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771 lines
21 KiB
Go
771 lines
21 KiB
Go
// Copyright 2011 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/aes"
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"crypto/cipher"
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"crypto/des"
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"crypto/rc4"
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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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"hash"
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"io"
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"io/ioutil"
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"math/bits"
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"golang.org/x/crypto/internal/chacha20"
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"golang.org/x/crypto/poly1305"
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)
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const (
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packetSizeMultiple = 16 // TODO(huin) this should be determined by the cipher.
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// RFC 4253 section 6.1 defines a minimum packet size of 32768 that implementations
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// MUST be able to process (plus a few more kilobytes for padding and mac). The RFC
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// indicates implementations SHOULD be able to handle larger packet sizes, but then
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// waffles on about reasonable limits.
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//
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// OpenSSH caps their maxPacket at 256kB so we choose to do
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// the same. maxPacket is also used to ensure that uint32
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// length fields do not overflow, so it should remain well
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// below 4G.
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maxPacket = 256 * 1024
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)
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// noneCipher implements cipher.Stream and provides no encryption. It is used
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// by the transport before the first key-exchange.
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type noneCipher struct{}
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func (c noneCipher) XORKeyStream(dst, src []byte) {
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copy(dst, src)
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}
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func newAESCTR(key, iv []byte) (cipher.Stream, error) {
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c, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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return cipher.NewCTR(c, iv), nil
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}
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func newRC4(key, iv []byte) (cipher.Stream, error) {
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return rc4.NewCipher(key)
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}
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type cipherMode struct {
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keySize int
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ivSize int
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create func(key, iv []byte, macKey []byte, algs directionAlgorithms) (packetCipher, error)
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}
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func streamCipherMode(skip int, createFunc func(key, iv []byte) (cipher.Stream, error)) func(key, iv []byte, macKey []byte, algs directionAlgorithms) (packetCipher, error) {
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return func(key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) {
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stream, err := createFunc(key, iv)
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if err != nil {
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return nil, err
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}
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var streamDump []byte
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if skip > 0 {
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streamDump = make([]byte, 512)
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}
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for remainingToDump := skip; remainingToDump > 0; {
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dumpThisTime := remainingToDump
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if dumpThisTime > len(streamDump) {
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dumpThisTime = len(streamDump)
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}
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stream.XORKeyStream(streamDump[:dumpThisTime], streamDump[:dumpThisTime])
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remainingToDump -= dumpThisTime
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}
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mac := macModes[algs.MAC].new(macKey)
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return &streamPacketCipher{
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mac: mac,
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etm: macModes[algs.MAC].etm,
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macResult: make([]byte, mac.Size()),
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cipher: stream,
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}, nil
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}
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}
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// cipherModes documents properties of supported ciphers. Ciphers not included
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// are not supported and will not be negotiated, even if explicitly requested in
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// ClientConfig.Crypto.Ciphers.
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var cipherModes = map[string]*cipherMode{
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// Ciphers from RFC4344, which introduced many CTR-based ciphers. Algorithms
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// are defined in the order specified in the RFC.
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"aes128-ctr": {16, aes.BlockSize, streamCipherMode(0, newAESCTR)},
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"aes192-ctr": {24, aes.BlockSize, streamCipherMode(0, newAESCTR)},
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"aes256-ctr": {32, aes.BlockSize, streamCipherMode(0, newAESCTR)},
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// Ciphers from RFC4345, which introduces security-improved arcfour ciphers.
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// They are defined in the order specified in the RFC.
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"arcfour128": {16, 0, streamCipherMode(1536, newRC4)},
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"arcfour256": {32, 0, streamCipherMode(1536, newRC4)},
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// Cipher defined in RFC 4253, which describes SSH Transport Layer Protocol.
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// Note that this cipher is not safe, as stated in RFC 4253: "Arcfour (and
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// RC4) has problems with weak keys, and should be used with caution."
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// RFC4345 introduces improved versions of Arcfour.
