mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2025-10-31 17:52:25 -05:00
786 lines
22 KiB
Go
786 lines
22 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package ssh
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import (
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"crypto"
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"crypto/ecdsa"
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"crypto/elliptic"
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"crypto/rand"
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"crypto/subtle"
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"math/big"
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"golang.org/x/crypto/curve25519"
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)
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const (
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kexAlgoDH1SHA1 = "diffie-hellman-group1-sha1"
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kexAlgoDH14SHA1 = "diffie-hellman-group14-sha1"
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kexAlgoDH14SHA256 = "diffie-hellman-group14-sha256"
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kexAlgoDH16SHA512 = "diffie-hellman-group16-sha512"
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kexAlgoECDH256 = "ecdh-sha2-nistp256"
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kexAlgoECDH384 = "ecdh-sha2-nistp384"
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kexAlgoECDH521 = "ecdh-sha2-nistp521"
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kexAlgoCurve25519SHA256LibSSH = "curve25519-sha256@libssh.org"
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kexAlgoCurve25519SHA256 = "curve25519-sha256"
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// For the following kex only the client half contains a production
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// ready implementation. The server half only consists of a minimal
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// implementation to satisfy the automated tests.
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kexAlgoDHGEXSHA1 = "diffie-hellman-group-exchange-sha1"
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kexAlgoDHGEXSHA256 = "diffie-hellman-group-exchange-sha256"
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)
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// kexResult captures the outcome of a key exchange.
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type kexResult struct {
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// Session hash. See also RFC 4253, section 8.
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H []byte
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// Shared secret. See also RFC 4253, section 8.
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K []byte
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// Host key as hashed into H.
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HostKey []byte
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// Signature of H.
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Signature []byte
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// A cryptographic hash function that matches the security
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// level of the key exchange algorithm. It is used for
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// calculating H, and for deriving keys from H and K.
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Hash crypto.Hash
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// The session ID, which is the first H computed. This is used
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// to derive key material inside the transport.
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SessionID []byte
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}
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// handshakeMagics contains data that is always included in the
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// session hash.
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type handshakeMagics struct {
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clientVersion, serverVersion []byte
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clientKexInit, serverKexInit []byte
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}
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func (m *handshakeMagics) write(w io.Writer) {
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writeString(w, m.clientVersion)
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writeString(w, m.serverVersion)
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writeString(w, m.clientKexInit)
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writeString(w, m.serverKexInit)
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}
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// kexAlgorithm abstracts different key exchange algorithms.
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type kexAlgorithm interface {
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// Server runs server-side key agreement, signing the result
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// with a hostkey. algo is the negotiated algorithm, and may
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// be a certificate type.
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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
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// responsible for verifying the host key signature.
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Client(p packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error)
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}
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// dhGroup is a multiplicative group suitable for implementing Diffie-Hellman key agreement.
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type dhGroup struct {
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g, p, pMinus1 *big.Int
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hashFunc crypto.Hash
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}
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func (group *dhGroup) diffieHellman(theirPublic, myPrivate *big.Int) (*big.Int, error) {
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if theirPublic.Cmp(bigOne) <= 0 || theirPublic.Cmp(group.pMinus1) >= 0 {
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return nil, errors.New("ssh: DH parameter out of bounds")
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}
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return new(big.Int).Exp(theirPublic, myPrivate, group.p), nil
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}
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func (group *dhGroup) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) {
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var x *big.Int
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for {
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var err error
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if x, err = rand.Int(randSource, group.pMinus1); err != nil {
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return nil, err
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}
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if x.Sign() > 0 {
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break
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}
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}
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X := new(big.Int).Exp(group.g, x, group.p)
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kexDHInit := kexDHInitMsg{
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X: X,
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}
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if err := c.writePacket(Marshal(&kexDHInit)); err != nil {
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return nil, err
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}
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packet, err := c.readPacket()
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if err != nil {
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return nil, err
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}
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var kexDHReply kexDHReplyMsg
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if err = Unmarshal(packet, &kexDHReply); err != nil {
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return nil, err
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}
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ki, err := group.diffieHellman(kexDHReply.Y, x)
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if err != nil {
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return nil, err
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}
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h := group.hashFunc.New()
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magics.write(h)
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writeString(h, kexDHReply.HostKey)
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writeInt(h, X)
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writeInt(h, kexDHReply.Y)
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K := make([]byte, intLength(ki))
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marshalInt(K, ki)
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h.Write(K)
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return &kexResult{
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H: h.Sum(nil),
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K: K,
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HostKey: kexDHReply.HostKey,
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Signature: kexDHReply.Signature,
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Hash: group.hashFunc,
