SNIP_CLASSIC_SECOC_SECTION_7_1_2_Authentication_of_I_PDUs

7.1.2 Authentication of I-PDUs [SWS_SecOC_00031]⌈ The creation of a Secured I-PDU and thus the authentication of an Authentic I- PDUconsists of the following six steps: 1. Prepare Secured I-PDU 2. Construct Data for Authenticator 3. Generate Authenticator 4. Construct Secured I-PDU 5. Increment Freshness Counter 6. Broadcast Secured I-PDU ⌋(SRS_SecOC_00006) [SWS_SecOC_00033]⌈ The SecOC module shall prepare the Secured I-PDU. During preparation,SecOC shall allocate the necessary buffers to hold the intermediate and final results of the authentication process. ⌋(SRS_SecOC_00006) [SWS_SecOC_00034]⌈ The SecOC module shall construct the DataToAuthenticator, i.e. the data that is used to calculate the Authenticator. DataToAuthenticator is formed by concatenating the full 16 bit representation of the Data Id (parameter SecOCDataId), the secured part of the Authentic I-PDU and the complete Freshness Value corresponding to SecOCFreshnessValueID in the given order. The Data Id and the Freshness Value shall be encoded in Big Endian byte order for that purpose. ⌋(SRS_SecOC_00006) [SWS_SecOC_00035]⌈ The SecOC module shall generate the Authenticator by passing DataToAuthenticator, length of DataToAuthenticator into the Authentication Algorithm corresponding to SecOCTxAuthServiceConfigRef. ⌋(SRS_SecOC_00006) [SWS_SecOC_00036]⌈ The SecOC module shall truncate the resulting Authenticator down to the number of bits specified by SecOCAuthInfoTruncLength. ⌋(SRS_SecOC_00006) [SWS_SecOC_00037]⌈ The SecOC module shall construct the Secured I-PDU by adding the Secured I-PDU Header (optional), the Freshness Value (optional) and the Authenticator to the Authentic I-PDU. The scheme for the Secured I-PDU (includes the order in which the contents are structured in the Secured I-PDU) shall be compliant with below: SecuredPDU = SecuredIPDUHeader (optional) | AuthenticIPDU | FreshnessValue [SecOCFreshnessValueTruncLength] (optional) | Authenticator [SecOCAuthInfoTruncLength] ⌋(SRS_SecOC_00006) Note: The Freshness Counter and the Authenticator included as part of the Secured I-PDU may be truncated per configuration specific to the identifier of the Secured I-PDU. Also, Freshness Value may be a part of Authentic I-PDU (see [SWS_SecOC_00219]).