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"arcfour": {16, 0, streamCipherMode(0, newRC4)},
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// AEAD ciphers
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gcmCipherID: {16, 12, newGCMCipher},
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chacha20Poly1305ID: {64, 0, newChaCha20Cipher},
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// CBC mode is insecure and so is not included in the default config.
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// (See http://www.isg.rhul.ac.uk/~kp/SandPfinal.pdf). If absolutely
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// needed, it's possible to specify a custom Config to enable it.
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// You should expect that an active attacker can recover plaintext if
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// you do.
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aes128cbcID: {16, aes.BlockSize, newAESCBCCipher},
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// 3des-cbc is insecure and is not included in the default
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// config.
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tripledescbcID: {24, des.BlockSize, newTripleDESCBCCipher},
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}
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// prefixLen is the length of the packet prefix that contains the packet length
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// and number of padding bytes.
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const prefixLen = 5
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// streamPacketCipher is a packetCipher using a stream cipher.
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type streamPacketCipher struct {
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mac hash.Hash
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cipher cipher.Stream
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etm bool
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// The following members are to avoid per-packet allocations.
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prefix [prefixLen]byte
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seqNumBytes [4]byte
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padding [2 * packetSizeMultiple]byte
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packetData []byte
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macResult []byte
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}
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// readCipherPacket reads and decrypt a single packet from the reader argument.
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func (s *streamPacketCipher) readCipherPacket(seqNum uint32, r io.Reader) ([]byte, error) {
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if _, err := io.ReadFull(r, s.prefix[:]); err != nil {
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return nil, err
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}
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var encryptedPaddingLength [1]byte
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if s.mac != nil && s.etm {
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copy(encryptedPaddingLength[:], s.prefix[4:5])
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s.cipher.XORKeyStream(s.prefix[4:5], s.prefix[4:5])
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} else {
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s.cipher.XORKeyStream(s.prefix[:], s.prefix[:])
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}
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length := binary.BigEndian.Uint32(s.prefix[0:4])
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paddingLength := uint32(s.prefix[4])
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var macSize uint32
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if s.mac != nil {
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s.mac.Reset()
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binary.BigEndian.PutUint32(s.seqNumBytes[:], seqNum)
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s.mac.Write(s.seqNumBytes[:])
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if s.etm {
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s.mac.Write(s.prefix[:4])
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s.mac.Write(encryptedPaddingLength[:])
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} else {
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s.mac.Write(s.prefix[:])
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}
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macSize = uint32(s.mac.Size())
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}
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if length <= paddingLength+1 {
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return nil, errors.New("ssh: invalid packet length, packet too small")
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}
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if length > maxPacket {
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return nil, errors.New("ssh: invalid packet length, packet too large")
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}
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// the maxPacket check above ensures that length-1+macSize
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// does not overflow.
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if uint32(cap(s.packetData)) < length-1+macSize {
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s.packetData = make([]byte, length-1+macSize)
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} else {
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s.packetData = s.packetData[:length-1+macSize]
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}
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if _, err := io.ReadFull(r, s.packetData); err != nil {
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return nil, err
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}
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mac := s.packetData[length-1:]
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data := s.packetData[:length-1]
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if s.mac != nil && s.etm {
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s.mac.Write(data)
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}
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s.cipher.XORKeyStream(data, data)
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if s.mac != nil {
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if !s.etm {
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s.mac.Write(data)
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}
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s.macResult = s.mac.Sum(s.macResult[:0])
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if subtle.ConstantTimeCompare(s.macResult, mac) != 1 {
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return nil, errors.New("ssh: MAC failure")
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}
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}
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return s.packetData[:length-paddingLength-1], nil
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}
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// writeCipherPacket encrypts and sends a packet of data to the writer argument
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func (s *streamPacketCipher) writeCipherPacket(seqNum uint32, w io.Writer, rand io.Reader, packet []byte) error {
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if len(packet) > maxPacket {
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return errors.New("ssh: packet too large")
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}
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aadlen := 0
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if s.mac != nil && s.etm {
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// packet length is not encrypted for EtM modes
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aadlen = 4
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}
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paddingLength := packetSizeMultiple - (prefixLen+len(packet)-aadlen)%packetSizeMultiple
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if paddingLength < 4 {
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paddingLength += packetSizeMultiple
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}
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length := len(packet) + 1 + paddingLength
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binary.BigEndian.PutUint32(s.prefix[:], uint32(length))
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s.prefix[4] = byte(paddingLength)
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padding := s.padding[:paddingLength]
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if _, err := io.ReadFull(rand, padding); err != nil {
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return err
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}
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if s.mac != nil {
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s.mac.Reset()
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binary.BigEndian.PutUint32(s.seqNumBytes[:], seqNum)
