cloudflared-mirror/vendor/golang.org/x/crypto/ssh/kex.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"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/subtle"
"encoding/binary"
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"errors"
"fmt"
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"io"
"math/big"
"golang.org/x/crypto/curve25519"
)
const (
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kexAlgoDH1SHA1 = "diffie-hellman-group1-sha1"
kexAlgoDH14SHA1 = "diffie-hellman-group14-sha1"
kexAlgoDH14SHA256 = "diffie-hellman-group14-sha256"
kexAlgoECDH256 = "ecdh-sha2-nistp256"
kexAlgoECDH384 = "ecdh-sha2-nistp384"
kexAlgoECDH521 = "ecdh-sha2-nistp521"
kexAlgoCurve25519SHA256LibSSH = "curve25519-sha256@libssh.org"
kexAlgoCurve25519SHA256 = "curve25519-sha256"
// For the following kex only the client half contains a production
// ready implementation. The server half only consists of a minimal
// implementation to satisfy the automated tests.
kexAlgoDHGEXSHA1 = "diffie-hellman-group-exchange-sha1"
kexAlgoDHGEXSHA256 = "diffie-hellman-group-exchange-sha256"
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)
// kexResult captures the outcome of a key exchange.
type kexResult struct {
// Session hash. See also RFC 4253, section 8.
H []byte
// Shared secret. See also RFC 4253, section 8.
K []byte
// Host key as hashed into H.
HostKey []byte
// Signature of H.
Signature []byte
// A cryptographic hash function that matches the security
// level of the key exchange algorithm. It is used for
// calculating H, and for deriving keys from H and K.
Hash crypto.Hash
// The session ID, which is the first H computed. This is used
// to derive key material inside the transport.
SessionID []byte
}
// handshakeMagics contains data that is always included in the
// session hash.
type handshakeMagics struct {
clientVersion, serverVersion []byte
clientKexInit, serverKexInit []byte
}
func (m *handshakeMagics) write(w io.Writer) {
writeString(w, m.clientVersion)
writeString(w, m.serverVersion)
writeString(w, m.clientKexInit)
writeString(w, m.serverKexInit)
}
// kexAlgorithm abstracts different key exchange algorithms.
type kexAlgorithm interface {
// Server runs server-side key agreement, signing the result
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// with a hostkey. algo is the negotiated algorithm, and may
// be a certificate type.
Server(p packetConn, rand io.Reader, magics *handshakeMagics, s AlgorithmSigner, algo string) (*kexResult, error)
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// Client runs the client-side key agreement. Caller is
// responsible for verifying the host key signature.
Client(p packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error)
}
// dhGroup is a multiplicative group suitable for implementing Diffie-Hellman key agreement.
type dhGroup struct {
g, p, pMinus1 *big.Int
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hashFunc crypto.Hash
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}
func (group *dhGroup) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, error) {
if theirPublic.Cmp(bigOne) <= 0 || theirPublic.Cmp(group.pMinus1) >= 0 {
return nil, errors.New("ssh: DH parameter out of bounds")
}
return new(big.Int).Exp(theirPublic, myPrivate, group.p), nil
}
func (group *dhGroup) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) {
var x *big.Int
for {
var err error
if x, err = rand.Int(randSource, group.pMinus1); err != nil {
return nil, err
}
if x.Sign() > 0 {
break
}
}
X := new(big.Int).Exp(group.g, x, group.p)
kexDHInit := kexDHInitMsg{
X: X,
}
if err := c.writePacket(Marshal(&kexDHInit)); err != nil {
return nil, err
}
packet, err := c.readPacket()
if err != nil {
return nil, err
}
var kexDHReply kexDHReplyMsg
if err = Unmarshal(packet, &kexDHReply); err != nil {
return nil, err
}
ki, err := group.diffieHellman(kexDHReply.Y, x)
if err != nil {
return nil, err
}
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h := group.hashFunc.New()
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magics.write(h)
writeString(h, kexDHReply.HostKey)
