129 lines
3.6 KiB
Go
129 lines
3.6 KiB
Go
package encryption
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import (
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"crypto/aes"
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"crypto/cipher"
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"crypto/hmac"
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"crypto/rand"
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"crypto/sha1"
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"encoding/base64"
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"fmt"
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"io"
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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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// cookies are stored in a 3 part (value + timestamp + signature) to enforce that the values are as originally set.
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// additionally, the 'value' is encrypted so it's opaque to the browser
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// Validate ensures a cookie is properly signed
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func Validate(cookie *http.Cookie, seed string, expiration time.Duration) (value string, t time.Time, ok 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
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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 {
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return
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}
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// The expiration timestamp set when the cookie was created
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// isn't sent back by the browser. Hence, we check whether the
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// creation timestamp stored in the cookie falls within the
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// window defined by (Now()-expiration, Now()].
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t = time.Unix(int64(ts), 0)
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if t.After(time.Now().Add(expiration*-1)) && t.Before(time.Now().Add(time.Minute*5)) {
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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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value = string(rawValue)
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ok = true
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return
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}
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}
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}
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return
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}
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// SignedValue returns a cookie that is signed and can later be checked with Validate
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func SignedValue(seed string, key string, value string, now time.Time) string {
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encodedValue := base64.URLEncoding.EncodeToString([]byte(value))
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timeStr := fmt.Sprintf("%d", 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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// Cipher provides methods to encrypt and decrypt cookie values
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type Cipher struct {
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cipher.Block
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}
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// NewCipher returns a new aes Cipher for encrypting cookie values
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func NewCipher(secret []byte) (*Cipher, error) {
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c, err := aes.NewCipher(secret)
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if err != nil {
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return nil, err
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}
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return &Cipher{Block: c}, err
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}
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// Encrypt a value for use in a cookie
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func (c *Cipher) Encrypt(value string) (string, error) {
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ciphertext := make([]byte, aes.BlockSize+len(value))
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iv := ciphertext[:aes.BlockSize]
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if _, err := io.ReadFull(rand.Reader, iv); err != nil {
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return "", fmt.Errorf("failed to create initialization vector %s", err)
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}
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stream := cipher.NewCFBEncrypter(c.Block, iv)
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stream.XORKeyStream(ciphertext[aes.BlockSize:], []byte(value))
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return base64.StdEncoding.EncodeToString(ciphertext), nil
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}
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// Decrypt a value from a cookie to it's original string
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func (c *Cipher) Decrypt(s string) (string, error) {
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encrypted, err := base64.StdEncoding.DecodeString(s)
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if err != nil {
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return "", fmt.Errorf("failed to decrypt cookie value %s", err)
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}
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if len(encrypted) < aes.BlockSize {
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return "", fmt.Errorf("encrypted cookie value should be "+
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"at least %d bytes, but is only %d bytes",
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aes.BlockSize, len(encrypted))
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}
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iv := encrypted[:aes.BlockSize]
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encrypted = encrypted[aes.BlockSize:]
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stream := cipher.NewCFBDecrypter(c.Block, iv)
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stream.XORKeyStream(encrypted, encrypted)
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return string(encrypted), nil
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}
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