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s.mac.Write(s.seqNumBytes[:])
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if s.etm {
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// For EtM algorithms, the packet length must stay unencrypted,
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// but the following data (padding length) must be encrypted
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s.cipher.XORKeyStream(s.prefix[4:5], s.prefix[4:5])
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}
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s.mac.Write(s.prefix[:])
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if !s.etm {
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// For non-EtM algorithms, the algorithm is applied on unencrypted data
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s.mac.Write(packet)
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s.mac.Write(padding)
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}
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}
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if !(s.mac != nil && s.etm) {
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// For EtM algorithms, the padding length has already been encrypted
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// and the packet length must remain unencrypted
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s.cipher.XORKeyStream(s.prefix[:], s.prefix[:])
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}
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s.cipher.XORKeyStream(packet, packet)
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s.cipher.XORKeyStream(padding, padding)
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if s.mac != nil && s.etm {
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// For EtM algorithms, packet and padding must be encrypted
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s.mac.Write(packet)
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s.mac.Write(padding)
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}
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if _, err := w.Write(s.prefix[:]); err != nil {
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return err
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}
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if _, err := w.Write(packet); err != nil {
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return err
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}
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if _, err := w.Write(padding); err != nil {
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return err
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}
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if s.mac != nil {
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s.macResult = s.mac.Sum(s.macResult[:0])
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if _, err := w.Write(s.macResult); err != nil {
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return err
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}
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}
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return nil
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}
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type gcmCipher struct {
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aead cipher.AEAD
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prefix [4]byte
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iv []byte
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buf []byte
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}
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func newGCMCipher(key, iv, unusedMacKey []byte, unusedAlgs directionAlgorithms) (packetCipher, error) {
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c, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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aead, err := cipher.NewGCM(c)
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if err != nil {
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return nil, err
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}
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return &gcmCipher{
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aead: aead,
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iv: iv,
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}, nil
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}
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const gcmTagSize = 16
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func (c *gcmCipher) writeCipherPacket(seqNum uint32, w io.Writer, rand io.Reader, packet []byte) error {
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// Pad out to multiple of 16 bytes. This is different from the
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// stream cipher because that encrypts the length too.
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padding := byte(packetSizeMultiple - (1+len(packet))%packetSizeMultiple)
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if padding < 4 {
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padding += packetSizeMultiple
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}
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length := uint32(len(packet) + int(padding) + 1)
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binary.BigEndian.PutUint32(c.prefix[:], length)
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if _, err := w.Write(c.prefix[:]); err != nil {
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return err
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}
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if cap(c.buf) < int(length) {
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c.buf = make([]byte, length)
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} else {
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c.buf = c.buf[:length]
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}
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c.buf[0] = padding
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copy(c.buf[1:], packet)
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if _, err := io.ReadFull(rand, c.buf[1+len(packet):]); err != nil {
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return err
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}
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c.buf = c.aead.Seal(c.buf[:0], c.iv, c.buf, c.prefix[:])
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if _, err := w.Write(c.buf); err != nil {
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return err
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}
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c.incIV()
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return nil
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}
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func (c *gcmCipher) incIV() {
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for i := 4 + 7; i >= 4; i-- {
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c.iv[i]++
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if c.iv[i] != 0 {
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break
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}
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}
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}
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func (c *gcmCipher) readCipherPacket(seqNum uint32, r io.Reader) ([]byte, error) {
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if _, err := io.ReadFull(r, c.prefix[:]); err != nil {
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return nil, err
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}
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length := binary.BigEndian.Uint32(c.prefix[:])
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if length > maxPacket {
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return nil, errors.New("ssh: max packet length exceeded")
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}
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if cap(c.buf) < int(length+gcmTagSize) {
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c.buf = make([]byte, length+gcmTagSize)
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} else {
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c.buf = c.buf[:length+gcmTagSize]
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}
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if _, err := io.ReadFull(r, c.buf); err != nil {
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return nil, err
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}
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plain, err := c.aead.Open(c.buf[:0], c.iv, c.buf, c.prefix[:])
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if err != nil {
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return nil, err
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}
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c.incIV()
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padding := plain[0]
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if padding < 4 {
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// padding is a byte, so it automatically satisfies
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// the maximum size, which is 255.
