We introduce DigitalSeal, a transaction authentication tool that works in both online and offline use scenarios. DigitalSeal is a digital scanner that reads transaction information sent by an issuing entity of the DigitalSeal reader for authentication, and the information is encoded using a specially crafted bar-code. DigitalSeal views various pieces of transaction information for users to verify and proceed with transaction authentication. DigitalSeal is generic, and is capable of reading information viewed on paper, computer monitors (similarly, kiosk monitors), and mobile phones. A prototype of DigitalSeal is built using a Arduino UNO, four LLS05-A sensors, four TCRT5000 sensors, a 1602 LCD and a 9V battery.