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}, nil
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}
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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()
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if err != nil {
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return
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}
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var kexDHInit kexDHInitMsg
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if err = Unmarshal(packet, &kexDHInit); err != nil {
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return
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}
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var y *big.Int
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for {
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if y, err = rand.Int(randSource, group.pMinus1); err != nil {
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return
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}
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if y.Sign() > 0 {
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break
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}
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}
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Y := new(big.Int).Exp(group.g, y, group.p)
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ki, err := group.diffieHellman(kexDHInit.X, y)
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if err != nil {
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return nil, err
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}
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hostKeyBytes := priv.PublicKey().Marshal()
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h := group.hashFunc.New()
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magics.write(h)
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writeString(h, hostKeyBytes)
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writeInt(h, kexDHInit.X)
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writeInt(h, Y)
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K := make([]byte, intLength(ki))
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marshalInt(K, ki)
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h.Write(K)
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H := h.Sum(nil)
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// H is already a hash, but the hostkey signing will apply its
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// own key-specific hash algorithm.
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sig, err := signAndMarshal(priv, randSource, H, algo)
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if err != nil {
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return nil, err
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}
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kexDHReply := kexDHReplyMsg{
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HostKey: hostKeyBytes,
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Y: Y,
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Signature: sig,
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}
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packet = Marshal(&kexDHReply)
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err = c.writePacket(packet)
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return &kexResult{
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H: H,
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K: K,
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HostKey: hostKeyBytes,
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Signature: sig,
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Hash: group.hashFunc,
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}, err
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}
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// ecdh performs Elliptic Curve Diffie-Hellman key exchange as
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// described in RFC 5656, section 4.
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type ecdh struct {
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curve elliptic.Curve
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}
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func (kex *ecdh) Client(c packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error) {
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ephKey, err := ecdsa.GenerateKey(kex.curve, rand)
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if err != nil {
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return nil, err
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}
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kexInit := kexECDHInitMsg{
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ClientPubKey: elliptic.Marshal(kex.curve, ephKey.PublicKey.X, ephKey.PublicKey.Y),
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}
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serialized := Marshal(&kexInit)
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if err := c.writePacket(serialized); err != nil {
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return nil, err
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}
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packet, err := c.readPacket()
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if err != nil {
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return nil, err
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}
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var reply kexECDHReplyMsg
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if err = Unmarshal(packet, &reply); err != nil {
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return nil, err
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}
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x, y, err := unmarshalECKey(kex.curve, reply.EphemeralPubKey)
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if err != nil {
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return nil, err
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}
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// generate shared secret
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secret, _ := kex.curve.ScalarMult(x, y, ephKey.D.Bytes())
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h := ecHash(kex.curve).New()
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magics.write(h)
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writeString(h, reply.HostKey)
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writeString(h, kexInit.ClientPubKey)
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writeString(h, reply.EphemeralPubKey)
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K := make([]byte, intLength(secret))
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marshalInt(K, secret)
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h.Write(K)
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return &kexResult{
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H: h.Sum(nil),
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K: K,
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HostKey: reply.HostKey,
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Signature: reply.Signature,
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Hash: ecHash(kex.curve),
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}, nil
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}
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// unmarshalECKey parses and checks an EC key.
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func unmarshalECKey(curve elliptic.Curve, pubkey []byte) (x, y *big.Int, err error) {
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x, y = elliptic.Unmarshal(curve, pubkey)
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if x == nil {
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return nil, nil, errors.New("ssh: elliptic.Unmarshal failure")
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}
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if !validateECPublicKey(curve, x, y) {
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return nil, nil, errors.New("ssh: public key not on curve")
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}
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return x, y, nil
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}
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// validateECPublicKey checks that the point is a valid public key for
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// the given curve. See [SEC1], 3.2.2
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func validateECPublicKey(curve elliptic.Curve, x, y *big.Int) bool {
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if x.Sign() == 0 && y.Sign() == 0 {
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return false
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}
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if x.Cmp(curve.Params().P) >= 0 {
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return false
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}
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if y.Cmp(curve.Params().P) >= 0 {
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return false
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}
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if !curve.IsOnCurve(x, y) {
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return false
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}
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// We don't check if N * PubKey == 0, since
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//
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// - the NIST curves have cofactor = 1, so this is implicit.
