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X-CUBE-ALIRO firmware sends ENVELOPE (CLA=0x00 INS=0xC3) carrying the encrypted mdoc DeviceRequest after the step-up AID SELECT. Spec §8.3.1.9 defines the inbound IV (reader-side: 0x0000000000000000 || stepup_reader_counter). For Milestone 1 we decrypt-and-discard the DeviceRequest, then return a spec-shape encrypted empty CBOR map (1 plaintext byte 0xA0, GCM-encrypted with StepUpSKDevice using device-side IV per §8.3.1.6: 0x0000000000000001 || stepup_device_counter). Total response: 17 bytes (1 ct + 16 tag). Adds stepUpDeviceCounter[4] CLEAR_ON_DESELECT alongside the existing stepUpReaderCounter; both init to [0,0,0,1] when StepUpApplet.select() derives session keys (i.e. each Step-Up phase entry). Restructures the StepUpApplet dispatch so CLA=0x00 ENVELOPE coexists with CLA=0x80 EXCHANGE -- ENVELOPE uses the ISO-standard CLA per spec/ISO 7816 convention, EXCHANGE remains Aliro-proprietary. M2 will replace the empty CBOR map with a real mdoc DeviceResponse carrying the cached-verified Access Document bytes. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>