writeInt(h, X)
writeInt(h, kexDHReply.Y)
K := make([]byte, intLength(ki))
marshalInt(K, ki)
h.Write(K)
return &kexResult{
H: h.Sum(nil),
K: K,
HostKey: kexDHReply.HostKey,
Signature: kexDHReply.Signature,
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Hash: group.hashFunc,
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}, nil
}
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func (group *dhGroup) Server(c packetConn, randSource io.Reader, magics *handshakeMagics, priv AlgorithmSigner, algo string) (result *kexResult, err error) {
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packet, err := c.readPacket()
if err != nil {
return
}
var kexDHInit kexDHInitMsg
if err = Unmarshal(packet, &kexDHInit); err != nil {
return
}
var y *big.Int
for {
if y, err = rand.Int(randSource, group.pMinus1); err != nil {
return
}
if y.Sign() > 0 {
break
}
}
Y := new(big.Int).Exp(group.g, y, group.p)
ki, err := group.diffieHellman(kexDHInit.X, y)
if err != nil {
return nil, err
}
hostKeyBytes := priv.PublicKey().Marshal()
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h := group.hashFunc.New()
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magics.write(h)
writeString(h, hostKeyBytes)
writeInt(h, kexDHInit.X)
writeInt(h, Y)
K := make([]byte, intLength(ki))
marshalInt(K, ki)
h.Write(K)
H := h.Sum(nil)
// H is already a hash, but the hostkey signing will apply its
// own key-specific hash algorithm.
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sig, err := signAndMarshal(priv, randSource, H, algo)
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if err != nil {
return nil, err
}
kexDHReply := kexDHReplyMsg{
HostKey: hostKeyBytes,
Y: Y,
Signature: sig,
}
packet = Marshal(&kexDHReply)
err = c.writePacket(packet)
return &kexResult{
H: H,
K: K,
HostKey: hostKeyBytes,
Signature: sig,
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Hash: group.hashFunc,
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}, err
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}
// ecdh performs Elliptic Curve Diffie-Hellman key exchange as
// described in RFC 5656, section 4.
type ecdh struct {
curve elliptic.Curve
}
func (kex *ecdh) Client(c packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error) {
ephKey, err := ecdsa.GenerateKey(kex.curve, rand)
if err != nil {
return nil, err
}
kexInit := kexECDHInitMsg{
ClientPubKey: elliptic.Marshal(kex.curve, ephKey.PublicKey.X, ephKey.PublicKey.Y),
}
serialized := Marshal(&kexInit)
if err := c.writePacket(serialized); err != nil {
return nil, err
}
packet, err := c.readPacket()
if err != nil {
return nil, err
}
var reply kexECDHReplyMsg
if err = Unmarshal(packet, &reply); err != nil {
return nil, err
}
x, y, err := unmarshalECKey(kex.curve, reply.EphemeralPubKey)
if err != nil {
return nil, err
}
// generate shared secret
secret, _ := kex.curve.ScalarMult(x, y, ephKey.D.Bytes())
h := ecHash(kex.curve).New()
magics.write(h)
writeString(h, reply.HostKey)
writeString(h, kexInit.ClientPubKey)
writeString(h, reply.EphemeralPubKey)
K := make([]byte, intLength(secret))
marshalInt(K, secret)
h.Write(K)
return &kexResult{
H: h.Sum(nil),
K: K,
HostKey: reply.HostKey,
Signature: reply.Signature,
Hash: ecHash(kex.curve),
}, nil
}
// unmarshalECKey parses and checks an EC key.
func unmarshalECKey(curve elliptic.Curve, pubkey []byte) (x, y *big.Int, err error) {
x, y = elliptic.Unmarshal(curve, pubkey)
if x == nil {
return nil, nil, errors.New("ssh: elliptic.Unmarshal failure")
}
if !validateECPublicKey(curve, x, y) {
return nil, nil, errors.New("ssh: public key not on curve")
}
return x, y, nil
}
// validateECPublicKey checks that the point is a valid public key for
// the given curve. See [SEC1], 3.2.2
func validateECPublicKey(curve elliptic.Curve, x, y *big.Int) bool {
if x.Sign() == 0 && y.Sign() == 0 {
return false
}
if x.Cmp(curve.Params().P) >= 0 {
return false
}
if y.Cmp(curve.Params().P) >= 0 {
return false
}
if !curve.IsOnCurve(x, y) {
return false
}
// We don't check if N * PubKey == 0, since
//
// - the NIST curves have cofactor = 1, so this is implicit.