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// (We don't foresee an implementation that supports non NIST
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// curves)
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//
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// - for ephemeral keys, we don't need to worry about small
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// subgroup attacks.
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return true
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}
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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()
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if err != nil {
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return nil, err
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}
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var kexECDHInit kexECDHInitMsg
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if err = Unmarshal(packet, &kexECDHInit); err != nil {
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return nil, err
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}
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clientX, clientY, err := unmarshalECKey(kex.curve, kexECDHInit.ClientPubKey)
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if err != nil {
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return nil, err
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}
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// We could cache this key across multiple users/multiple
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// connection attempts, but the benefit is small. OpenSSH
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// generates a new key for each incoming connection.
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ephKey, err := ecdsa.GenerateKey(kex.curve, rand)
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if err != nil {
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return nil, err
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}
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hostKeyBytes := priv.PublicKey().Marshal()
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serializedEphKey := elliptic.Marshal(kex.curve, ephKey.PublicKey.X, ephKey.PublicKey.Y)
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// generate shared secret
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secret, _ := kex.curve.ScalarMult(clientX, clientY, ephKey.D.Bytes())
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h := ecHash(kex.curve).New()
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magics.write(h)
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writeString(h, hostKeyBytes)
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writeString(h, kexECDHInit.ClientPubKey)
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writeString(h, serializedEphKey)
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K := make([]byte, intLength(secret))
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marshalInt(K, secret)
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h.Write(K)
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H := h.Sum(nil)
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// H is already a hash, but the hostkey signing will apply its
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// own key-specific hash algorithm.
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sig, err := signAndMarshal(priv, rand, H, algo)
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if err != nil {
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return nil, err
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}
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reply := kexECDHReplyMsg{
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EphemeralPubKey: serializedEphKey,
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HostKey: hostKeyBytes,
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Signature: sig,
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}
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serialized := Marshal(&reply)
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if err := c.writePacket(serialized); err != nil {
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return nil, err
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}
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return &kexResult{
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H: H,
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K: K,
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HostKey: reply.HostKey,
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Signature: sig,
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Hash: ecHash(kex.curve),
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}, nil
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}
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// ecHash returns the hash to match the given elliptic curve, see RFC
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// 5656, section 6.2.1
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func ecHash(curve elliptic.Curve) crypto.Hash {
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bitSize := curve.Params().BitSize
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switch {
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case bitSize <= 256:
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return crypto.SHA256
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case bitSize <= 384:
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return crypto.SHA384
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}
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return crypto.SHA512
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}
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var kexAlgoMap = map[string]kexAlgorithm{}
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func init() {
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// This is the group called diffie-hellman-group1-sha1 in
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// RFC 4253 and Oakley Group 2 in RFC 2409.
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p, _ := new(big.Int).SetString("FFFFFFFFFFFFFFFFC90FDAA22168C234C4C6628B80DC1CD129024E088A67CC74020BBEA63B139B22514A08798E3404DDEF9519B3CD3A431B302B0A6DF25F14374FE1356D6D51C245E485B576625E7EC6F44C42E9A637ED6B0BFF5CB6F406B7EDEE386BFB5A899FA5AE9F24117C4B1FE649286651ECE65381FFFFFFFFFFFFFFFF", 16)
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kexAlgoMap[kexAlgoDH1SHA1] = &dhGroup{
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g: new(big.Int).SetInt64(2),
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p: p,
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pMinus1: new(big.Int).Sub(p, bigOne),
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hashFunc: crypto.SHA1,
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}
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// This are the groups called diffie-hellman-group14-sha1 and
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// diffie-hellman-group14-sha256 in RFC 4253 and RFC 8268,
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// and Oakley Group 14 in RFC 3526.
