xs/hkexchan.go

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package herradurakex
/* 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/aes"
"crypto/cipher"
"fmt"
"math/big"
"os"
"golang.org/x/crypto/blowfish"
"golang.org/x/crypto/twofish"
)
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// Available ciphers for hkex.Conn
const (
CAlgAES256 = iota
CAlgTwofish128 // golang.org/x/crypto/twofish
CAlgBlowfish64 // golang.org/x/crypto/blowfish
CAlgNoneDisallowed
)
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// Available HMACs for hkex.Conn (TODO: not currently used)
const (
HmacSHA256 = iota
HmacNoneDisallowed
)
type ChanOp uint8
const (
ChanOpNop = '.'
ChanOpEcho = 'e' // For testing - echo client data to stderr
//ChanOpFileWrite = "w"
//ChanOpFileRead = "r"
//ChanOpRemoteCmd = "x"
)
/*TODO: HMAC derived from HKEx FA.*/
/* Support functionality to set up encryption after a channel has
been negotiated via hkexnet.go
*/
func (hc Conn) getStream(keymat *big.Int) (ret cipher.Stream) {
var key []byte
var block cipher.Block
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]
ret = cipher.NewOFB(block, iv)
fmt.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]
ret = cipher.NewOFB(block, iv)
fmt.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]
ret = cipher.NewOFB(block, iv)
fmt.Printf("[cipher BLOWFISH_64 (%d)]\n", copts)
break
default:
fmt.Printf("DOOFUS SET A VALID CIPHER ALG (%d)\n", copts)
os.Exit(1)
}
hopts := (hc.cipheropts >> 8) & 0xFF
switch hopts {
case HmacSHA256:
fmt.Printf("[nop HmacSHA256 (%d)]\n", hopts)
break
default:
fmt.Printf("DOOFUS SET A VALID HMAC ALG (%d)\n", hopts)
os.Exit(1)
}
if err != nil {
panic(err)
}
return
}