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" "math/big" "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, 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: 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) 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 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 }