Verify Encrypted Counters (M/Chip 4)

Command:

Validate an encrypted counter that the issuer may optionally include in Issuer Application Data.

Notes:

Diagnostic data is produced by this command only if the HSM is in Authorised State. The issuer may include the following offline counters in Issuer Application data:

· Offline Cumulative Transaction Amount (OCTA) (6 bytes).

· Offline Consecutive Transaction Number (OCTN) (1 byte).

The issuer may optionally choose that these counters be encrypted. This command will validate the Encrypted Counter data and decrypt the counters.

Field	Length & Type	Details
COMMAND MESSAGE
Message Header	m A	(Subsequently returned to the Host unchanged).
Command Code	2 A	Value K0
Scheme-ID	1 N	Identifier for the Scheme: 0 = M/Chip 4
*MK-AC(LMK)	32H or 1A+32H	The Issuer Master Key for Application Cryptograms encrypted under Variant 1 of LMK pair 28-29.
PAN/PAN Sequence No	8B	Pre-formatted PAN/PAN Sequence No.
Branch/Height parameters	1N	0 = Branch factor 2; Tree Height 16 1 = Branch factor 4; Tree Height 8
Application Transaction Counter	2B	The ATC from the card. This is used for Session Key Generation.
Encrypted Counters	8B	The Encrypted Counter data, containing the OCTA and OCTN
End Message Delimiter	1C	Optional. Must be present if the message trailer is present. Value X’19
Message Trailer	NA	Optional. Maximum length 32 characters

Field	Length & Type	Details
RESPONSE MESSAGE
Message Header	MA	Will be returned to the Host unchanged
Response Code	2A	Value “K1”
Error Code	2N	00 – No error 01 – Encrypted Counter verification failed 10 – MK parity error 12 – No keys in user storage 13 – LMK parity error 15 – Error in input data 21 – Invalid user storage index
OCTA	6B	Offline Cumulated Transaction Amount
OCTN	1B	Offline Consecutive Transaction Number
End Message Delimiter	1C	Will only be present if present in the command message. Value X’19.
Message Trailer	n A	Will only be present if in the command message. Maximum length 32 characters.