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return nil, fmt.Errorf("ssh: illegal padding %d", padding)
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}
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if int(padding+1) >= len(plain) {
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return nil, fmt.Errorf("ssh: padding %d too large", padding)
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}
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plain = plain[1 : length-uint32(padding)]
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return plain, nil
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}
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// cbcCipher implements aes128-cbc cipher defined in RFC 4253 section 6.1
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type cbcCipher struct {
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mac hash.Hash
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macSize uint32
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decrypter cipher.BlockMode
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encrypter cipher.BlockMode
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// The following members are to avoid per-packet allocations.
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seqNumBytes [4]byte
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packetData []byte
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macResult []byte
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// Amount of data we should still read to hide which
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// verification error triggered.
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oracleCamouflage uint32
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}
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func newCBCCipher(c cipher.Block, key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) {
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cbc := &cbcCipher{
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mac: macModes[algs.MAC].new(macKey),
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decrypter: cipher.NewCBCDecrypter(c, iv),
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encrypter: cipher.NewCBCEncrypter(c, iv),
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packetData: make([]byte, 1024),
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}
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if cbc.mac != nil {
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cbc.macSize = uint32(cbc.mac.Size())
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}
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return cbc, nil
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}
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func newAESCBCCipher(key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) {
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c, err := aes.NewCipher(key)
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if err != nil {
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return nil, err
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}
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cbc, err := newCBCCipher(c, key, iv, macKey, algs)
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if err != nil {
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return nil, err
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}
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return cbc, nil
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}
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func newTripleDESCBCCipher(key, iv, macKey []byte, algs directionAlgorithms) (packetCipher, error) {
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c, err := des.NewTripleDESCipher(key)
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if err != nil {
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return nil, err
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}
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cbc, err := newCBCCipher(c, key, iv, macKey, algs)
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if err != nil {
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return nil, err
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}
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return cbc, nil
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}
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func maxUInt32(a, b int) uint32 {
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if a > b {
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return uint32(a)
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}
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return uint32(b)
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}
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const (
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cbcMinPacketSizeMultiple = 8
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cbcMinPacketSize = 16
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cbcMinPaddingSize = 4
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)
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// cbcError represents a verification error that may leak information.
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type cbcError string
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func (e cbcError) Error() string { return string(e) }
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func (c *cbcCipher) readCipherPacket(seqNum uint32, r io.Reader) ([]byte, error) {
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p, err := c.readCipherPacketLeaky(seqNum, r)
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if err != nil {
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if _, ok := err.(cbcError); ok {
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// Verification error: read a fixed amount of
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// data, to make distinguishing between
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// failing MAC and failing length check more
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// difficult.
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io.CopyN(ioutil.Discard, r, int64(c.oracleCamouflage))
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}
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}
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return p, err
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}
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func (c *cbcCipher) readCipherPacketLeaky(seqNum uint32, r io.Reader) ([]byte, error) {
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blockSize := c.decrypter.BlockSize()
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// Read the header, which will include some of the subsequent data in the
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// case of block ciphers - this is copied back to the payload later.
