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Security: Padding done right #33

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Security: Padding done right #33

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d2b4780
Padding
Opensourcecommunitydevelopment Jul 31, 2017
618ab8e
Update gdns.go
Opensourcecommunitydevelopment Jul 31, 2017
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20 changes: 19 additions & 1 deletion gdns.go
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,18 @@ func (R *Gdns) worker(server string) {
}
}

// To prevent misinterpretation of the URL, restrict the padding characters to the unreserved URL characters:
// upper- and lower-case letters, digits, hyphen, period, underscore and tilde. http://stackoverflow.com/a/695469/18829
const padChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._~"

func getPaddedStr(n int) string {
s := make([]byte, n)
for i := range s {
s[i] = padChars[rand.Intn(len(padChars))]
}
return string(s)
}

func (R *Gdns) resolve(https *Https, server string, qname string, qtype int) *Reply {
r := Reply{ Status: -1 }
v := url.Values{}
Expand All @@ -80,7 +92,9 @@ func (R *Gdns) resolve(https *Https, server string, qname string, qtype int) *Re
v.Set("edns_client_subnet", *R.edns)
}
if !*R.nopad {
v.Set("random_padding", strings.Repeat(string(65+rand.Intn(26)), rand.Intn(500)))
// maximum dnslength+type.length (longest possible Type 5 digits)
// minus current to make always equal query lenght url
v.Set("random_padding", getPaddedStr(259-len(qname)-len(fmt.Sprintf("%d", qtype))))
}

/* query */
Expand All @@ -96,3 +110,7 @@ func (R *Gdns) resolve(https *Https, server string, qname string, qtype int) *Re

/* register module */
var _ = register("gdns", new(Gdns))

func initRand() {
rand.Seed(time.Now().UnixNano())
}