The aes_keys.txt file is the "skeleton key" for your 3DS emulation experience. While the technical side of encryption can seem daunting, setting up the file is a one-time process that unlocks the entire library of 3DS titles for high-resolution play on your computer.
AES (Advanced Encryption Standard) keys are a set of cryptographic keys used to encrypt and decrypt data. In the context of Citra, AES keys are required to decrypt 3DS game files, allowing users to play them on their computers. The AES keys are stored in a file called aes_keys.txt . Citra Aes Keys.txt Download
Which you are using (Windows, Android, etc.) The aes_keys