89 строки
2.4 KiB
Go
89 строки
2.4 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/rc4"
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)
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// streamDump is used to dump the initial keystream for stream ciphers. It is a
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// a write-only buffer, and not intended for reading so do not require a mutex.
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var streamDump [512]byte
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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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skip int
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createFunc func(key, iv []byte) (cipher.Stream, error)
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}
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func (c *cipherMode) createCipher(key, iv []byte) (cipher.Stream, error) {
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if len(key) < c.keySize {
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panic("ssh: key length too small for cipher")
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}
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if len(iv) < c.ivSize {
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panic("ssh: iv too small for cipher")
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}
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stream, err := c.createFunc(key[:c.keySize], iv[:c.ivSize])
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if err != nil {
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return nil, err
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}
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for remainingToDump := c.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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return stream, nil
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}
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// Specifies a default set of ciphers and a preference order. This is based on
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// OpenSSH's default client preference order, minus algorithms that are not
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// implemented.
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var DefaultCipherOrder = []string{
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"aes128-ctr", "aes192-ctr", "aes256-ctr",
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"arcfour256", "arcfour128",
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}
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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, 0, newAESCTR},
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"aes192-ctr": {24, aes.BlockSize, 0, newAESCTR},
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"aes256-ctr": {32, aes.BlockSize, 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, 1536, newRC4},
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"arcfour256": {32, 0, 1536, newRC4},
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}
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