// (We don't foresee an implementation that supports non NIST
// curves)
//
// - for ephemeral keys, we don't need to worry about small
// subgroup attacks.
return true
}
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func (kex *ecdh) Server(c packetConn, rand io.Reader, magics *handshakeMagics, priv AlgorithmSigner, algo string) (result *kexResult, err error) {
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packet, err := c.readPacket()
if err != nil {
return nil, err
}
var kexECDHInit kexECDHInitMsg
if err = Unmarshal(packet, &kexECDHInit); err != nil {
return nil, err
}
clientX, clientY, err := unmarshalECKey(kex.curve, kexECDHInit.ClientPubKey)
if err != nil {
return nil, err
}
// We could cache this key across multiple users/multiple
// connection attempts, but the benefit is small. OpenSSH
// generates a new key for each incoming connection.
ephKey, err := ecdsa.GenerateKey(kex.curve, rand)
if err != nil {
return nil, err
}
hostKeyBytes := priv.PublicKey().Marshal()
serializedEphKey := elliptic.Marshal(kex.curve, ephKey.PublicKey.X, ephKey.PublicKey.Y)
// generate shared secret
secret, _ := kex.curve.ScalarMult(clientX, clientY, ephKey.D.Bytes())
h := ecHash(kex.curve).New()
magics.write(h)
writeString(h, hostKeyBytes)
writeString(h, kexECDHInit.ClientPubKey)
writeString(h, serializedEphKey)
K := make([]byte, intLength(secret))
marshalInt(K, secret)
h.Write(K)
H := h.Sum(nil)
// H is already a hash, but the hostkey signing will apply its
// own key-specific hash algorithm.
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sig, err := signAndMarshal(priv, rand, H, algo)
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if err != nil {
return nil, err
}
reply := kexECDHReplyMsg{
EphemeralPubKey: serializedEphKey,
HostKey: hostKeyBytes,
Signature: sig,
}
serialized := Marshal(&reply)
if err := c.writePacket(serialized); err != nil {
return nil, err
}
return &kexResult{
H: H,
K: K,
HostKey: reply.HostKey,
Signature: sig,
Hash: ecHash(kex.curve),
}, nil
}
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// ecHash returns the hash to match the given elliptic curve, see RFC
// 5656, section 6.2.1
func ecHash(curve elliptic.Curve) crypto.Hash {
bitSize := curve.Params().BitSize
switch {
case bitSize <= 256:
return crypto.SHA256
case bitSize <= 384:
return crypto.SHA384
}
return crypto.SHA512
}
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var kexAlgoMap = map[string]kexAlgorithm{}
func init() {
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// This is the group called diffie-hellman-group1-sha1 in
// RFC 4253 and Oakley Group 2 in RFC 2409.
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p, _ := new(big.Int).SetString("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF", 16)
kexAlgoMap[kexAlgoDH1SHA1] = &dhGroup{
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g: new(big.Int).SetInt64(2),
p: p,
pMinus1: new(big.Int).Sub(p, bigOne),
hashFunc: crypto.SHA1,
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}
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// This are the groups called diffie-hellman-group14-sha1 and
// diffie-hellman-group14-sha256 in RFC 4253 and RFC 8268,
// and Oakley Group 14 in RFC 3526.
