Split non-cipher code to utils.go out of ciphers.go

pkg/encryption/utils.go

@@ -0,0 +1,107 @@
+package encryption
+
+import (
+	"crypto/hmac"
+	"crypto/sha1"
+	"crypto/sha256"
+	"encoding/base64"
+	"fmt"
+	"hash"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// SecretBytes attempts to base64 decode the secret, if that fails it treats the secret as binary
+func SecretBytes(secret string) []byte {
+	b, err := base64.RawURLEncoding.DecodeString(strings.TrimRight(secret, "="))
+	if err == nil {
+		// Only return decoded form if a valid AES length
+		// Don't want unintentional decoding resulting in invalid lengths confusing a user
+		// that thought they used a 16, 24, 32 length string
+		for _, i := range []int{16, 24, 32} {
+			if len(b) == i {
+				return b
+			}
+		}
+	}
+	// If decoding didn't work or resulted in non-AES compliant length,
+	// assume the raw string was the intended secret
+	return []byte(secret)
+}
+
+// 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 []byte, 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 = 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 []byte, now time.Time) string {
+	encodedValue := base64.URLEncoding.EncodeToString(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
+}
+