Blizzard Entertainment’s Diablo II used a 26-character alphanumeric key (format: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX). Unlike modern online authentication, the game primarily relied on offline checksum validation.

[Your Name] Course/Journal: Game Security & Digital Rights Management

This paper examines the structure and verification logic of 26-character CD keys used in Diablo II (2000) and its expansion. It outlines the checksum algorithm, character set restrictions, and how offline validation was implemented to prevent casual piracy. The study also discusses known vulnerabilities that led to key generators and modern implications for legacy software authentication.

I notice you're looking for a paper related to "Diablo 2 CD key 26 digit." However, that specific query seems more like a game-related technical reference (likely for classic Diablo II or the Lord of Destruction expansion, which used 26-character keys) rather than an academic or research topic.