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p, _ = new(big.Int).SetString("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE45B3DC2007CB8A163BF0598DA48361C55D39A69163FA8FD24CF5F83655D23DCA3AD961C62F356208552BB9ED529077096966D670C354E4ABC9804F1746C08CA18217C32905E462E36CE3BE39E772C180E86039B2783A2EC07A28FB5C55DF06F4C52C9DE2BCBF6955817183995497CEA956AE515D2261898FA051015728E5A8AACAA68FFFFFFFFFFFFFFFF", 16)
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group14 := &dhGroup{
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g: new(big.Int).SetInt64(2),
p: p,
pMinus1: new(big.Int).Sub(p, bigOne),
}
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kexAlgoMap[kexAlgoDH14SHA1] = &dhGroup{
g: group14.g, p: group14.p, pMinus1: group14.pMinus1,
hashFunc: crypto.SHA1,
}
kexAlgoMap[kexAlgoDH14SHA256] = &dhGroup{
g: group14.g, p: group14.p, pMinus1: group14.pMinus1,
hashFunc: crypto.SHA256,
}
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kexAlgoMap[kexAlgoECDH521] = &ecdh{elliptic.P521()}
kexAlgoMap[kexAlgoECDH384] = &ecdh{elliptic.P384()}
kexAlgoMap[kexAlgoECDH256] = &ecdh{elliptic.P256()}
kexAlgoMap[kexAlgoCurve25519SHA256] = &curve25519sha256{}
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kexAlgoMap[kexAlgoCurve25519SHA256LibSSH] = &curve25519sha256{}
kexAlgoMap[kexAlgoDHGEXSHA1] = &dhGEXSHA{hashFunc: crypto.SHA1}
kexAlgoMap[kexAlgoDHGEXSHA256] = &dhGEXSHA{hashFunc: crypto.SHA256}
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}
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// curve25519sha256 implements the curve25519-sha256 (formerly known as
// curve25519-sha256@libssh.org) key exchange method, as described in RFC 8731.
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type curve25519sha256 struct{}
type curve25519KeyPair struct {
priv [32]byte
pub [32]byte
}
func (kp *curve25519KeyPair) generate(rand io.Reader) error {
if _, err := io.ReadFull(rand, kp.priv[:]); err != nil {
return err
}
curve25519.ScalarBaseMult(&kp.pub, &kp.priv)
return nil
}
// curve25519Zeros is just an array of 32 zero bytes so that we have something
// convenient to compare against in order to reject curve25519 points with the
// wrong order.
var curve25519Zeros [32]byte
func (kex *curve25519sha256) Client(c packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error) {
var kp curve25519KeyPair
if err := kp.generate(rand); err != nil {
return nil, err
}
if err := c.writePacket(Marshal(&kexECDHInitMsg{kp.pub[:]})); err != nil {
return nil, err
}
packet, err := c.readPacket()
if err != nil {
return nil, err
}
var reply kexECDHReplyMsg
if err = Unmarshal(packet, &reply); err != nil {
return nil, err
}
if len(reply.EphemeralPubKey) != 32 {
return nil, errors.New("ssh: peer's curve25519 public value has wrong length")
}
var servPub, secret [32]byte
copy(servPub[:], reply.EphemeralPubKey)
curve25519.ScalarMult(&secret, &kp.priv, &servPub)
if subtle.ConstantTimeCompare(secret[:], curve25519Zeros[:]) == 1 {
return nil, errors.New("ssh: peer's curve25519 public value has wrong order")
}
h := crypto.SHA256.New()
magics.write(h)
writeString(h, reply.HostKey)
writeString(h, kp.pub[:])
writeString(h, reply.EphemeralPubKey)
ki := new(big.Int).SetBytes(secret[:])
K := make([]byte, intLength(ki))
marshalInt(K, ki)
h.Write(K)
return &kexResult{
H: h.Sum(nil),
K: K,
HostKey: reply.HostKey,
Signature: reply.Signature,
Hash: crypto.SHA256,
}, nil
}
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func (kex *curve25519sha256) Server(c packetConn, rand io.Reader, magics *handshakeMagics, priv AlgorithmSigner, algo string) (result *kexResult, err error) {
