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ANNEX I CU.K. Requirements for construction, testing, installation, and inspection
Appendix 11
COMMON SECURITY MECHANISMS U.K.
PART BU.K. SECOND-GENERATION TACHOGRAPH SYSTEM
10.VU- CARD MUTUAL AUTHENTICATION AND SECURE MESSAGINGU.K.
10.5. Secure Messaging U.K.
10.5.1 General U.K.
CSM_181All commands and responses exchanged between a vehicle unit and a tachograph card after successful Chip Authentication took place and until the end of the session shall be protected by Secure Messaging.U.K.
CSM_182Except when reading from a file with access condition SM-R-ENC-MAC-G2 (see Appendix 2, section 4), Secure Messaging shall be used in authentication-only mode. In this mode, a cryptographic checksum (a.k.a. MAC) is added to all commands and responses to ensure message authenticity and integrity.U.K.
CSM_183When reading data from a file with access condition SM-R-ENC-MAC-G2, Secure Messaging shall be used in encrypt-then-authenticate mode, i.e. the response data is encrypted first to ensure message confidentiality, and afterwards a MAC over the formatted encrypted data is calculated to ensure authenticity and integrity.U.K.
CSM_184Secure Messaging shall use AES as defined in [AES] with the session keys KMAC and KENC that were agreed during Chip Authentication.U.K.
CSM_185An unsigned integer shall be used as the Send Sequence Counter (SSC) to prevent replay attacks. The size of the SSC shall be equal to the AES block size, i.e. 128 bits. The SSC shall be in MSB-first format. The Send Sequence Counter shall be initialized to zero (i.e. ‘00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00’) when Secure Messaging is started. The SSC shall be increased every time before a command or response APDU is generated, i.e. since the starting value of the SSC in a SM session is 0, in the first command the value of the SSC will be 1. The value of SSC for the first response will be 2.U.K.
CSM_186For message encryption, KENC shall be used with AES in the Cipher Block Chaining (CBC) mode of operation, as defined in [ISO 10116], with an interleave parameter m = 1 and an initialization vector SV = E(KENC, SSC), i.e. the current value of the Send Sequence Counter encrypted with KENC.U.K.
CSM_187For message authentication, KMAC shall be used with AES in CMAC mode as specified in [SP 800-38B]. The length of the MAC shall be linked to the length of the AES session keys, as specified in CSM_50. The Send Sequence Counter shall be included in the MAC by prepending it before the datagram to be authenticated.U.K.
10.5.2 Secure Message Structure U.K.
CSM_188Secure Messaging shall make use only of the Secure Messaging data objects (see [ISO 7816-4]) listed in Table 5. In any message, these data objects shall be used in the order specified in this table.U.K.
| Table 5 | |||
| Secure Messaging Data Objects | |||
| Data Object Name | Tag | Presence (M)andatory, (C)onditional or (F)orbidden in | |
|---|---|---|---|
| Commands | Responses | ||
| Plain value not encoded in BER-TLV | ‘81’ | C | C |
| Plain value encoded in BER-TLV, but not including SM DOs | ‘B3’ | C | C |
| Padding-content indicator followed by cryptogram, plain value not encoded in BER-TLV | ‘87’ | C | C |
| Protected Le | ‘97’ | C | F |
| Processing Status | ‘99’ | F | M |
| Cryptographic Checksum | ‘8E’ | M | M |
Note: As specified in Appendix 2, tachograph cards may support the READ BINARY and UPDATE BINARY command with an odd INS byte (‘B1’ resp. ‘D7’). These command variants are required to read and update files with more than 32 768 bytes or more. In case such a variant is used, a data object with tag ‘B3’ shall be used instead of an object with tag ‘81’. See Appendix 2 for more information.U.K.
CSM_189All SM data objects shall be encoded in DER TLV as specified in [ISO 8825-1]. This encoding results in a Tag-Length-Value (TLV) structure as follows:U.K.
:
The tag is encoded in one or two octets and indicates the content.
:
The length is encoded as an unsigned integer in one, two, or three octets, resulting in a maximum length of 65 535 octets. The minimum number of octets shall be used.
:
The value is encoded in zero or more octets
CSM_190APDUs protected by Secure Messaging shall be created as follows:U.K.
The command header shall be included in the MAC calculation, therefore value ‘0C’shall be used for the class byte CLA.
As specified in Appendix 2, all INS bytes shall be even, with the possible exception of odd INS bytes for the READ BINARY and UPDATE BINARY commands.
The actual value of Lc will be modified to Lc' after application of secure messaging.
The Data field shall consist of SM data objects.