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// How many bytes of payload/padding will be read with this first read.
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firstBlockLength := uint32((prefixLen + blockSize - 1) / blockSize * blockSize)
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firstBlock := c.packetData[:firstBlockLength]
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if _, err := io.ReadFull(r, firstBlock); err != nil {
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return nil, err
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}
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c.oracleCamouflage = maxPacket + 4 + c.macSize - firstBlockLength
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c.decrypter.CryptBlocks(firstBlock, firstBlock)
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length := binary.BigEndian.Uint32(firstBlock[:4])
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if length > maxPacket {
|
|
return nil, cbcError("ssh: packet too large")
|
|
}
|
|
if length+4 < maxUInt32(cbcMinPacketSize, blockSize) {
|
|
// The minimum size of a packet is 16 (or the cipher block size, whichever
|
|
// is larger) bytes.
|
|
return nil, cbcError("ssh: packet too small")
|
|
}
|
|
// The length of the packet (including the length field but not the MAC) must
|
|
// be a multiple of the block size or 8, whichever is larger.
|
|
if (length+4)%maxUInt32(cbcMinPacketSizeMultiple, blockSize) != 0 {
|
|
return nil, cbcError("ssh: invalid packet length multiple")
|
|
}
|
|
|
|
paddingLength := uint32(firstBlock[4])
|
|
if paddingLength < cbcMinPaddingSize || length <= paddingLength+1 {
|
|
return nil, cbcError("ssh: invalid packet length")
|
|
}
|
|
|
|
// Positions within the c.packetData buffer:
|
|
macStart := 4 + length
|
|
paddingStart := macStart - paddingLength
|
|
|
|
// Entire packet size, starting before length, ending at end of mac.
|
|
entirePacketSize := macStart + c.macSize
|
|
|
|
// Ensure c.packetData is large enough for the entire packet data.
|
|
if uint32(cap(c.packetData)) < entirePacketSize {
|
|
// Still need to upsize and copy, but this should be rare at runtime, only
|
|
// on upsizing the packetData buffer.
|
|
c.packetData = make([]byte, entirePacketSize)
|
|
copy(c.packetData, firstBlock)
|
|
} else {
|
|
c.packetData = c.packetData[:entirePacketSize]
|
|
}
|
|
|
|
n, err := io.ReadFull(r, c.packetData[firstBlockLength:])
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
c.oracleCamouflage -= uint32(n)
|
|
|
|
remainingCrypted := c.packetData[firstBlockLength:macStart]
|
|
c.decrypter.CryptBlocks(remainingCrypted, remainingCrypted)
|
|
|
|
mac := c.packetData[macStart:]
|
|
if c.mac != nil {
|
|
c.mac.Reset()
|
|
binary.BigEndian.PutUint32(c.seqNumBytes[:], seqNum)
|
|
c.mac.Write(c.seqNumBytes[:])
|
|
c.mac.Write(c.packetData[:macStart])
|
|
c.macResult = c.mac.Sum(c.macResult[:0])
|
|
if subtle.ConstantTimeCompare(c.macResult, mac) != 1 {
|
|
return nil, cbcError("ssh: MAC failure")
|
|
}
|
|
}
|
|
|
|
return c.packetData[prefixLen:paddingStart], nil
|
|
}
|
|
|
|
func (c *cbcCipher) writeCipherPacket(seqNum uint32, w io.Writer, rand io.Reader, packet []byte) error {
|
|
effectiveBlockSize := maxUInt32(cbcMinPacketSizeMultiple, c.encrypter.BlockSize())
|
|
|
|
// Length of encrypted portion of the packet (header, payload, padding).
|
|
// Enforce minimum padding and packet size.
|
|
encLength := maxUInt32(prefixLen+len(packet)+cbcMinPaddingSize, cbcMinPaddingSize)
|
|
// Enforce block size.