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packet, err := c.readPacket()
if err != nil {
return
}
var kexInit kexECDHInitMsg
if err = Unmarshal(packet, &kexInit); err != nil {
return
}
if len(kexInit.ClientPubKey) != 32 {
return nil, errors.New("ssh: peer's curve25519 public value has wrong length")
}
var kp curve25519KeyPair
if err := kp.generate(rand); err != nil {
return nil, err
}
var clientPub, secret [32]byte
copy(clientPub[:], kexInit.ClientPubKey)
curve25519.ScalarMult(&secret, &kp.priv, &clientPub)
if subtle.ConstantTimeCompare(secret[:], curve25519Zeros[:]) == 1 {
return nil, errors.New("ssh: peer's curve25519 public value has wrong order")
}
hostKeyBytes := priv.PublicKey().Marshal()
h := crypto.SHA256.New()
magics.write(h)
writeString(h, hostKeyBytes)
writeString(h, kexInit.ClientPubKey)
writeString(h, kp.pub[:])
ki := new(big.Int).SetBytes(secret[:])
K := make([]byte, intLength(ki))
marshalInt(K, ki)
h.Write(K)
H := h.Sum(nil)
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sig, err := signAndMarshal(priv, rand, H, algo)
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if err != nil {
return nil, err
}
reply := kexECDHReplyMsg{
EphemeralPubKey: kp.pub[:],
HostKey: hostKeyBytes,
Signature: sig,
}
if err := c.writePacket(Marshal(&reply)); err != nil {
return nil, err
}
return &kexResult{
H: H,
K: K,
HostKey: hostKeyBytes,
Signature: sig,
Hash: crypto.SHA256,
}, nil
}
// dhGEXSHA implements the diffie-hellman-group-exchange-sha1 and
// diffie-hellman-group-exchange-sha256 key agreement protocols,
// as described in RFC 4419
type dhGEXSHA struct {
hashFunc crypto.Hash
}
const (
dhGroupExchangeMinimumBits = 2048
dhGroupExchangePreferredBits = 2048
dhGroupExchangeMaximumBits = 8192
)
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func (gex *dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) {
// Send GexRequest
kexDHGexRequest := kexDHGexRequestMsg{
MinBits: dhGroupExchangeMinimumBits,
PreferedBits: dhGroupExchangePreferredBits,
MaxBits: dhGroupExchangeMaximumBits,
}
if err := c.writePacket(Marshal(&kexDHGexRequest)); err != nil {
return nil, err
}
// Receive GexGroup
packet, err := c.readPacket()
if err != nil {
return nil, err
}
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var msg kexDHGexGroupMsg
if err = Unmarshal(packet, &msg); err != nil {
return nil, err
}
// reject if p's bit length < dhGroupExchangeMinimumBits or > dhGroupExchangeMaximumBits
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if msg.P.BitLen() < dhGroupExchangeMinimumBits || msg.P.BitLen() > dhGroupExchangeMaximumBits {
return nil, fmt.Errorf("ssh: server-generated gex p is out of range (%d bits)", msg.P.BitLen())
}
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// Check if g is safe by verifying that 1 < g < p-1
pMinusOne := new(big.Int).Sub(msg.P, bigOne)
if msg.G.Cmp(bigOne) <= 0 || msg.G.Cmp(pMinusOne) >= 0 {
return nil, fmt.Errorf("ssh: server provided gex g is not safe")
}
// Send GexInit
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pHalf := new(big.Int).Rsh(msg.P, 1)
x, err := rand.Int(randSource, pHalf)
if err != nil {
return nil, err
}
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X := new(big.Int).Exp(msg.G, x, msg.P)
kexDHGexInit := kexDHGexInitMsg{
X: X,
}
if err := c.writePacket(Marshal(&kexDHGexInit)); err != nil {
return nil, err
}
// Receive GexReply
packet, err = c.readPacket()
if err != nil {
return nil, err
}
var kexDHGexReply kexDHGexReplyMsg
if err = Unmarshal(packet, &kexDHGexReply); err != nil {
return nil, err
}
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if kexDHGexReply.Y.Cmp(bigOne) <= 0 || kexDHGexReply.Y.Cmp(pMinusOne) >= 0 {
return nil, errors.New("ssh: DH parameter out of bounds")
