Amiibo Encryption Key -

Because these keys are proprietary Nintendo property, developers cannot include them in their apps without risking legal action.

The amiibo encryption key (often found as key_retail.bin ) is a proprietary cryptographic file required to decrypt and encrypt the data stored on Nintendo amiibo NFC tags. It acts as the "master key" for third-party applications to interact with raw amiibo data. Core Functionality amiibo encryption key