xs/hkexchan.go
2018-04-07 13:04:10 -07:00

128 lines
3.5 KiB
Go

package hkexsh
// Copyright (c) 2017-2018 Russell Magee
// Licensed under the terms of the MIT license (see LICENSE.mit in this
// distribution)
//
// golang implementation by Russ Magee (rmagee_at_gmail.com)
/* Support functions to set up encryption once an HKEx Conn has been
established with FA exchange and support channel operations
(echo, file-copy, remote-cmd, ...) */
import (
"crypto"
"crypto/aes"
"crypto/cipher"
"encoding/hex"
"fmt"
"hash"
"log"
"math/big"
"os"
"golang.org/x/crypto/blowfish"
"golang.org/x/crypto/twofish"
// hash algos must be manually imported thusly:
// (Would be nice if the golang pkg docs were more clear
// on this...)
_ "crypto/sha256"
)
// Available ciphers for hkex.Conn
const (
CAlgAES256 = iota
CAlgTwofish128 // golang.org/x/crypto/twofish
CAlgBlowfish64 // golang.org/x/crypto/blowfish
CAlgNoneDisallowed
)
// Available HMACs for hkex.Conn (TODO: not currently used)
const (
HmacSHA256 = iota
HmacNoneDisallowed
)
/* Support functionality to set up encryption after a channel has
been negotiated via hkexnet.go
*/
func (hc Conn) getStream(keymat *big.Int) (rc cipher.Stream, mc hash.Hash) {
var key []byte
var block cipher.Block
var iv []byte
var ivlen int
var err error
copts := hc.cipheropts & 0xFF
// TODO: each cipher alg case should ensure len(keymat.Bytes())
// is >= 2*cipher.BlockSize (enough for both key and iv)
switch copts {
case CAlgAES256:
key = keymat.Bytes()[0:aes.BlockSize]
block, err = aes.NewCipher(key)
ivlen = aes.BlockSize
iv = keymat.Bytes()[aes.BlockSize : aes.BlockSize+ivlen]
rc = cipher.NewOFB(block, iv)
log.Printf("[cipher AES_256 (%d)]\n", copts)
break
case CAlgTwofish128:
key = keymat.Bytes()[0:twofish.BlockSize]
block, err = twofish.NewCipher(key)
ivlen = twofish.BlockSize
iv = keymat.Bytes()[twofish.BlockSize : twofish.BlockSize+ivlen]
rc = cipher.NewOFB(block, iv)
log.Printf("[cipher TWOFISH_128 (%d)]\n", copts)
break
case CAlgBlowfish64:
key = keymat.Bytes()[0:blowfish.BlockSize]
block, err = blowfish.NewCipher(key)
ivlen = blowfish.BlockSize
// N.b. Bounds enforcement of differing cipher algorithms
// ------------------------------------------------------
// cipher/aes and x/cipher/twofish appear to allow one to
// pass an iv larger than the blockSize harmlessly to
// cipher.NewOFB(); x/cipher/blowfish implementation will
// segfault here if len(iv) is not exactly blowfish.BlockSize.
//
// I assume the other two check bounds and only
// copy what's needed whereas blowfish does no such check.
iv = keymat.Bytes()[blowfish.BlockSize : blowfish.BlockSize+ivlen]
rc = cipher.NewOFB(block, iv)
log.Printf("[cipher BLOWFISH_64 (%d)]\n", copts)
break
default:
log.Printf("[invalid cipher (%d)]\n", copts)
fmt.Printf("DOOFUS SET A VALID CIPHER ALG (%d)\n", copts)
os.Exit(1)
}
hopts := (hc.cipheropts >> 8) & 0xFF
switch hopts {
case HmacSHA256:
log.Printf("[hash HmacSHA256 (%d)]\n", hopts)
halg := crypto.SHA256
mc = halg.New()
if !halg.Available() {
log.Fatal("hash not available!")
}
break
default:
log.Printf("[invalid hmac (%d)]\n", hopts)
fmt.Printf("DOOFUS SET A VALID HMAC ALG (%d)\n", hopts)
os.Exit(1)
}
if err != nil {
panic(err)
}
// Feed the IV into the hmac: all traffic in the connection must
// feed its data into the hmac afterwards, so both ends can xor
// that with the stream to detect corruption.
_, _ = mc.Write(iv)
var currentHash []byte
currentHash = mc.Sum(currentHash)
log.Printf("Channel init hmac(iv):%s\n", hex.EncodeToString(currentHash))
return
}