add zero-padding to base32 decoding for odd-length totp secrets

1 files changed, 9 insertions, 9 deletions

diff --git a/kasi-totp.el b/kasi-totp.el
index b8fe078..a237ef7 100644
--- a/kasi-totp.el
+++ b/kasi-totp.el
@@ -5,8 +5,8 @@
 ;; https://github.com/juergenhoetzel/emacs-totp
 ;; https://github.com/grimnebulin/emacs-hmac
 (require 'bindat)
-(require 'hexl)
 (require 'cl-lib)
+(require 'hexl)
 (require 'subr-x)
 
 (defconst hmac-algorithm-blocksizes
@@ -56,17 +56,17 @@ string."
   "The cheats' version of base-32 decode.
 
 This is not a 100% faithful implementation of RFC 4648. The
-concept of encoding partial quanta is not implemented fully.
-
-No attempt is made to pad the output either as that is not
-required for HMAC-TOTP."
+concept of encoding partial quanta is not implemented fully."
   (unless (mod (length string) 8)
     (error "Padding is incorrect"))
   (setq string (upcase string))
-  (let ((trimmed-array (append (string-trim-right string "=+") nil)))
-    (format "%X" (seq-reduce
-                  (lambda (acc char) (+ (ash acc 5) (aref base32-alphabet char)))
-                  trimmed-array 0))))
+  (let* ((trimmed-array (append (string-trim-right string "=+") nil))
+         (hex (format "%X" (seq-reduce
+                           (lambda (acc char) (+ (ash acc 5) (aref base32-alphabet char)))
+                           trimmed-array 0))))
+    (if (cl-oddp (length hex))
+        (concat "0" hex)
+      hex)))
 
 (defun totp--hex-decode-string (string)
   "Hex-decode STRING and return the result as a unibyte string."