107 lines
3.1 KiB
Go
107 lines
3.1 KiB
Go
package encryption
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import (
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"crypto/hmac"
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"crypto/sha1"
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"crypto/sha256"
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"encoding/base64"
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"fmt"
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"hash"
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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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// SecretBytes attempts to base64 decode the secret, if that fails it treats the secret as binary
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func SecretBytes(secret string) []byte {
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b, err := base64.RawURLEncoding.DecodeString(strings.TrimRight(secret, "="))
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if err == nil {
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// Only return decoded form if a valid AES length
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// Don't want unintentional decoding resulting in invalid lengths confusing a user
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// that thought they used a 16, 24, 32 length string
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for _, i := range []int{16, 24, 32} {
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if len(b) == i {
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return b
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}
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}
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}
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// If decoding didn't work or resulted in non-AES compliant length,
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// assume the raw string was the intended secret
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return []byte(secret)
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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 []byte, 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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if checkSignature(parts[2], seed, cookie.Name, parts[0], parts[1]) {
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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 = 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 []byte, now time.Time) string {
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encodedValue := base64.URLEncoding.EncodeToString(value)
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timeStr := fmt.Sprintf("%d", now.Unix())
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sig := cookieSignature(sha256.New, 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(signer func() hash.Hash, args ...string) string {
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h := hmac.New(signer, []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 checkSignature(signature string, args ...string) bool {
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checkSig := cookieSignature(sha256.New, args...)
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if checkHmac(signature, checkSig) {
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return true
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}
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// TODO: After appropriate rollout window, remove support for SHA1
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legacySig := cookieSignature(sha1.New, args...)
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return checkHmac(signature, legacySig)
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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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