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Minimal hmac channel verification w/close on tampering

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This commit is contained in:
Russ Magee 2018-04-15 12:58:24 -07:00
parent 351f58b6c5
commit b45784e07b
2 changed files with 20 additions and 19 deletions
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34
hkexnet.go
View file

@ -298,10 +298,10 @@ func (c Conn) Read(b []byte) (n int, err error) {
break break
} }
var hmacIn uint8 var hmacIn [4]uint8
var payloadLen uint32 var payloadLen uint32
// Read the hmac LSB and payload len first // Read the hmac and payload len first
err = binary.Read(c.c, binary.BigEndian, &hmacIn) err = binary.Read(c.c, binary.BigEndian, &hmacIn)
// Normal client 'exit' from interactive session will cause // Normal client 'exit' from interactive session will cause
// (on server side) err.Error() == "<iface/addr info ...>: use of closed network connection" // (on server side) err.Error() == "<iface/addr info ...>: use of closed network connection"
@ -314,14 +314,6 @@ func (c Conn) Read(b []byte) (n int, err error) {
return 0, err return 0, err
} }
//if err != nil {
// if err.Error() != "EOF" {
// log.Println("Error was:", err.Error())
// } else {
// return 0, err
// }
//}
err = binary.Read(c.c, binary.BigEndian, &payloadLen) err = binary.Read(c.c, binary.BigEndian, &payloadLen)
if err != nil { if err != nil {
if err.Error() != "EOF" { if err.Error() != "EOF" {
@ -348,7 +340,7 @@ func (c Conn) Read(b []byte) (n int, err error) {
} }
} }
log.Printf(" <:ctext:\r\n%s\r\n", hex.Dump(payloadBytes[:n])) //EncodeToString(b[:n])) // print only used portion log.Printf(" <:ctext:\r\n%s\r\n", hex.Dump(payloadBytes[:n]))
db := bytes.NewBuffer(payloadBytes[:n]) //copying payloadBytes to db db := bytes.NewBuffer(payloadBytes[:n]) //copying payloadBytes to db
// The StreamReader acts like a pipe, decrypting // The StreamReader acts like a pipe, decrypting
@ -358,7 +350,7 @@ func (c Conn) Read(b []byte) (n int, err error) {
// The caller isn't necessarily reading the full payload so we need // The caller isn't necessarily reading the full payload so we need
// to decrypt ot an intermediate buffer, draining it on demand of caller // to decrypt ot an intermediate buffer, draining it on demand of caller
decryptN, err := rs.Read(payloadBytes) decryptN, err := rs.Read(payloadBytes)
log.Printf(" <-ptext:\r\n%s\r\n", hex.Dump(payloadBytes[:n])) //EncodeToString(b[:n])) log.Printf(" <-ptext:\r\n%s\r\n", hex.Dump(payloadBytes[:n]))
if err != nil { if err != nil {
panic(err) panic(err)
} }
@ -367,8 +359,14 @@ func (c Conn) Read(b []byte) (n int, err error) {
// Re-calculate hmac, compare with received value // Re-calculate hmac, compare with received value
c.rm.Write(payloadBytes) c.rm.Write(payloadBytes)
hTmp := c.rm.Sum(nil)[0] hTmp := c.rm.Sum(nil)[0:4]
log.Printf("<%04x) HMAC:(i)%02x (c)%02x\r\n", decryptN, hmacIn, hTmp) log.Printf("<%04x) HMAC:(i)%s (c)%02x\r\n", decryptN, hex.EncodeToString([]byte(hmacIn[0:])), hTmp)
// Puke if hmac didn't match, corrupted channel
if !bytes.Equal(hTmp, []byte(hmacIn[0:])) || hmacIn[0] > 0xf8 {
fmt.Println("** ALERT - hmac mismatch, possible channel tampering **")
c.Close()
}
} }
retN := c.dBuf.Len() retN := c.dBuf.Len()
if retN > len(b) { if retN > len(b) {
@ -386,18 +384,18 @@ func (c Conn) Read(b []byte) (n int, err error) {
// See go doc io.Writer // See go doc io.Writer
func (c Conn) Write(b []byte) (n int, err error) { func (c Conn) Write(b []byte) (n int, err error) {
//log.Printf("[Encrypting...]\r\n") //log.Printf("[Encrypting...]\r\n")
var hmacOut uint8 var hmacOut []uint8
var payloadLen uint32 var payloadLen uint32
log.Printf(" :>ptext:\r\n%s\r\n", hex.Dump(b)) //EncodeToString(b)) log.Printf(" :>ptext:\r\n%s\r\n", hex.Dump(b))
payloadLen = uint32(len(b)) payloadLen = uint32(len(b))
// Calculate hmac on payload // Calculate hmac on payload
c.wm.Write(b) c.wm.Write(b)
hmacOut = uint8(c.wm.Sum(nil)[0]) hmacOut = c.wm.Sum(nil)[0:4]
log.Printf(" (%04x> HMAC(o):%02x\r\n", payloadLen, hmacOut) log.Printf(" (%04x> HMAC(o):%s\r\n", payloadLen, hex.EncodeToString(hmacOut))
var wb bytes.Buffer var wb bytes.Buffer
// The StreamWriter acts like a pipe, forwarding whatever is // The StreamWriter acts like a pipe, forwarding whatever is

5
hkexsh/hkexsh.go
View file

@ -80,8 +80,9 @@ func main() {
// Set stdin in raw mode if it's an interactive session // Set stdin in raw mode if it's an interactive session
// TODO: send flag to server side indicating this // TODO: send flag to server side indicating this
// affects shell command used // affects shell command used
var oldState *hkexsh.State
if isatty.IsTerminal(os.Stdin.Fd()) { if isatty.IsTerminal(os.Stdin.Fd()) {
oldState, err := hkexsh.MakeRaw(int(os.Stdin.Fd())) oldState, err = hkexsh.MakeRaw(int(os.Stdin.Fd()))
if err != nil { if err != nil {
panic(err) panic(err)
} }
@ -155,6 +156,7 @@ func main() {
if inerr != nil { if inerr != nil {
if inerr.Error() != "EOF" { if inerr.Error() != "EOF" {
fmt.Println(inerr) fmt.Println(inerr)
_ = hkexsh.Restore(int(os.Stdin.Fd()), oldState) // Best effort.
os.Exit(1) os.Exit(1)
} }
} }
@ -178,6 +180,7 @@ func main() {
log.Println(outerr) log.Println(outerr)
if outerr.Error() != "EOF" { if outerr.Error() != "EOF" {
fmt.Println(outerr) fmt.Println(outerr)
_ = hkexsh.Restore(int(os.Stdin.Fd()), oldState) // Best effort.
os.Exit(2) os.Exit(2)
} }
} }