}
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kInt := new(big.Int).Exp(kexDHGexReply.Y, x, msg.P)
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// Check if k is safe by verifying that k > 1 and k < p - 1
if kInt.Cmp(bigOne) <= 0 || kInt.Cmp(pMinusOne) >= 0 {
return nil, fmt.Errorf("ssh: derived k is not safe")
}
h := gex.hashFunc.New()
magics.write(h)
writeString(h, kexDHGexReply.HostKey)
binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits))
binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits))
binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits))
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writeInt(h, msg.P)
writeInt(h, msg.G)
writeInt(h, X)
writeInt(h, kexDHGexReply.Y)
K := make([]byte, intLength(kInt))
marshalInt(K, kInt)
h.Write(K)
return &kexResult{
H: h.Sum(nil),
K: K,
HostKey: kexDHGexReply.HostKey,
Signature: kexDHGexReply.Signature,
Hash: gex.hashFunc,
}, nil
}
// Server half implementation of the Diffie Hellman Key Exchange with SHA1 and SHA256.
//
// This is a minimal implementation to satisfy the automated tests.
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func (gex dhGEXSHA) Server(c packetConn, randSource io.Reader, magics *handshakeMagics, priv AlgorithmSigner, algo string) (result *kexResult, err error) {
// Receive GexRequest
packet, err := c.readPacket()
if err != nil {
return
}
var kexDHGexRequest kexDHGexRequestMsg
if err = Unmarshal(packet, &kexDHGexRequest); err != nil {
return
}
// Send GexGroup
// This is the group called diffie-hellman-group14-sha1 in RFC
// 4253 and Oakley Group 14 in RFC 3526.
p, _ := new(big.Int).SetString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g := big.NewInt(2)
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msg := &kexDHGexGroupMsg{
P: p,
G: g,
}
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if err := c.writePacket(Marshal(msg)); err != nil {
return nil, err
}
// Receive GexInit
packet, err = c.readPacket()
if err != nil {
return
}
var kexDHGexInit kexDHGexInitMsg
if err = Unmarshal(packet, &kexDHGexInit); err != nil {
return
}
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pHalf := new(big.Int).Rsh(p, 1)
y, err := rand.Int(randSource, pHalf)
if err != nil {
return
}
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Y := new(big.Int).Exp(g, y, p)
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pMinusOne := new(big.Int).Sub(p, bigOne)
if kexDHGexInit.X.Cmp(bigOne) <= 0 || kexDHGexInit.X.Cmp(pMinusOne) >= 0 {
return nil, errors.New("ssh: DH parameter out of bounds")
}
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kInt := new(big.Int).Exp(kexDHGexInit.X, y, p)
hostKeyBytes := priv.PublicKey().Marshal()
h := gex.hashFunc.New()
magics.write(h)
writeString(h, hostKeyBytes)
binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits))
binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits))
binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits))
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writeInt(h, p)
writeInt(h, g)
writeInt(h, kexDHGexInit.X)
writeInt(h, Y)
K := make([]byte, intLength(kInt))
marshalInt(K, kInt)
h.Write(K)
H := h.Sum(nil)
// H is already a hash, but the hostkey signing will apply its
// own key-specific hash algorithm.
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sig, err := signAndMarshal(priv, randSource, H, algo)
if err != nil {
return nil, err
}
kexDHGexReply := kexDHGexReplyMsg{
HostKey: hostKeyBytes,
Y: Y,
Signature: sig,
}
packet = Marshal(&kexDHGexReply)
err = c.writePacket(packet)
return &kexResult{
H: H,
K: K,
HostKey: hostKeyBytes,
Signature: sig,
Hash: gex.hashFunc,
}, err
}