.CIA File Extension
What is a CIA file?
A CIA file is a CTR Importable Archive used to install game content to a Nintendo 3DS handheld device. It contains game content, TMD (title metadata), and a ticket (encrypted titlekey). CIA files are commonly used for installing gamecard updates and mainly store 3DS eShop content.
The CIA format structure is similar to the .WAD format used by the Wii console. The sections that make up a CIA file are the certificate chain, ticket, TMD file data, content file data, and meta file data.
How to open a CIA file
Those looking to read and extract data from CIA files can do using ctrtool (Windows) or GodMode9 (Nintendo 3DS). Those looking to install decrypted CIA files within a Nintendo 3DS emulator can do so using Citra (cross-platform). To install a CIA file in Citra, select File → Install CIA from the program's menu bar.