ad57a9391f
- Changed from using string == to hmac.Equal - See more details here: http://verboselogging.com/2012/08/20/a-timing-attack-in-action
62 lines
1.5 KiB
Go
62 lines
1.5 KiB
Go
package main
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import (
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"crypto/hmac"
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"crypto/sha1"
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"encoding/base64"
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"fmt"
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"net/http"
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"strconv"
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"strings"
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"time"
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)
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func validateCookie(cookie *http.Cookie, seed string) (string, bool) {
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// value, timestamp, sig
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parts := strings.Split(cookie.Value, "|")
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if len(parts) != 3 {
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return "", false
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}
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sig := cookieSignature(seed, cookie.Name, parts[0], parts[1])
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if checkHmac(parts[2], sig) {
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ts, err := strconv.Atoi(parts[1])
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if err == nil && int64(ts) > time.Now().Add(time.Duration(24)*7*time.Hour*-1).Unix() {
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// it's a valid cookie. now get the contents
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rawValue, err := base64.URLEncoding.DecodeString(parts[0])
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if err == nil {
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return string(rawValue), true
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}
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}
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}
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return "", false
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}
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func signedCookieValue(seed string, key string, value string) string {
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encodedValue := base64.URLEncoding.EncodeToString([]byte(value))
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timeStr := fmt.Sprintf("%d", time.Now().Unix())
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sig := cookieSignature(seed, key, encodedValue, timeStr)
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cookieVal := fmt.Sprintf("%s|%s|%s", encodedValue, timeStr, sig)
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return cookieVal
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}
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func cookieSignature(args ...string) string {
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h := hmac.New(sha1.New, []byte(args[0]))
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for _, arg := range args[1:] {
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h.Write([]byte(arg))
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}
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var b []byte
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b = h.Sum(b)
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return base64.URLEncoding.EncodeToString(b)
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}
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func checkHmac(input, expected string) bool {
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inputMAC, err1 := base64.URLEncoding.DecodeString(input)
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if err1 == nil {
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expectedMAC, err2 := base64.URLEncoding.DecodeString(expected)
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if err2 == nil {
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return hmac.Equal(inputMAC, expectedMAC)
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}
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}
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return false
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}
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