|
|
encLength = (encLength + effectiveBlockSize - 1) / effectiveBlockSize * effectiveBlockSize
|
|
|
|
length := encLength - 4
|
|
paddingLength := int(length) - (1 + len(packet))
|
|
|
|
// Overall buffer contains: header, payload, padding, mac.
|
|
// Space for the MAC is reserved in the capacity but not the slice length.
|
|
bufferSize := encLength + c.macSize
|
|
if uint32(cap(c.packetData)) < bufferSize {
|
|
c.packetData = make([]byte, encLength, bufferSize)
|
|
} else {
|
|
c.packetData = c.packetData[:encLength]
|
|
}
|
|
|
|
p := c.packetData
|
|
|
|
// Packet header.
|
|
binary.BigEndian.PutUint32(p, length)
|
|
p = p[4:]
|
|
p[0] = byte(paddingLength)
|
|
|
|
// Payload.
|
|
p = p[1:]
|
|
copy(p, packet)
|
|
|
|
// Padding.
|
|
p = p[len(packet):]
|
|
if _, err := io.ReadFull(rand, p); err != nil {
|
|
return err
|
|
}
|
|
|
|
if c.mac != nil {
|
|
c.mac.Reset()
|
|
binary.BigEndian.PutUint32(c.seqNumBytes[:], seqNum)
|
|
c.mac.Write(c.seqNumBytes[:])
|
|
c.mac.Write(c.packetData)
|
|
// The MAC is now appended into the capacity reserved for it earlier.
|
|
c.packetData = c.mac.Sum(c.packetData)
|
|
}
|
|
|
|
c.encrypter.CryptBlocks(c.packetData[:encLength], c.packetData[:encLength])
|
|
|
|
if _, err := w.Write(c.packetData); err != nil {
|
|
return err
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
const chacha20Poly1305ID = "chacha20-poly1305@openssh.com"
|
|
|
|
// chacha20Poly1305Cipher implements the chacha20-poly1305@openssh.com
|
|
// AEAD, which is described here:
|
|
//
|
|
// https://tools.ietf.org/html/draft-josefsson-ssh-chacha20-poly1305-openssh-00
|
|
//
|
|
// the methods here also implement padding, which RFC4253 Section 6
|
|
// also requires of stream ciphers.
|
|
type chacha20Poly1305Cipher struct {
|
|
lengthKey [8]uint32
|
|
contentKey [8]uint32
|
|
buf []byte
|
|
}
|
|
|
|
func newChaCha20Cipher(key, unusedIV, unusedMACKey []byte, unusedAlgs directionAlgorithms) (packetCipher, error) {
|
|
if len(key) != 64 {
|
|
panic(len(key))
|
|
}
|
|
|
|
c := &chacha20Poly1305Cipher{
|
|
buf: make([]byte, 256),
|
|
}
|
|
|
|
for i := range c.contentKey {
|
|
c.contentKey[i] = binary.LittleEndian.Uint32(key[i*4 : (i+1)*4])
|
|
}
|
|
for i := range c.lengthKey {
|
|
c.lengthKey[i] = binary.LittleEndian.Uint32(key[(i+8)*4 : (i+9)*4])
|
|
}
|
|
return c, nil
|
|
}
|
|
|
|
func (c *chacha20Poly1305Cipher) readCipherPacket(seqNum uint32, r io.Reader) ([]byte, error) {
|
|
nonce := [3]uint32{0, 0, bits.ReverseBytes32(seqNum)}
|
|
s := chacha20.New(c.contentKey, nonce)
|
|
var polyKey [32]byte
|
|
s.XORKeyStream(polyKey[:], polyKey[:])
|
|
s.Advance() // skip next 32 bytes
|
|
|
|
encryptedLength := c.buf[:4]
|
|
if _, err := io.ReadFull(r, encryptedLength); err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
