Authorization Control Profile

The Elliptic Curve Diffie-Hellman (ECDH) key exchange (also called the ECDH key agreement scheme) shall support the NIST-approved [5] and ENISA-recommended [6] elliptic ‘Curve P-256’ and key derivation function (KDF) ‘HKDF SHA-256 128-bit’ based on HMAC-SHA-256 as described in [1].

If the AC Server supports confidentiality, integrity, and authentication by setting the value of 1 to the corresponding bits in the Protection_Methods field of the ACS Feature characteristic, the AC Server shall support Galois/Counter Mode (GCM) authenticated encryption. In the case where the AC Server supports authentication and integrity by setting the corresponding bits to a value of 1 and setting the corresponding bit for confidentiality to a value of 0, the AC Server shall use the Galois/Counter Mode Message Authentication Code (GMAC) variant of GCM for authenticated messaging.

The initialization vector (IV) used for GCM and GMAC shall be a fixed field concatenated with an invocation field. The size of the IV fixed field shall be 4 octets. The size of the IV invocation field shall be 8 octets. The IV invocation field shall be implemented as a ‘Sequence Number Different Fixed Parts’.

The ECDH key exchange shall support the NIST-approved [5] and ENISA-recommended [6] elliptic ‘Curve P-256’ and key derivation function ‘HKDF SHA-256 128-bit’ based on HMAC-SHA-256 as described in ACS [1].

The AC Client shall confirm the exchange of the ECDH public key using either No Confirmation OOB Method Used, Confirmation Output OOB Number Action Used, Confirmation Input OOB Number Action Used, or Confirmation Static OOB Number Used as supported by the AC Server. When the AC Client requests the start of the key exchange, the AC Client shall include the selected method to be used.

If the AC Client selects an output action, the AC Client shall prompt the user to input the Output OOB Number provided by the AC Server.

If the AC Client selects an input action, the AC Client shall generate a random Input OOB Number to be observed by the user and entered into the AC Server as described in the selected input action.

ACS [1] defines the algorithms and parameters to calculate the AC Client confirmation code used to confirm the exchanged key.

In the context of the ACS Data Out characteristics, a response to the ACS Data In characteristic request may be segmented. If the AC Client receives a response on an ACS Data Out characteristic that identifies additional segments are remaining, that response is considered to have timed out if the additional segment is not received within the Attribute Protocol (ATT) transaction timeout period, defined as 30 seconds, from the last segment received. If a timeout occurs, the AC Client shall consider the response to have failed.

Table 5.4 shows the requirements for the AC Client to support ACS CP opcodes in the context of this profile.

To get all of the active descriptors (i.e., current restriction map descriptor, information security configuration descriptor, and key descriptor), the AC Client shall write the Get All Active Descriptors opcode with no operand to the ACS CP characteristic.

Writing the Get All Active Descriptors opcode to the ACS CP characteristic triggers the execution of the following AC Server procedures:

See Appendix D for an example of the data flow for the Get All Active Descriptors procedure.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with an operand containing a Request Opcode set to the Get All Active Descriptors and a Response Code Value set to Success, which states the successful completion of the procedure requested or an error value as described in Section 5.5.4.23.

To get an unprotected restriction map descriptor, the AC Client shall write the Get Restriction Map Descriptor opcode with an operand containing the desired restriction map ID and resource handle filter criterion to the ACS CP characteristic.

To get a protected restriction map descriptor, the AC Client shall write the Get Restriction Map Descriptor opcode with an operand containing the desired restriction map ID and resource handle filter criterion with applied information security controls to the ACS Data In characteristic.

The AC Client may request to filter the restriction map descriptor by Resource Handle. If a filtered restriction map descriptor is requested, then the AC Server responds with the descriptor records that match the filter criterion. If no records match the filter criterion, then the AC Client receives a Response Code opcode and an operand of the Request Opcode set to Get Restriction Map Descriptor opcode and a Response Code Value set to No Records Found.

If the payload of the Restriction Map Descriptor Response operand exceeds the ATT_MTU size, the AC Client shall behave as described in Section 5.5.1.

The AC Client shall wait (see Section 5.5.4.22) for the last Restriction Map Descriptor Response opcode with an operand containing the last restriction map descriptor record stating the successful completion of the procedure requested or an error value as described in Section 5.5.4.23. For an unprotected restriction map, the response comes from the ACS CP characteristic. For a protected restriction map, the response comes from the ACS Data Out Indicate characteristic with applied information security controls.

