diff --git a/index.js b/index.js
index 5595ef4..2b7034d 100644
--- a/index.js
+++ b/index.js
@@ -23,7 +23,7 @@ const TYPE_MOBI = 'application/x-mobipocket-ebook'
 const allowedTypes = [TYPE_EPUB, TYPE_MOBI, 'application/pdf', 'application/vnd.comicbook+zip', 'application/vnd.comicbook-rar', 'text/html', 'text/plain', 'application/zip', 'application/x-rar-compressed']
 const allowedExtensions = ['epub', 'mobi', 'pdf', 'cbz', 'cbr', 'html', 'txt']
 
-const keyChars = "3469ACEGHLMNPRTY"
+const keyChars = "23456789ACDEFGHJKLMNPRSTUVWXYZ"
 const keyLength = 4