Authenticator model identifier in WebAuthn. nixtropic's is self-assigned
(nixtropic + version byte), not registered with the FIDO Alliance.
APDU
Application Protocol Data Unit: a smart-card command or response, carried over CCID.
CCID
USB Chip Card Interface Device class: how a smart-card reader appears on USB. The
OpenPGP card uses it, through pcscd and libccid on the host.
CTAP2 / CTAPHID
FIDO Alliance protocol between the browser (or libfido2) and the authenticator;
CTAPHID is its framing over USB HID.
DFU
USB Device Firmware Upgrade. The STM32's ROM bootloader speaks it; holding SW1
while plugging in enters it.
KEK
Key Encryption Key: a key whose only job is to lock another key. nixtropic's KEK
seals the OpenPGP decryption key and is derived from the PW1 binding, never stored.
L1 / L2 / L3
TROPIC01's protocol layers: SPI transport, CRC-framed requests, and the encrypted
application session.
libtropic
Tropic Square's C SDK for TROPIC01.
MAC-and-Destroy (M&D)
TROPIC01 function: returns 32 bytes that the chip computes from the input and the
slot’s hidden state, and replaces that state with a new one derived from the input.
The basis of chip-enforced PIN retry limits. See
design.
Pairing key
X25519 key pair that opens the encrypted session with TROPIC01. The chip holds up to
four public keys (SH0–SH3); the host side holds the private key. nixtropic uses the
public development key in SH0.
PW1, PW3, Reset Code
OpenPGP card PINs. PW1 is the user PIN (used as 81 for signing and 82 for
decryption and authentication), PW3 the Admin PIN, the Reset Code unblocks PW1.
R-config, I-config
TROPIC01 configuration: rewritable and one-way (bits go only from 1 to 0). Together
they decide which pairing slot may use which command. nixtropic writes neither.
R-memory
TROPIC01's 512 user data slots, encrypted at rest inside the chip.
RDP
STM32 Read-Out Protection: option-byte levels 0, 0.5, 1 and 2 that restrict the
debug port and flash read-out. Level 2 is permanent unless an unlock key was set
beforehand.
Record pair
nixtropic's storage unit: one object in two data slots, written one after the other
and read back, so one fault never grants access or rolls back an acknowledged write
(limits).
SPECT
The TROPIC01's elliptic-curve co-processor; it has its own firmware next to the
chip's RISC-V application firmware.
TS1302
Tropic Square's USB devkit: STM32U535 + TROPIC01 + USB-C, one button, one LED.
UIF
User Interaction Flag: the OpenPGP card's touch policy (uif in gpg).
UV, UP
User verification (a PIN) and user presence (a button press) in FIDO2. alwaysUv
requires the PIN for every credential use.