var lenBytes [4]byte
|
|
chacha20.New(c.lengthKey, nonce).XORKeyStream(lenBytes[:], encryptedLength)
|
|
|
|
length := binary.BigEndian.Uint32(lenBytes[:])
|
|
if length > maxPacket {
|
|
return nil, errors.New("ssh: invalid packet length, packet too large")
|
|
}
|
|
|
|
contentEnd := 4 + length
|
|
packetEnd := contentEnd + poly1305.TagSize
|
|
if uint32(cap(c.buf)) < packetEnd {
|
|
c.buf = make([]byte, packetEnd)
|
|
copy(c.buf[:], encryptedLength)
|
|
} else {
|
|
c.buf = c.buf[:packetEnd]
|
|
}
|
|
|
|
if _, err := io.ReadFull(r, c.buf[4:packetEnd]); err != nil {
|
|
return nil, err
|
|
}
|
|
|
|
var mac [poly1305.TagSize]byte
|
|
copy(mac[:], c.buf[contentEnd:packetEnd])
|
|
if !poly1305.Verify(&mac, c.buf[:contentEnd], &polyKey) {
|
|
return nil, errors.New("ssh: MAC failure")
|
|
}
|
|
|
|
plain := c.buf[4:contentEnd]
|
|
s.XORKeyStream(plain, plain)
|
|
|
|
padding := plain[0]
|
|
if padding < 4 {
|
|
// padding is a byte, so it automatically satisfies
|
|
// the maximum size, which is 255.
|
|
return nil, fmt.Errorf("ssh: illegal padding %d", padding)
|
|
}
|
|
|
|
if int(padding)+1 >= len(plain) {
|
|
return nil, fmt.Errorf("ssh: padding %d too large", padding)
|
|
}
|
|
|
|
plain = plain[1 : len(plain)-int(padding)]
|
|
|
|
return plain, nil
|
|
}
|
|
|
|
func (c *chacha20Poly1305Cipher) writeCipherPacket(seqNum uint32, w io.Writer, rand io.Reader, payload []byte) error {
|
|
nonce := [3]uint32{0, 0, bits.ReverseBytes32(seqNum)}
|
|
s := chacha20.New(c.contentKey, nonce)
|
|
var polyKey [32]byte
|
|
s.XORKeyStream(polyKey[:], polyKey[:])
|
|
s.Advance() // skip next 32 bytes
|
|
|
|
// There is no blocksize, so fall back to multiple of 8 byte
|
|
// padding, as described in RFC 4253, Sec 6.
|
|
const packetSizeMultiple = 8
|
|
|
|
padding := packetSizeMultiple - (1+len(payload))%packetSizeMultiple
|
|
if padding < 4 {
|
|
padding += packetSizeMultiple
|
|
}
|
|
|
|
// size (4 bytes), padding (1), payload, padding, tag.
|
|
totalLength := 4 + 1 + len(payload) + padding + poly1305.TagSize
|
|
if cap(c.buf) < totalLength {
|
|
c.buf = make([]byte, totalLength)
|
|
} else {
|
|
c.buf = c.buf[:totalLength]
|
|
}
|
|
|
|
binary.BigEndian.PutUint32(c.buf, uint32(1+len(payload)+padding))
|
|
chacha20.New(c.lengthKey, nonce).XORKeyStream(c.buf, c.buf[:4])
|
|
c.buf[4] = byte(padding)
|
|
copy(c.buf[5:], payload)
|
|
packetEnd := 5 + len(payload) + padding
|
|
if _, err := io.ReadFull(rand, c.buf[5+len(payload):packetEnd]); err != nil {
|
|
return err
|
|
}
|
|
|
|
s.XORKeyStream(c.buf[4:], c.buf[4:packetEnd])
|
|
|
|
var mac [poly1305.TagSize]byte
|
|
poly1305.Sum(&mac, c.buf[:packetEnd], &polyKey)
|
|
|
|
copy(c.buf[packetEnd:], mac[:])
|
|
|
|
if _, err := w.Write(c.buf); err != nil {
|
|
return err
|
|
}
|
|
return nil
|
|
}
|