To get a list of the available restriction map IDs and their required Information Security Configuration IDs, the AC Client shall write the Get Restriction Map ID List opcode with no operand to the ACS CP characteristic.

The restriction map ID list is an array of entries. Each entry includes a restriction map ID and the required corresponding Information Security Configuration ID to interact with that restriction map (e.g., activating the restriction map or reading out the restriction map descriptor).

If the payload of the Restriction Map ID List Response operand exceeds the ATT_MTU size, the AC Client shall behave as described in Section 5.5.1.

The AC Client shall wait (see Section 5.5.4.22) for the Restriction Map ID List Response opcode with an operand containing restriction map IDs and the corresponding Information Security Configuration IDs stating the successful completion of the procedure requested or an error value as described in Section 5.5.4.23.

To activate an unprotected restriction map, the AC Client shall write the Activate Restriction Map opcode with an operand containing the restriction map ID to be activated to the ACS CP characteristic.

To activate a protected restriction map, the AC Client shall write the Activate Restriction Map opcode with an operand containing the restriction map ID to be activated with applied information security controls to the ACS Data In characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with an operand containing the Requested Opcode set to Activate Restriction Map opcode and a Response Code Value set to Success, which states the successful completion of the procedure requested, or an error value as described in Section 5.5.4.23. For an unprotected restriction map, the response comes from the ACS CP characteristic. For a protected restriction map, the response comes from the ACS Data Out Indicate characteristic with applied information security controls.

To get the map between the AC Server defined Resource Handle and Attribute UUID, the AC Client shall write the Get Resource Handle To UUID Map opcode with no operand to the ACS CP characteristic.

If the payload of the Resource Handle To UUID Map Response operand exceeds the ATT_MTU size, the AC Client shall behave as described in Section 5.5.1.

The AC Client shall wait (see Section 5.5.4.22) for the last Resource Handle To UUID Map Response opcode with an operand containing the last map record stating the successful completion of the procedure requested or an error value as described in Section 5.5.4.23.

To get the service and characteristic UUIDs mapped to a specific AC Server defined Resource Handle, the AC Client shall write the Get Service And Characteristic UUIDs For Characteristic Resource Handle opcode with an operand containing the Resource Handle of a characteristic to the ACS CP characteristic.

If the payload of the Service And Characteristic UUIDs For Characteristic Resource Handle Response operand exceeds the ATT_MTU size, the AC Client shall behave as described in Section 5.5.1.

The AC Client shall wait (see Section 5.5.4.22) for the last Service And Characteristic UUIDs For Characteristic Resource Handle Response opcode with an operand containing the last map record stating the successful completion of the procedure requested or an error value as described in Section 5.5.4.23.

To get the information security configuration descriptor, the AC Client shall write the Get Information Security Configuration Descriptor opcode with an operand containing the information security configuration filter criterion to the ACS CP characteristic.

The AC Client may request to filter the information security configuration descriptor by the Information Security Configuration ID. If a filtered information security configuration descriptor is requested, then the AC Server responds with the descriptor records that match the filter criterion. If no records match the filter criterion, then the AC Client receives a Response Code opcode and an operand of Request Opcode set to Get Information Security Configuration Descriptor opcode and a Response Code Value set to No Records Found.

If the payload of the Information Security Configuration Descriptor Response operand exceeds the ATT_MTU size, the AC Client shall behave as described in Section 5.5.1.

The AC Client shall wait (see Section 5.5.4.22) for the last Information Security Configuration Descriptor Response opcode with an operand containing the last information security configuration descriptor record stating the successful completion of the procedure requested or an error value as described in Section 5.5.4.23.

To get the key descriptor, the AC Client shall write the Get Key Descriptor opcode with an operand containing the key filter criterion to the ACS CP characteristic.

The AC Client may request to filter the key descriptor by key ID. If the AC Client requests to filter the key descriptor, then the AC Server responds with the descriptor records that match the filter criterion. If no records match the filter criterion, then the AC Client receives a Response Code opcode and an operand of Request Opcode set to Get Key Descriptor opcode and a Response Code Value set to No Records Found.

If the payload of the Key Descriptor Response operand exceeds the ATT_MTU size, the AC Client shall behave as described in Section 5.5.1.

The AC Client shall wait (see Section 5.5.4.22) for the last Key Descriptor Response opcode with an operand containing the last key descriptor record stating the successful completion of the procedure requested or an error value as described in Section 5.5.4.23.

To get the current list of IDs of valid keys between the AC Client and the AC Server, the AC Client shall write the Get Current Key List opcode with no operand to the ACS CP characteristic.

