Tapsigner is an inexpensive Bitcoin signing device that holds your private keys on an NFC card. As of writing this, nunchuck is the only mobile wallet to support it.
Backups of the private key are done so in a AES-128-CTR encryption using a key printed on the back of the card.
To decrypt this key and obtain its xprv value with openssl in cli run the following:
openssl aes-128-ctr -iv 0 -K "<BACKUP_KEY_ON_CARD>" -in backup.aes