1// Copyright 2012 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5// Package xsrftoken provides methods for generating and validating secure XSRF tokens. 6package xsrftoken // import "golang.org/x/net/xsrftoken" 7 8import ( 9 "crypto/hmac" 10 "crypto/sha1" 11 "crypto/subtle" 12 "encoding/base64" 13 "fmt" 14 "strconv" 15 "strings" 16 "time" 17) 18 19// Timeout is the duration for which XSRF tokens are valid. 20// It is exported so clients may set cookie timeouts that match generated tokens. 21const Timeout = 24 * time.Hour 22 23// clean sanitizes a string for inclusion in a token by replacing all ":"s. 24func clean(s string) string { 25 return strings.Replace(s, ":", "_", -1) 26} 27 28// Generate returns a URL-safe secure XSRF token that expires in 24 hours. 29// 30// key is a secret key for your application; it must be non-empty. 31// userID is an optional unique identifier for the user. 32// actionID is an optional action the user is taking (e.g. POSTing to a particular path). 33func Generate(key, userID, actionID string) string { 34 return generateTokenAtTime(key, userID, actionID, time.Now()) 35} 36 37// generateTokenAtTime is like Generate, but returns a token that expires 24 hours from now. 38func generateTokenAtTime(key, userID, actionID string, now time.Time) string { 39 if len(key) == 0 { 40 panic("zero length xsrf secret key") 41 } 42 // Round time up and convert to milliseconds. 43 milliTime := (now.UnixNano() + 1e6 - 1) / 1e6 44 45 h := hmac.New(sha1.New, []byte(key)) 46 fmt.Fprintf(h, "%s:%s:%d", clean(userID), clean(actionID), milliTime) 47 48 // Get the padded base64 string then removing the padding. 49 tok := string(h.Sum(nil)) 50 tok = base64.URLEncoding.EncodeToString([]byte(tok)) 51 tok = strings.TrimRight(tok, "=") 52 53 return fmt.Sprintf("%s:%d", tok, milliTime) 54} 55 56// Valid reports whether a token is a valid, unexpired token returned by Generate. 57func Valid(token, key, userID, actionID string) bool { 58 return validTokenAtTime(token, key, userID, actionID, time.Now()) 59} 60 61// validTokenAtTime reports whether a token is valid at the given time. 62func validTokenAtTime(token, key, userID, actionID string, now time.Time) bool { 63 if len(key) == 0 { 64 panic("zero length xsrf secret key") 65 } 66 // Extract the issue time of the token. 67 sep := strings.LastIndex(token, ":") 68 if sep < 0 { 69 return false 70 } 71 millis, err := strconv.ParseInt(token[sep+1:], 10, 64) 72 if err != nil { 73 return false 74 } 75 issueTime := time.Unix(0, millis*1e6) 76 77 // Check that the token is not expired. 78 if now.Sub(issueTime) >= Timeout { 79 return false 80 } 81 82 // Check that the token is not from the future. 83 // Allow 1 minute grace period in case the token is being verified on a 84 // machine whose clock is behind the machine that issued the token. 85 if issueTime.After(now.Add(1 * time.Minute)) { 86 return false 87 } 88 89 expected := generateTokenAtTime(key, userID, actionID, issueTime) 90 91 // Check that the token matches the expected value. 92 // Use constant time comparison to avoid timing attacks. 93 return subtle.ConstantTimeCompare([]byte(token), []byte(expected)) == 1 94} 95