If the payload of the Current Key List Response operand exceeds the ATT_MTU size, the AC Client shall behave as described in Section 5.5.1.

The AC Client shall wait (see Section 5.5.4.22) for the last Current Key List Response opcode with an operand containing the last key ID stating the successful completion of the procedure requested or an error value as described in Section 5.5.4.23.

To indicate the start of a key exchange and confirmation, the AC Client shall write the Start Key Exchange opcode with an operand containing the key ID that will be exchanged, the selected confirmation method, and the selected confirmation action to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with the Request Opcode set to Start Key Exchange and the Response Code Value set to Success, which states the successful completion of the procedure requested, or an error value as described in Section 5.5.4.23.

In the case of an error during the key exchange and confirmation, the AC Server responds with the Key Exchange Response opcode and an operand containing the ID of the key and the response code Key Exchange Failed. If the AC Client wants to retry the key exchange procedure after an error, then the AC Client shall do so from the beginning (i.e., write the Start Key Exchange opcode with an operand to the ACS CP characteristic) because no recovery procedure is defined.

For further details on exchanging keys, the corresponding ACS CP procedure, example data flows, and test vectors, see ACS [1].

Upon successful key exchange and confirmation, the AC Client shall wait (see Section 5.5.4.22) for the Key Exchange Response opcode with an operand containing the ID of the key and the response code Key Exchanged Successful.

To invalidate all of the established security for all AC Clients (e.g., expired exchanged keys), the AC Client shall write the Invalidate All Established Security opcode with no operand to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with the Response Code Value set to Success, which states the successful reception of the procedure requested, or an error value as described in Section 5.5.4.23.

To invalidate a key for the requesting AC Client, the AC Client shall write the Invalidate Key opcode followed by an operand consisting of the Key_ID field to the ACS CP characteristic.

The AC Client may request that an exchanged key, a derived key, or all keys for the requesting AC Client be invalidated by setting the value of the Key_ID field to the specific key or to 0xFFFF. If no records match the key ID included in the request, then the AC Client will receive a Response Code opcode and the operand of the Request Opcode set to Invalidate Key opcode and the Response Code Value set to No Records Found.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with the Response Code Value set to Success, which states the successful reception of the procedure requested, or an error value as described in Section 5.5.4.23.

To abort a procedure that the AC Client initiated, the AC Client shall write the Abort opcode with no operand to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with the Response Code Value set to Success, which states the successful aborting of the procedure, or an error value as described in Section 5.5.4.23. Although the AC Server stops the data transfer after the AC Server sends the Response Code Value of Success, the AC Server might still have some records queued for transfer. The queued records might be sent before the transfer is fully terminated. The AC Client might choose to process or ignore these additional responses.

The Request Opcode in the operand of the Response Code opcode is used to determine if the AC Server response is received in response to an Abort procedure or to the procedure that the Abort procedure is trying to abort. If the Abort procedure is completed successfully, then the AC Client receives the Response Code notification with the Request Opcode in the operand set to Abort but will not receive a response for the aborted procedure.

The AC Client may also receive a Response Code opcode with the Request Opcode in the operand set to Abort and the Response Code Value representing an error condition that occurred in processing the request. Though in practice not all Response Code Values may be returned for an Abort procedure, an AC Client shall handle receiving all defined Response Code Values in response to this procedure.

To enable or disable ACS information security controls, the AC Client shall write the Set Security Controls Switch opcode followed by an operand consisting of the Switch_State field to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with the Response Code Value set to Success, which states the successful completion of the procedure requested, or an error value as described in Section 5.5.4.23.

To receive a Uniform Resource Identifier (URI) to request the AC Server key OOB, the AC Client shall write the Get Key URI opcode with an operand containing the key ID to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Key URI Response opcode with an operand containing the key URI, stating successful completion of the procedure requested, or an error value as described in Section 5.5.4.23.

To get the features of the AC Server, the AC Client shall write the Get ACS Feature opcode with no operand to the ACS CP characteristic.

The AC Client shall request the Get ACS Feature procedure to determine the supported features of the AC Server to interpret the supported functionalities, the protection methods provided by the AC Server, the possible out-of-band (OOB) key exchange methods, and the input and output (I/O) capabilities of the AC Server. The provided information allows the AC Client to operate efficiently.

The protection methods defined by the AC Server describe the type of information security controls that are supported by the AC Server.

The I/O capabilities of the AC Server could be used as part of a key exchange confirmation to help protect against man-in-the-middle attacks.

