendingPackets = append(t.pendingPackets, cp)
return nil
}
if t.writeBytesLeft > 0 {
t.writeBytesLeft -= int64(len(p))
} else {
t.requestKeyExchange()
}
if t.writePacketsLeft > 0 {
t.writePacketsLeft--
} else {
t.requestKeyExchange()
}
if err := t.pushPacket(p); err != nil {
t.writeError = err
}
return nil
}
func (t *handshakeTransport) Close() error {
// Close the connection. This should cause the readLoop goroutine to wake up
// and close t.startKex, which will shut down kexLoop if running.
err := t.conn.Close()
// Wait for the kexLoop goroutine to complete.
// At that point we know that the readLoop goroutine is complete too,
// because kexLoop itself waits for readLoop to close the startKex channel.
<-t.kexLoopDone
return err
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}
func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
if debugHandshake {
log.Printf("%s entered key exchange", t.id())
}
otherInit := &kexInitMsg{}
if err := Unmarshal(otherInitPacket, otherInit); err != nil {
return err
}
magics := handshakeMagics{
clientVersion: t.clientVersion,
serverVersion: t.serverVersion,
clientKexInit: otherInitPacket,
serverKexInit: t.sentInitPacket,
}
clientInit := otherInit
serverInit := t.sentInitMsg
isClient := len(t.hostKeys) == 0
if isClient {
clientInit, serverInit = serverInit, clientInit
magics.clientKexInit = t.sentInitPacket
magics.serverKexInit = otherInitPacket
}
var err error
t.algorithms, err = findAgreedAlgorithms(isClient, clientInit, serverInit)
if err != nil {
return err
}
if t.sessionID == nil && ((isClient && contains(serverInit.KexAlgos, kexStrictServer)) || (!isClient && contains(clientInit.KexAlgos, kexStrictClient))) {
t.strictMode = true
if err := t.conn.setStrictMode(); err != nil {
return err
}
}
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// We don't send FirstKexFollows, but we handle receiving it.
//
// RFC 4253 section 7 defines the kex and the agreement method for
// first_kex_packet_follows. It states that the guessed packet
// should be ignored if the "kex algorithm and/or the host
// key algorithm is guessed wrong (server and client have
// different preferred algorithm), or if any of the other
// algorithms cannot be agreed upon". The other algorithms have
// already been checked above so the kex algorithm and host key
// algorithm are checked here.
if otherInit.FirstKexFollows && (clientInit.KexAlgos[0] != serverInit.KexAlgos[0] || clientInit.ServerHostKeyAlgos[0] != serverInit.ServerHostKeyAlgos[0]) {
// other side sent a kex message for the wrong algorithm,
// which we have to ignore.
if _, err := t.conn.readPacket(); err != nil {
return err
}
}
kex, ok := kexAlgoMap[t.algorithms.kex]
if !ok {
return fmt.Errorf("ssh: unexpected key exchange algorithm %v", t.algorithms.kex)
}
var result *kexResult
if len(t.hostKeys) > 0 {
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result, err = t.server(kex, &magics)
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} else {
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result, err = t.client(kex, &magics)
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}
if err != nil {
return err
}
firstKeyExchange := t.sessionID == nil
if firstKeyExchange {
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t.sessionID = result.H
}
result.SessionID = t.sessionID
if err := t.conn.prepareKeyChange(t.algorithms, result); err != nil {
return err
}
if err = t.conn.writePacket([]byte{msgNewKeys}); err != nil {
return err
}
// On the server side, after the first SSH_MSG_NEWKEYS, send a SSH_MSG_EXT_INFO
// message with the server-sig-algs extension if the client supports it. See
// RFC 8308, Sections 2.4 and 3.1, and [PROTOCOL], Section 1.9.
if !isClient && firstKeyExchange && contains(clientInit.KexAlgos, "ext-info-c") {
supportedPubKeyAuthAlgosList := strings.Join(t.publicKeyAuthAlgorithms, ",")
extInfo := &extInfoMsg{
NumExtensions: 2,
Payload: make([]byte, 0, 4+15+4+len(supportedPubKeyAuthAlgosList)+4+16+4+1),
}
extInfo.Payload = appendInt(extInfo.Payload, len("server-sig-algs"))
extInfo.Payload = append(extInfo.Payload, "server-sig-algs"...)
extInfo.Payload = appendInt(extInfo.Payload, len(supportedPubKeyAuthAlgosList))
extInfo.Payload = append(extInfo.Payload, supportedPubKeyAuthAlgosList...)
extInfo.Payload = appendInt(extInfo.Payload, len("ping@openssh.com"))
extInfo.Payload = append(extInfo.Payload, "ping@openssh.com"...)
extInfo.Payload = appendInt(extInfo.Payload, 1)
extInfo.Payload = append(extInfo.Payload, "0"...)
if err := t.conn.writePacket(Marshal(extInfo)); err != nil {
return err
}
}
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if packet, err := t.conn.readPacket(); err != nil {
return err
} else if packet[0] != msgNewKeys {
return unexpectedMessageError(msgNewKeys, packet[0])
}
if firstKeyExchange {
// Indicates to the transport that the first key exchange is completed
// after receiving SSH_MSG_NEWKEYS.
t.conn.setInitialKEXDone()
}
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return nil
}
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// algorithmSignerWrapper is an AlgorithmSigner that only supports the default
// key format algorithm.
//
// This is technically a violation of the AlgorithmSigner interface, but it
// should be unreachable given where we use this. Anyway, at least it returns an
// error instead of panicing or producing an incorrect signature.
type algorithmSignerWrapper struct {
Signer
}
func (a algorithmSignerWrapper) SignWithAlgorithm(rand io.Reader, data []byte, algorithm string) (*Signature, error) {
if algorithm != underlyingAlgo(a.PublicKey().Type()) {
return nil, errors.New("ssh: internal error: algorithmSignerWrapper invoked with non-default algorithm")
}
return a.Sign(rand, data)
}
func pickHostKey(hostKeys []Signer, algo string) AlgorithmSigner {
for _, k := range hostKeys {
if s, ok := k.(MultiAlgorithmSigner); ok {
if !contains(s.Algorithms(), underlyingAlgo(algo)) {
continue
}
}
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if algo == k.PublicKey().Type() {
return algorithmSignerWrapper{k}
}
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k, ok := k.(AlgorithmSigner)
if !ok {
continue
}
for _, a := range algorithmsForKeyFormat(k.PublicKey().Type()) {
if algo == a {
return k
}
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}
}
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return nil
}
func (t *handshakeTransport) server(kex kexAlgorithm, magics *handshakeMagics) (*kexResult, error) {
hostKey := pickHostKey(t.hostKeys, t.algorithms.hostKey)
if hostKey == nil {
return nil, errors.New("ssh: internal error: negotiated unsupported signature type")
}
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r, err := kex.Server(t.conn, t.config.Rand, magics, hostKey, t.algorithms.hostKey)
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return r, err
}
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func (t *handshakeTransport) client(kex kexAlgorithm, magics *handshakeMagics) (*kexResult, error) {
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result, err := kex.Client(t.conn, t.config.Rand, magics)
if err != nil {
return nil, err
}
hostKey, err := ParsePublicKey(result.HostKey)
if err != nil {
return nil, err
}
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if err := verifyHostKeySignature(hostKey, t.algorithms.hostKey, result); err != nil {
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return nil, err
}
err = t.hostKeyCallback(t.dialAddress, t.remoteAddr, hostKey)
if err != nil {
return nil, err
}
return result, nil
}