oauth2_proxy/pkg/encryption/cipher.go
2019-06-08 07:46:06 +01:00

129 lines
3.6 KiB
Go

package encryption
import (
"crypto/aes"
"crypto/cipher"
"crypto/hmac"
"crypto/rand"
"crypto/sha1"
"encoding/base64"
"fmt"
"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
}
sig := cookieSignature(seed, cookie.Name, parts[0], parts[1])
if checkHmac(parts[2], sig) {
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(seed, key, encodedValue, timeStr)
cookieVal := fmt.Sprintf("%s|%s|%s", encodedValue, timeStr, sig)
return cookieVal
}
func cookieSignature(args ...string) string {
h := hmac.New(sha1.New, []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 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
}