The AC Client shall wait (see Section 5.5.4.22) for the ACS Feature Response opcode with an operand containing the ACS Feature, stating successful completion of the procedure requested, or an error value as described in Section 5.5.4.23.

To set the AC Client nonce fixed, the AC Client shall write the Set AC Client Nonce Fixed opcode and an operand containing the key ID and AC Client nonce fixed value to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with an operand containing the Requested Opcode set to Set AC Client Nonce Fixed opcode and a Response Code Value set to Success stating the successful completion of the procedure requested, or an error value as described in Section 5.5.4.23.

To get the negotiated ATT_MTU value from the AC Server, the AC Client shall write the Get ATT_MTU opcode with no operand to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the ATT_MTU Response opcode with an operand containing the (ATT_MTU – 3) value stating successful completion of the procedure requested, or an error value as described in Section 5.5.4.23.

To initiate the pairing procedure described in the Bluetooth Core Specification, v4.2 or later [2], the AC Client shall write the Initiate Pairing opcode with no operand to the ACS CP characteristic.

The AC Client shall wait (see Section 5.5.4.22) for the Response Code opcode with the Response Code Value set to Success stating receiving the procedure requested, or an error value as described in Section 5.5.4.23.

In the context of the CP characteristic, a procedure begins when the AC Server sends the write response to the AC Client write request. The procedure is considered to be completed when the CP characteristic responds with an indication of either an opcode set to Response Code or an opcode set to the corresponding response of the procedure followed by the required operand.

A procedure is considered to have timed out if a notification is not received within the ATT transaction timeout period, defined as 30 seconds, from the start of the procedure or from the last notification that was received as a result of the procedure.

If the link is lost while a CP procedure is in progress, the procedure shall be considered to have timed out.

If the AC Client writes an opcode to the CP characteristic and the AC Client Characteristic Configuration descriptor of the CP is not configured for indications, the AC Server will send an ATT Error Response with the Error Code set to AC Client Characteristic Configuration Descriptor Improperly Configured. To execute the procedure associated with the opcode, the AC Client shall configure the AC Client Characteristic Configuration descriptor of the CP characteristic for indications and may write the opcode to the CP characteristic again.

If the AC Client writes an opcode to the CP characteristic that is not supported by the AC Server (i.e., an RFU value) or does not refer to a feature (i.e., not an optional opcode), then the AC Server will send a Response Code opcode response with the Response Code Value set to Opcode Not supported.

If the AC Client writes an operand to the CP characteristic that is invalid (e.g., invalid structure, field with RFU value), then the AC Server will send a Response Code opcode response with the Response Code Value set to Invalid Operand.

If the AC Client writes to the CP characteristic and the procedure cannot be completed for any reason, then the AC Server will send a Response Code opcode response with the Response Code Value set to Procedure Not Completed.

If the AC Client writes any opcode, with the exception of the Abort opcode, to the CP characteristic procedure, and another CP procedure is running, the AC Server will send an ATT Error Response with the error code set to Procedure Already in Progress, and the AC Client should wait until the procedure completes before executing a new procedure.

If the AC Client writes to the CP characteristic and the procedure is protected, then the AC Server will send an ATT Error Response with the Error Code set to Insufficient Authorization.

If the AC Client writes an operand to the CP characteristic that contains a field with a value that is outside the range of values supported by the AC Sever, then the AC Server will send a Response Code opcode response with a Response Code Value set to Parameter Out Of Range.

If the AC Client writes to the CP characteristic and the procedure cannot be executed because the procedure is not applicable in the current AC Server context or the procedure refers to a feature that is not supported by the AC Server (i.e., the corresponding feature bit is not set in the ACS Feature characteristic Features field or an optional opcode is not supported), the AC Server will send a Response Code opcode response with the Response Code Value set to Procedure Not Applicable.

If the AC Client writes the Abort opcode to the CP characteristic and the running procedure cannot be aborted for any reason not stated in this section, then the AC Server will send a Response Code opcode response with a Response Code Value set to Abort Unsuccessful.

If the AC Client writes an operand to the CP characteristic that requests records that do not exist on the AC Server, then the AC Server will send a Response Code opcode response with a Response Code Value set to No Records Found.

If the AC Client writes a confirmation random number that does not correspond to the previously written confirmation code, then the AC Server will send a Response Code opcode response with a Response Code Value set to Invalid Key Exchange Confirmation Code.

If the AC Client writes an invalid public key, then the AC Server will send a Response Code opcode with a Response Code Value set to Invalid Public Key.

The AC Client behavior in the case of a received error, as described in this section, is left to the implementation.