In the protected command APDU the new Le byte shall be set to ‘00’. If required, a data object ‘97’ shall be included in the Data field in order to convey the original value of Le.
[F1CSM_191 Any data object to be encrypted shall be padded according to [ISO 7816-4] using padding-content indicator ‘01’. For the calculation of the MAC, data objects in the APDU shall be padded according to [ISO 7816-4]. U.K.
Note: Padding for Secure Messaging is always performed by the secure messaging layer, not by the CMAC or CBC algorithms. U.K.
Textual Amendments
Summary and Examples U.K.
A command APDU with applied Secure Messaging will have the following structure, depending on the case of the respective unsecured command (DO is data object):
:
CLA INS P1 P2 || Lc' || DO ‘ 8E ’ || Le
:
CLA INS P1 P2 || Lc' || DO ‘ 97 ’ || DO ‘ 8E ’ || Le
:
CLA INS P1 P2 || Lc' || DO ‘ 81 ’ || DO ‘ 8E ’ || Le
:
CLA INS P1 P2 || Lc' || DO ‘ B3 ’ || DO ‘ 8E ’ || Le
:
CLA INS P1 P2 || Lc' || DO ‘ 81 ’ || DO ‘ 97 ’ || DO ‘ 8E ’ || Le
:
CLA INS P1 P2 || Lc' || DO ‘ B3 ’ || DO ‘ 97 ’ || DO ‘ 8E ’ || Le
where Le = ‘ 00’ or ‘00 00 ’ depending on whether short length fields or extended length fields are used; see [ISO 7816-4].
A response APDU with applied Secure Messaging will have the following structure, depending on the case of the respective unsecured response:
:
DO ‘ 99 ’ || DO ‘ 8E ’ || SW1SW2
:
DO ‘ 81 ’ || DO ‘ 99 ’ || DO ‘ 8E ’ || SW1SW2
:
DO ‘ 87 ’ || DO ‘ 99 ’ || DO ‘ 8E ’ || SW1SW2
:
DO ‘ B3 ’ || DO ‘ 99 ’ || DO ‘ 8E ’ || SW1SW2
Note: Case 2 or 4 (odd INS byte) with encryption is never used in the communication between a VU and a card. U.K.
Below are three example APDU transformations for commands with even INS code. Figure 8 shows an authenticated Case 4 command APDU, Figure 9 shows an authenticated Case 1/Case 3 response APDU, and Figure 10 shows an encrypted and authenticated Case 2/Case 4 response APDU.
Figure 10 Transformation of an encrypted and authenticated Case 2/Case 4 Response APDU U.K.
10.5.3 Secure Messaging Session Abortion U.K.
CSM_192A vehicle unit shall abort an ongoing Secure Messaging session if and only if one of the following conditions occur:U.K.
it receives a plain response APDU,
it detects a Secure Messaging error in a response APDU:
An expected Secure Messaging data object is missing, the order of data objects is incorrect, or an unknown data object is included.
A Secure Messaging data object is incorrect, e.g. the MAC value is incorrect, the TLV structure is incorrect or the padding indicator in tag ‘87’ is not equal to ‘01’.
the card sends a status byte indicating it detected an SM error (see CSM_194),
the limit for the number of commands and associated responses within the current session is reached. For a given VU, this limit shall be defined by its manufacturer, taking into account the security requirements of the hardware used, with a maximum value of 240 SM commands and associated responses per session.
[F1CSM_193 A tachograph card shall abort an ongoing Secure Messaging session if and only if one of the following conditions occur: U.K.
it receives a plain command APDU,
it detects a Secure Messaging error in a command APDU:
An expected Secure Messaging data object is missing, the order of data objects is incorrect, or an unknown data object is included.
A Secure Messaging data object is incorrect, e.g. the MAC value is incorrect or the TLV structure is incorrect.
it is depowered or reset,
the VU starts the VU Authentication process,
the limit for the number of commands and associated responses within the current session is reached. For a given card, this limit shall be defined by its manufacturer, taking into account the security requirements of the hardware used, with a maximum value of 240 SM commands and associated responses per session.]
CSM_194Regarding SM error handling by a tachograph card:U.K.
If in a command APDU some expected Secure Messaging data objects are missing, the order of data objects is incorrect or unknown data objects are included, a tachograph card shall respond with status bytes ‘69 87’.
If a Secure Messaging data object in a command APDU is incorrect, a tachograph card shall respond with status bytes ‘69 88’.
In such a case, the status bytes shall be returned without using SM.
CSM_195If a Secure Messaging session between a VU and a tachograph card is aborted, the VU and the tachograph card shallU.K.
securely destroy the stored session keys
immediately establish a new Secure Messaging session, as described in sections 10.2 — 10.5.