141 lines
4.0 KiB
Go
141 lines
4.0 KiB
Go
package encryption
|
|
|
|
import (
|
|
"crypto/aes"
|
|
"crypto/cipher"
|
|
"crypto/hmac"
|
|
"crypto/rand"
|
|
"crypto/sha1"
|
|
"crypto/sha256"
|
|
"encoding/base64"
|
|
"fmt"
|
|
"hash"
|
|
"io"
|
|
"net/http"
|
|
"strconv"
|
|
"strings"
|
|
"time"
|
|
)
|
|
|
|
// cookies are stored in a 3 part (value + timestamp + signature) to enforce that the values are as originally set.
|
|
// additionally, the 'value' is encrypted so it's opaque to the browser
|
|
|
|
// Validate ensures a cookie is properly signed
|
|
func Validate(cookie *http.Cookie, seed string, expiration time.Duration) (value string, t time.Time, ok bool) {
|
|
// value, timestamp, sig
|
|
parts := strings.Split(cookie.Value, "|")
|
|
if len(parts) != 3 {
|
|
return
|
|
}
|
|
if checkSignature(parts[2], seed, cookie.Name, parts[0], parts[1]) {
|
|
ts, err := strconv.Atoi(parts[1])
|
|
if err != nil {
|
|
return
|
|
}
|
|
// The expiration timestamp set when the cookie was created
|
|
// isn't sent back by the browser. Hence, we check whether the
|
|
// creation timestamp stored in the cookie falls within the
|
|
// window defined by (Now()-expiration, Now()].
|
|
t = time.Unix(int64(ts), 0)
|
|
if t.After(time.Now().Add(expiration*-1)) && t.Before(time.Now().Add(time.Minute*5)) {
|
|
// it's a valid cookie. now get the contents
|
|
rawValue, err := base64.URLEncoding.DecodeString(parts[0])
|
|
if err == nil {
|
|
value = string(rawValue)
|
|
ok = true
|
|
return
|
|
}
|
|
}
|
|
}
|
|
return
|
|
}
|
|
|
|
// SignedValue returns a cookie that is signed and can later be checked with Validate
|
|
func SignedValue(seed string, key string, value string, now time.Time) string {
|
|
encodedValue := base64.URLEncoding.EncodeToString([]byte(value))
|
|
timeStr := fmt.Sprintf("%d", now.Unix())
|
|
sig := cookieSignature(sha256.New, seed, key, encodedValue, timeStr)
|
|
cookieVal := fmt.Sprintf("%s|%s|%s", encodedValue, timeStr, sig)
|
|
return cookieVal
|
|
}
|
|
|
|
func cookieSignature(signer func() hash.Hash, args ...string) string {
|
|
h := hmac.New(signer, []byte(args[0]))
|
|
for _, arg := range args[1:] {
|
|
h.Write([]byte(arg))
|
|
}
|
|
var b []byte
|
|
b = h.Sum(b)
|
|
return base64.URLEncoding.EncodeToString(b)
|
|
}
|
|
|
|
func checkSignature(signature string, args ...string) bool {
|
|
checkSig := cookieSignature(sha256.New, args...)
|
|
if checkHmac(signature, checkSig) {
|
|
return true
|
|
}
|
|
|
|
// TODO: After appropriate rollout window, remove support for SHA1
|
|
legacySig := cookieSignature(sha1.New, args...)
|
|
return checkHmac(signature, legacySig)
|
|
}
|
|
|
|
func checkHmac(input, expected string) bool {
|
|
inputMAC, err1 := base64.URLEncoding.DecodeString(input)
|
|
if err1 == nil {
|
|
expectedMAC, err2 := base64.URLEncoding.DecodeString(expected)
|
|
if err2 == nil {
|
|
return hmac.Equal(inputMAC, expectedMAC)
|
|
}
|
|
}
|
|
return false
|
|
}
|
|
|
|
// Cipher provides methods to encrypt and decrypt cookie values
|
|
type Cipher struct {
|
|
cipher.Block
|
|
}
|
|
|
|
// NewCipher returns a new aes Cipher for encrypting cookie values
|
|
func NewCipher(secret []byte) (*Cipher, error) {
|
|
c, err := aes.NewCipher(secret)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
return &Cipher{Block: c}, err
|
|
}
|
|
|
|
// Encrypt a value for use in a cookie
|
|
func (c *Cipher) Encrypt(value string) (string, error) {
|
|
ciphertext := make([]byte, aes.BlockSize+len(value))
|
|
iv := ciphertext[:aes.BlockSize]
|
|
if _, err := io.ReadFull(rand.Reader, iv); err != nil {
|
|
return "", fmt.Errorf("failed to create initialization vector %s", err)
|
|
}
|
|
|
|
stream := cipher.NewCFBEncrypter(c.Block, iv)
|
|
stream.XORKeyStream(ciphertext[aes.BlockSize:], []byte(value))
|
|
return base64.StdEncoding.EncodeToString(ciphertext), nil
|
|
}
|
|
|
|
// Decrypt a value from a cookie to it's original string
|
|
func (c *Cipher) Decrypt(s string) (string, error) {
|
|
encrypted, err := base64.StdEncoding.DecodeString(s)
|
|
if err != nil {
|
|
return "", fmt.Errorf("failed to decrypt cookie value %s", err)
|
|
}
|
|
|
|
if len(encrypted) < aes.BlockSize {
|
|
return "", fmt.Errorf("encrypted cookie value should be "+
|
|
"at least %d bytes, but is only %d bytes",
|
|
aes.BlockSize, len(encrypted))
|
|
}
|
|
|
|
iv := encrypted[:aes.BlockSize]
|
|
encrypted = encrypted[aes.BlockSize:]
|
|
stream := cipher.NewCFBDecrypter(c.Block, iv)
|
|
stream.XORKeyStream(encrypted, encrypted)
|
|
|
|
return string(encrypted), nil
|
|
}
|