M2E.1: parse the EXCHANGE plaintext as Aliro §8.3.3.5 / Table 8-19
[sub_event_id, payload_len, payload], reject SW_WRONG_LENGTH on truncation
or length mismatch and SW_DATA_INVALID on unknown sub_event_id (M2 only
supports 0x01 = ReaderStatusRequest).
M2E.2: emit a Reader Status sub-event RESPONSE (Table 8-20) plaintext
[0x01, 0x00, 0x00] in place in the APDU buffer, GCM-encrypted under
StepUpSKDevice + deviceIv(stepup_device_counter) per §8.3.1.6. Ciphertext+
tag = 19 B, single APDU, no chaining.
Harness verify_step_up_m2 + the test mock now ship the spec request shape,
decrypt the 19 B EXCHANGE response under deviceCounter=1, and decrypt the
subsequent ENVELOPE response under deviceCounter=2 (EXCHANGE consumed 1).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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