3DS ROM images can be in either encrypted or unencrypted form. ... Citra only works with decrypted images, so any encrypted image needs to be decrypted first.

What type of ROM do I need for Citra?

3DS and . CIA ROMs, which are the default file type supported by the actual handheld 3DS console. You have to properly decrypt them first before you can run them on Citra Emulator. There are sites offering decrypted 3DS ROMs for free.

What is the difference between encrypted and decrypted ROM?

3DS ROM images can be in either encrypted or unencrypted form. Typically, homebrew images would be unencrypted while backups of retail titles would be encrypted. Citra only works with decrypted images, so any encrypted image needs to be decrypted first.