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Added keymat expansion for smallest KEX modes 

Signed-off-by: Russ Magee <rmagee@gmail.com>
This commit is contained in:
Russ Magee 2018-10-19 13:51:57 -07:00
parent 798661a0cf
commit 3991fc5065
1 changed files with 24 additions and 0 deletions
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24
hkexnet/hkexchan.go
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@ -29,6 +29,27 @@ import (
_ "crypto/sha512"
)
// Expand keymat, if necessary, to a minimum of 2x(blocksize).
// Keymat is used for initial key and the IV, hence the 2x.
// This is occasionally necessary for smaller modes of KEX algorithms
// (eg., KEX_HERRADURA256); perhaps an indication these should be
// avoided in favour of larger modes.
func expandKeyMat(keymat []byte, blocksize int) []byte {
if len(keymat) < 2*blocksize {
halg := crypto.SHA256
mc := halg.New()
if !halg.Available() {
log.Fatal("hash not available!")
}
_, _ = mc.Write(keymat)
var xpand []byte
xpand = mc.Sum(xpand)
keymat = append(keymat, xpand...)
log.Println("[NOTE: keymat short - applying key expansion using SHA256]")
}
return keymat
}
/* Support functionality to set up encryption after a channel has
been negotiated via hkexnet.go
*/
@ -43,6 +64,7 @@ func (hc Conn) getStream(keymat []byte) (rc cipher.Stream, mc hash.Hash, err err
// is >= 2*cipher.BlockSize (enough for both key and iv)
switch copts {
case CAlgAES256:
keymat = expandKeyMat(keymat, aes.BlockSize)
key = keymat[0:aes.BlockSize]
block, err = aes.NewCipher(key)
ivlen = aes.BlockSize
@ -51,6 +73,7 @@ func (hc Conn) getStream(keymat []byte) (rc cipher.Stream, mc hash.Hash, err err
log.Printf("[cipher AES_256 (%d)]\n", copts)
break
case CAlgTwofish128:
keymat = expandKeyMat(keymat, twofish.BlockSize)
key = keymat[0:twofish.BlockSize]
block, err = twofish.NewCipher(key)
ivlen = twofish.BlockSize
@ -59,6 +82,7 @@ func (hc Conn) getStream(keymat []byte) (rc cipher.Stream, mc hash.Hash, err err
log.Printf("[cipher TWOFISH_128 (%d)]\n", copts)
break
case CAlgBlowfish64:
keymat = expandKeyMat(keymat, blowfish.BlockSize)
key = keymat[0:blowfish.BlockSize]
block, err = blowfish.NewCipher(key)
ivlen = blowfish.BlockSize