+++ /dev/null
-// 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"
- "errors"
- "io"
- "math/big"
-
- "golang.org/x/crypto/curve25519"
-)
-
-const (
- kexAlgoDH1SHA1 = "diffie-hellman-group1-sha1"
- kexAlgoDH14SHA1 = "diffie-hellman-group14-sha1"
- kexAlgoECDH256 = "ecdh-sha2-nistp256"
- kexAlgoECDH384 = "ecdh-sha2-nistp384"
- kexAlgoECDH521 = "ecdh-sha2-nistp521"
- kexAlgoCurve25519SHA256 = "curve25519-sha256@libssh.org"
-)
-
-// 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
- // with a hostkey.
- Server(p packetConn, rand io.Reader, magics *handshakeMagics, s Signer) (*kexResult, error)
-
- // 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
-}
-
-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) {
- hashFunc := crypto.SHA1
-
- 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
- }
-
- kInt, err := group.diffieHellman(kexDHReply.Y, x)
- if err != nil {
- return nil, err
- }
-
- h := hashFunc.New()
- magics.write(h)
- writeString(h, kexDHReply.HostKey)
- writeInt(h, X)
- writeInt(h, kexDHReply.Y)
- K := make([]byte, intLength(kInt))
- marshalInt(K, kInt)
- h.Write(K)
-
- return &kexResult{
- H: h.Sum(nil),
- K: K,
- HostKey: kexDHReply.HostKey,
- Signature: kexDHReply.Signature,
- Hash: crypto.SHA1,
- }, nil
-}
-
-func (group *dhGroup) Server(c packetConn, randSource io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) {
- hashFunc := crypto.SHA1
- 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)
- kInt, err := group.diffieHellman(kexDHInit.X, y)
- if err != nil {
- return nil, err
- }
-
- hostKeyBytes := priv.PublicKey().Marshal()
-
- h := hashFunc.New()
- magics.write(h)
- writeString(h, hostKeyBytes)
- writeInt(h, kexDHInit.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.
- sig, err := signAndMarshal(priv, randSource, H)
- 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,
- Hash: crypto.SHA1,
- }, nil
-}
-
-// 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
-}
-
-func (kex *ecdh) Server(c packetConn, rand io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) {
- 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.
- sig, err := signAndMarshal(priv, rand, H)
- 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
-}
-
-var kexAlgoMap = map[string]kexAlgorithm{}
-
-func init() {
- // This is the group called diffie-hellman-group1-sha1 in RFC
- // 4253 and Oakley Group 2 in RFC 2409.
- p, _ := new(big.Int).SetString("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF", 16)
- kexAlgoMap[kexAlgoDH1SHA1] = &dhGroup{
- g: new(big.Int).SetInt64(2),
- p: p,
- pMinus1: new(big.Int).Sub(p, bigOne),
- }
-
- // 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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
-
- kexAlgoMap[kexAlgoDH14SHA1] = &dhGroup{
- g: new(big.Int).SetInt64(2),
- p: p,
- pMinus1: new(big.Int).Sub(p, bigOne),
- }
-
- kexAlgoMap[kexAlgoECDH521] = &ecdh{elliptic.P521()}
- kexAlgoMap[kexAlgoECDH384] = &ecdh{elliptic.P384()}
- kexAlgoMap[kexAlgoECDH256] = &ecdh{elliptic.P256()}
- kexAlgoMap[kexAlgoCurve25519SHA256] = &curve25519sha256{}
-}
-
-// curve25519sha256 implements the curve25519-sha256@libssh.org key
-// agreement protocol, as described in
-// https://git.libssh.org/projects/libssh.git/tree/doc/curve25519-sha256@libssh.org.txt
-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)
-
- kInt := new(big.Int).SetBytes(secret[:])
- K := make([]byte, intLength(kInt))
- marshalInt(K, kInt)
- h.Write(K)
-
- return &kexResult{
- H: h.Sum(nil),
- K: K,
- HostKey: reply.HostKey,
- Signature: reply.Signature,
- Hash: crypto.SHA256,
- }, nil
-}
-
-func (kex *curve25519sha256) Server(c packetConn, rand io.Reader, magics *handshakeMagics, priv Signer) (result *kexResult, err error) {
- 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[:])
-
- kInt := new(big.Int).SetBytes(secret[:])
- K := make([]byte, intLength(kInt))
- marshalInt(K, kInt)
- h.Write(K)
-
- H := h.Sum(nil)
-
- sig, err := signAndMarshal(priv, rand, H)
- 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
-}
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