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p, _ = new(big.Int).SetString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group14 := &dhGroup{
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g: new(big.Int).SetInt64(2),
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p: p,
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pMinus1: new(big.Int).Sub(p, bigOne),
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}
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kexAlgoMap[kexAlgoDH14SHA1] = &dhGroup{
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g: group14.g, p: group14.p, pMinus1: group14.pMinus1,
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hashFunc: crypto.SHA1,
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}
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kexAlgoMap[kexAlgoDH14SHA256] = &dhGroup{
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g: group14.g, p: group14.p, pMinus1: group14.pMinus1,
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hashFunc: crypto.SHA256,
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}
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// This is the group called diffie-hellman-group16-sha512 in RFC
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// 8268 and Oakley Group 16 in RFC 3526.
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p, _ = new(big.Int).SetString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kexAlgoMap[kexAlgoDH16SHA512] = &dhGroup{
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g: new(big.Int).SetInt64(2),
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p: p,
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pMinus1: new(big.Int).Sub(p, bigOne),
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hashFunc: crypto.SHA512,
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}
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kexAlgoMap[kexAlgoECDH521] = &ecdh{elliptic.P521()}
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kexAlgoMap[kexAlgoECDH384] = &ecdh{elliptic.P384()}
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kexAlgoMap[kexAlgoECDH256] = &ecdh{elliptic.P256()}
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kexAlgoMap[kexAlgoCurve25519SHA256] = &curve25519sha256{}
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kexAlgoMap[kexAlgoCurve25519SHA256LibSSH] = &curve25519sha256{}
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kexAlgoMap[kexAlgoDHGEXSHA1] = &dhGEXSHA{hashFunc: crypto.SHA1}
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kexAlgoMap[kexAlgoDHGEXSHA256] = &dhGEXSHA{hashFunc: crypto.SHA256}
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}
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// curve25519sha256 implements the curve25519-sha256 (formerly known as
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// curve25519-sha256@libssh.org) key exchange method, as described in RFC 8731.
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type curve25519sha256 struct{}
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type curve25519KeyPair struct {
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priv [32]byte
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pub [32]byte
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}
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func (kp *curve25519KeyPair) generate(rand io.Reader) error {
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if _, err := io.ReadFull(rand, kp.priv[:]); err != nil {
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return err
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}
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curve25519.ScalarBaseMult(&kp.pub, &kp.priv)
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return nil
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}
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// curve25519Zeros is just an array of 32 zero bytes so that we have something
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// convenient to compare against in order to reject curve25519 points with the
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// wrong order.
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var curve25519Zeros [32]byte
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func (kex *curve25519sha256) Client(c packetConn, rand io.Reader, magics *handshakeMagics) (*kexResult, error) {
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var kp curve25519KeyPair
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if err := kp.generate(rand); err != nil {
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return nil, err
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}
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if err := c.writePacket(Marshal(&kexECDHInitMsg{kp.pub[:]})); err != nil {
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return nil, err
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}
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packet, err := c.readPacket()
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if err != nil {
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return nil, err
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}
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var reply kexECDHReplyMsg
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if err = Unmarshal(packet, &reply); err != nil {
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return nil, err
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}
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if len(reply.EphemeralPubKey) != 32 {
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return nil, errors.New("ssh: peer's curve25519 public value has wrong length")
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}
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var servPub, secret [32]byte
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copy(servPub[:], reply.EphemeralPubKey)
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curve25519.ScalarMult(&secret, &kp.priv, &servPub)
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if subtle.ConstantTimeCompare(secret[:], curve25519Zeros[:]) == 1 {
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return nil, errors.New("ssh: peer's curve25519 public value has wrong order")
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}
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h := crypto.SHA256.New()
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magics.write(h)
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writeString(h, reply.HostKey)
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writeString(h, kp.pub[:])
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writeString(h, reply.EphemeralPubKey)
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ki := new(big.Int).SetBytes(secret[:])
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K := make([]byte, intLength(ki))
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marshalInt(K, ki)
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h.Write(K)
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return &kexResult{
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H: h.Sum(nil),
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K: K,
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HostKey: reply.HostKey,
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Signature: reply.Signature,
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Hash: crypto.SHA256,
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}, nil
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}
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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()
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if err != nil {
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return
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}
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var kexInit kexECDHInitMsg
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if err = Unmarshal(packet, &kexInit); err != nil {
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return
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}
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if len(kexInit.ClientPubKey) != 32 {
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return nil, errors.New("ssh: peer's curve25519 public value has wrong length")
