• Citra needs AES keys to decrypt ROMs.
• keys.txt stores those keys and must be placed in user/keys/ for portable mode.
• Portable is activated via an empty portable.txt file.
• Legality demands you dump your own keys from a 3DS you own.

For Citra to work in a portable mode, where it's run from a directory (such as a folder on a USB drive) without installation, several conditions need to be met:

Warning: This article does not host or provide direct links to keys. You must extract them from hardware you own. citra aes keystxt portable