-Added client -c option to pass cipher alg

-Note about blowfish iv len (lack of) bounds check in .NewOFB();
-TODO added to enforce keymat from HKex >= 2*chosen cipher blocksize
 (assuming keylen == blocksize -- might not be true for all future algs)

demo/client.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"flag"
 	"fmt"
 
 	hkex "blitter.com/herradurakex"
@@ -13,7 +14,12 @@ import (
 // encrypt/decrypt is done within the type.
 // Compare to 'clientp.go' in this directory to see the equivalence.
 func main() {
-	conn, err := hkex.Dial("tcp", "localhost:2000", "C_TWOFISH_128")
+	var cAlg string
+
+	flag.StringVar(&cAlg, "c", "C_AES_256", "cipher [\"C_AES_256\" | \"C_TWOFISH_128\" | \"C_BLOWFISH_64\"]")
+	flag.Parse()
+
+	conn, err := hkex.Dial("tcp", "localhost:2000", cAlg)
 	if err != nil {
 		// handle error
 		fmt.Println("Err!")

hkexchan.go

@@ -28,6 +28,7 @@ import (
 	"math/big"
 	"os"
 
+	"golang.org/x/crypto/blowfish"
 	"golang.org/x/crypto/twofish"
 )
 
@@ -35,6 +36,7 @@ import (
 const (
 	C_AES_256     = iota
 	C_TWOFISH_128 // golang.org/x/crypto/twofish
+	C_BLOWFISH_64 // golang.org/x/crypto/blowfish
 	C_NONE_DISALLOWED
 )
 
@@ -52,31 +54,48 @@ 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 C_AES_256:
 		key = keymat.Bytes()[0:aes.BlockSize]
 		block, err = aes.NewCipher(key)
+		ivlen = aes.BlockSize
 		iv := make([]byte, aes.BlockSize)
-		//if _, err = io.ReadFull(crand.Reader, iv); err != nil {
+		iv = keymat.Bytes()[aes.BlockSize : aes.BlockSize+ivlen]
-		//	panic(err)
-		//}
-		iv = keymat.Bytes()[aes.BlockSize:]
 		ret = cipher.NewOFB(block, iv)
 		fmt.Printf("[cipher AES_256 (%d)]\n", copts)
 		break
 	case C_TWOFISH_128:
 		key = keymat.Bytes()[0:twofish.BlockSize]
 		block, err = twofish.NewCipher(key)
+		ivlen = twofish.BlockSize
 		iv := make([]byte, twofish.BlockSize)
-		//if _, err = io.ReadFull(crand.Reader, iv); err != nil {
+		iv = keymat.Bytes()[twofish.BlockSize : twofish.BlockSize+ivlen]
-		//	panic(err)
-		//}
-		iv = keymat.Bytes()[twofish.BlockSize:]
 		ret = cipher.NewOFB(block, iv)
-		fmt.Printf("[cipher TWOFISH_256 (%d)]\n", copts)
+		fmt.Printf("[cipher TWOFISH_128 (%d)]\n", copts)
+		break
+	case C_BLOWFISH_64:
+		key = keymat.Bytes()[0:blowfish.BlockSize]
+		block, err = blowfish.NewCipher(key)
+		ivlen = blowfish.BlockSize
+		iv := make([]byte, 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)

hkexnet.go

@@ -89,6 +89,11 @@ func (hc *Conn) applyConnExtensions(extensions ...string) {
 			hc.cipheropts &= (0xFFFFFF00)
 			hc.cipheropts |= C_TWOFISH_128
 			break
+		case "C_BLOWFISH_64":
+			fmt.Println("[extension arg = C_BLOWFISH_64]")
+			hc.cipheropts &= (0xFFFFFF00)
+			hc.cipheropts |= C_BLOWFISH_64
+			break
 		case "H_SHA256":
 			hc.cipheropts &= (0xFFFF00FF)
 			hc.cipheropts |= (H_SHA256 << 8)