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}
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var kp curve25519KeyPair
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if err := kp.generate(rand); err != nil {
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return nil, err
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}
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var clientPub, secret [32]byte
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copy(clientPub[:], kexInit.ClientPubKey)
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curve25519.ScalarMult(&secret, &kp.priv, &clientPub)
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if subtle.ConstantTimeCompare(secret[:], curve25519Zeros[:]) == 1 {
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return nil, errors.New("ssh: peer's curve25519 public value has wrong order")
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}
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hostKeyBytes := priv.PublicKey().Marshal()
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h := crypto.SHA256.New()
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magics.write(h)
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writeString(h, hostKeyBytes)
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writeString(h, kexInit.ClientPubKey)
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writeString(h, kp.pub[:])
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ki := new(big.Int).SetBytes(secret[:])
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K := make([]byte, intLength(ki))
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marshalInt(K, ki)
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h.Write(K)
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H := h.Sum(nil)
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sig, err := signAndMarshal(priv, rand, H, algo)
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if err != nil {
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return nil, err
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}
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reply := kexECDHReplyMsg{
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EphemeralPubKey: kp.pub[:],
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HostKey: hostKeyBytes,
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Signature: sig,
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}
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if err := c.writePacket(Marshal(&reply)); err != nil {
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return nil, err
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}
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return &kexResult{
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H: H,
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K: K,
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HostKey: hostKeyBytes,
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Signature: sig,
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Hash: crypto.SHA256,
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}, nil
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}
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// dhGEXSHA implements the diffie-hellman-group-exchange-sha1 and
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// diffie-hellman-group-exchange-sha256 key agreement protocols,
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// as described in RFC 4419
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type dhGEXSHA struct {
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hashFunc crypto.Hash
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}
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const (
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dhGroupExchangeMinimumBits = 2048
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dhGroupExchangePreferredBits = 2048
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dhGroupExchangeMaximumBits = 8192
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)
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func (gex *dhGEXSHA) Client(c packetConn, randSource io.Reader, magics *handshakeMagics) (*kexResult, error) {
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// Send GexRequest
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kexDHGexRequest := kexDHGexRequestMsg{
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MinBits: dhGroupExchangeMinimumBits,
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PreferedBits: dhGroupExchangePreferredBits,
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MaxBits: dhGroupExchangeMaximumBits,
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}
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if err := c.writePacket(Marshal(&kexDHGexRequest)); err != nil {
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return nil, err
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}
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// Receive GexGroup
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packet, err := c.readPacket()
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if err != nil {
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return nil, err
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}
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var msg kexDHGexGroupMsg
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if err = Unmarshal(packet, &msg); err != nil {
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return nil, err
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}
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// reject if p's bit length < dhGroupExchangeMinimumBits or > dhGroupExchangeMaximumBits
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if msg.P.BitLen() < dhGroupExchangeMinimumBits || msg.P.BitLen() > dhGroupExchangeMaximumBits {
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return nil, fmt.Errorf("ssh: server-generated gex p is out of range (%d bits)", msg.P.BitLen())
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}
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// Check if g is safe by verifying that 1 < g < p-1
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pMinusOne := new(big.Int).Sub(msg.P, bigOne)
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if msg.G.Cmp(bigOne) <= 0 || msg.G.Cmp(pMinusOne) >= 0 {
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return nil, fmt.Errorf("ssh: server provided gex g is not safe")
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}
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// Send GexInit
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pHalf := new(big.Int).Rsh(msg.P, 1)
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x, err := rand.Int(randSource, pHalf)
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if err != nil {
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return nil, err
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}
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X := new(big.Int).Exp(msg.G, x, msg.P)
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kexDHGexInit := kexDHGexInitMsg{
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X: X,
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}
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if err := c.writePacket(Marshal(&kexDHGexInit)); err != nil {
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return nil, err
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}
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// Receive GexReply
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packet, err = c.readPacket()
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if err != nil {
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return nil, err
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}
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var kexDHGexReply kexDHGexReplyMsg
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if err = Unmarshal(packet, &kexDHGexReply); err != nil {
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return nil, err
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}
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if kexDHGexReply.Y.Cmp(bigOne) <= 0 || kexDHGexReply.Y.Cmp(pMinusOne) >= 0 {
