package hkexnet // 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" "errors" "fmt" "hash" "log" "golang.org/x/crypto/blowfish" "golang.org/x/crypto/twofish" "blitter.com/go/cryptmt" // hash algos must be manually imported thusly: // (Would be nice if the golang pkg docs were more clear // on this...) _ "crypto/sha256" _ "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. // // This is used for block ciphers; stream ciphers should do their // own key expansion. 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 */ func (hc Conn) getStream(keymat []byte) (rc cipher.Stream, mc hash.Hash, err error) { var key []byte var block cipher.Block var iv []byte var ivlen int 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: keymat = expandKeyMat(keymat, aes.BlockSize) key = keymat[0:aes.BlockSize] block, err = aes.NewCipher(key) ivlen = aes.BlockSize iv = keymat[aes.BlockSize : aes.BlockSize+ivlen] rc = cipher.NewOFB(block, iv) 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 iv = keymat[twofish.BlockSize : twofish.BlockSize+ivlen] rc = cipher.NewOFB(block, iv) 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 // 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[blowfish.BlockSize : blowfish.BlockSize+ivlen] rc = cipher.NewOFB(block, iv) log.Printf("[cipher BLOWFISH_64 (%d)]\n", copts) break case CAlgCryptMT1: rc = cryptmt.NewCipher(keymat) log.Printf("[cipher CRYPTMT1 (%d)]\n", copts) break default: log.Printf("[invalid cipher (%d)]\n", copts) fmt.Printf("DOOFUS SET A VALID CIPHER ALG (%d)\n", copts) err = errors.New("hkexchan: INVALID CIPHER ALG") //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 case HmacSHA512: log.Printf("[hash HmacSHA512 (%d)]\n", hopts) halg := crypto.SHA512 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) err = errors.New("hkexchan: INVALID HMAC ALG") return //os.Exit(1) } if err != nil { // 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 }