woodpecker/vendor/code.google.com/p/go.crypto/ssh/cipher.go
2015-09-29 18:21:17 -07:00

100 lines
2.9 KiB
Go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssh
import (
"crypto/aes"
"crypto/cipher"
"crypto/rc4"
)
// streamDump is used to dump the initial keystream for stream ciphers. It is a
// a write-only buffer, and not intended for reading so do not require a mutex.
var streamDump [512]byte
// noneCipher implements cipher.Stream and provides no encryption. It is used
// by the transport before the first key-exchange.
type noneCipher struct{}
func (c noneCipher) XORKeyStream(dst, src []byte) {
copy(dst, src)
}
func newAESCTR(key, iv []byte) (cipher.Stream, error) {
c, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
return cipher.NewCTR(c, iv), nil
}
func newRC4(key, iv []byte) (cipher.Stream, error) {
return rc4.NewCipher(key)
}
type cipherMode struct {
keySize int
ivSize int
skip int
createFunc func(key, iv []byte) (cipher.Stream, error)
}
func (c *cipherMode) createCipher(key, iv []byte) (cipher.Stream, error) {
if len(key) < c.keySize {
panic("ssh: key length too small for cipher")
}
if len(iv) < c.ivSize {
panic("ssh: iv too small for cipher")
}
stream, err := c.createFunc(key[:c.keySize], iv[:c.ivSize])
if err != nil {
return nil, err
}
for remainingToDump := c.skip; remainingToDump > 0; {
dumpThisTime := remainingToDump
if dumpThisTime > len(streamDump) {
dumpThisTime = len(streamDump)
}
stream.XORKeyStream(streamDump[:dumpThisTime], streamDump[:dumpThisTime])
remainingToDump -= dumpThisTime
}
return stream, nil
}
// Specifies a default set of ciphers and a preference order. This is based on
// OpenSSH's default client preference order, minus algorithms that are not
// implemented.
var DefaultCipherOrder = []string{
"aes128-ctr", "aes192-ctr", "aes256-ctr",
"arcfour256", "arcfour128",
}
// cipherModes documents properties of supported ciphers. Ciphers not included
// are not supported and will not be negotiated, even if explicitly requested in
// ClientConfig.Crypto.Ciphers.
var cipherModes = map[string]*cipherMode{
// Ciphers from RFC4344, which introduced many CTR-based ciphers. Algorithms
// are defined in the order specified in the RFC.
"aes128-ctr": {16, aes.BlockSize, 0, newAESCTR},
"aes192-ctr": {24, aes.BlockSize, 0, newAESCTR},
"aes256-ctr": {32, aes.BlockSize, 0, newAESCTR},
// Ciphers from RFC4345, which introduces security-improved arcfour ciphers.
// They are defined in the order specified in the RFC.
"arcfour128": {16, 0, 1536, newRC4},
"arcfour256": {32, 0, 1536, newRC4},
}
// defaultKeyExchangeOrder specifies a default set of key exchange algorithms
// with preferences.
var defaultKeyExchangeOrder = []string{
// P384 and P521 are not constant-time yet, but since we don't
// reuse ephemeral keys, using them for ECDH should be OK.
kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521,
kexAlgoDH14SHA1, kexAlgoDH1SHA1,
}