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return nil, errors.New("ssh: DH parameter out of bounds")
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}
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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
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if kInt.Cmp(bigOne) <= 0 || kInt.Cmp(pMinusOne) >= 0 {
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return nil, fmt.Errorf("ssh: derived k is not safe")
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}
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h := gex.hashFunc.New()
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magics.write(h)
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writeString(h, kexDHGexReply.HostKey)
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binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits))
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binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits))
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binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits))
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writeInt(h, msg.P)
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writeInt(h, msg.G)
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writeInt(h, X)
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writeInt(h, kexDHGexReply.Y)
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K := make([]byte, intLength(kInt))
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marshalInt(K, kInt)
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h.Write(K)
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return &kexResult{
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H: h.Sum(nil),
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K: K,
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HostKey: kexDHGexReply.HostKey,
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Signature: kexDHGexReply.Signature,
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Hash: gex.hashFunc,
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}, nil
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}
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// Server half implementation of the Diffie Hellman Key Exchange with SHA1 and SHA256.
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//
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// 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) {
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// Receive GexRequest
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packet, err := c.readPacket()
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if err != nil {
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return
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}
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var kexDHGexRequest kexDHGexRequestMsg
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if err = Unmarshal(packet, &kexDHGexRequest); err != nil {
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return
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}
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// Send GexGroup
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// This is the group called diffie-hellman-group14-sha1 in RFC
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// 4253 and Oakley Group 14 in RFC 3526.
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p, _ := new(big.Int).SetString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g := big.NewInt(2)
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msg := &kexDHGexGroupMsg{
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P: p,
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G: g,
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}
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if err := c.writePacket(Marshal(msg)); err != nil {
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return nil, err
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}
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// Receive GexInit
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packet, err = c.readPacket()
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if err != nil {
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return
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}
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var kexDHGexInit kexDHGexInitMsg
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if err = Unmarshal(packet, &kexDHGexInit); err != nil {
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return
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}
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pHalf := new(big.Int).Rsh(p, 1)
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y, err := rand.Int(randSource, pHalf)
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if err != nil {
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return
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}
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Y := new(big.Int).Exp(g, y, p)
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pMinusOne := new(big.Int).Sub(p, bigOne)
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if kexDHGexInit.X.Cmp(bigOne) <= 0 || kexDHGexInit.X.Cmp(pMinusOne) >= 0 {
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return nil, errors.New("ssh: DH parameter out of bounds")
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}
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kInt := new(big.Int).Exp(kexDHGexInit.X, y, p)
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hostKeyBytes := priv.PublicKey().Marshal()
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h := gex.hashFunc.New()
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magics.write(h)
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writeString(h, hostKeyBytes)
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binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMinimumBits))
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binary.Write(h, binary.BigEndian, uint32(dhGroupExchangePreferredBits))
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binary.Write(h, binary.BigEndian, uint32(dhGroupExchangeMaximumBits))
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writeInt(h, p)
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writeInt(h, g)
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writeInt(h, kexDHGexInit.X)
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writeInt(h, Y)
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K := make([]byte, intLength(kInt))
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marshalInt(K, kInt)
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h.Write(K)
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H := h.Sum(nil)
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// H is already a hash, but the hostkey signing will apply its
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// own key-specific hash algorithm.
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sig, err := signAndMarshal(priv, randSource, H, algo)
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if err != nil {
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return nil, err
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}
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kexDHGexReply := kexDHGexReplyMsg{
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HostKey: hostKeyBytes,
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Y: Y,
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Signature: sig,
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}
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packet = Marshal(&kexDHGexReply)
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err = c.writePacket(packet)
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return &kexResult{
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H: H,
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K: K,
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HostKey: hostKeyBytes,
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Signature: sig,
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Hash: gex.hashFunc,
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}, err
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}
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