6.3 Amazon Sidewalk BLE security

The Amazon Sidewalk security model, architecture and certificate chain are described in Chapter 4, section 4.1, section 4.1.1, section 4.1.2. The frame structure is described in section 4.8. The key structure and names, key exchange and authentication procedure are the same as those described for sub-GHz technology in section 4.5. The following sections of the document focus on the differences in implementation for the specificity of the BLE medium (high bandwidth and available frame length 255 B). The procedures for synchronization, registration and authentication of an Endpoint in the Amazon Sidewalk system are described in Chapter 4, and in section 4.2 and section 4.4.2.2.

6.3.1 Amazon Sidewalk Application Layer credentials

Detailed specification for the Amazon Sidewalk Application Layer credentials for Network Server and Application Server are presented in the following subsections.

6.3.1.1 Network Server Encryption/Decryption

Counter-based credentials are used only after a factory reset when an Endpoint has not yet synchronized time. Time-based credentials are used for regular data traffic.

Symmetric keys with 128 bit length are used for coding the Network Server link. Authentication tag is 4 B size. Initialization vector is 12 B length. Additional Authentication Data are a concatenation of Flex parameters listed in Table 6.2 below.

Table 6.2 Encryption and Decryption parameters

Credentials	Time-based Commands	Counter-based Commands	Registration (Touchless FFN / Mobile)
Key type	GCM_KEY	GCM_CTRREF_KEY	GCM_CTRREF_KEY
Authentication tag	4B	4B	4B
AAD	1B Flex Header length FLEX_KEY_LL_SEQ_NUM FLEX_KEY_SRC_FRMT | FLEX_KEY_SRC FLEX_KEY_DST_FRMT | FLEX_KEY_DST FLEX_KEY_ENCR_ENA FLEX_KEY_PROTOCOL_VER FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED	1B Flex Header length FLEX_KEY_LL_SEQ_NUM FLEX_KEY_SRC_FRMT | FLEX_KEY_SRC FLEX_KEY_DST_FRMT | FLEX_KEY_DST FLEX_KEY_ENCR_ENA FLEX_KEY_PROTOCOL_VER FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED	1B Flex Header length FLEX_KEY_LL_SEQ_NUM FLEX_KEY_SRC_FRMT | FLEX_KEY_SRC FLEX_KEY_DST_FRMT | FLEX_KEY_DST FLEX_KEY_ENCR_ENA FLEX_KEY_PROTOCOL_VER FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED
IV	5B Source ID | 2b Link type 22b Sequence number | 4B Reference time	5B Source ID | 2b Link type 22b Sequence number | 4B counter reference	5B Source ID | 2b Link type 22b Sequence number | 4B counter reference

Link type: 0x0 = Radio, 0x1 = BLE

6.3.1.2 Counter-based network server security

Counter-based network security is used in the registration procedure and the deregistration procedure when an Endpoint has not yet synchronized time. Payload is processed according to the formula:

AES-GCM (Encrypted Payload, AAD, IV, Authentication TAG, GCM_CTRREF_KEY)

where

GCM_CTRREF_KEY = CMAC(NETWORK_PRIMARY_KEY, "Network KDF Dev Ntw GCM COUNTER" | Counter Reference)

and Counter Reference = Counter value supplied in the flex header.

6.3.1.3 Network Server Authentication parameters (Only TIME_SYNC command)

Counter-based time synchronization (TIME_SYNC command) is used when an Endpoint reboots and/or over the periodic time sync.

The only difference between the time-based and counter-based time sync commands is the key type used. Details are presented in Table 6.3.

Table 6.3 BLE key types

Credentials	Time-based	Counter-based
Key type	TSYNC_RESP_KEY (Not Supported)	TSYNC_RESP_CTRREF_KEY
Authentication Tag (MAC) size	4B	4B
IV (Initialization Vector)	None	None
AAD (Additional Authentication Data)	1B Flex Header length FLEX_KEY_LL_SEQ_NUM | FLEX_KEY_SRC_FRMT FLEX_KEY_SRC | FLEX_KEY_DST_FRMT FLEX_KEY_DST | FLEX_KEY_ENCR_ENA FLEX_KEY_PROTOCOL_VER FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY | FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED	1B Flex Header length FLEX_KEY_LL_SEQ_NUM | FLEX_KEY_SRC_FRMT FLEX_KEY_SRC | FLEX_KEY_DST_FRMT FLEX_KEY_DST | FLEX_KEY_ENCR_ENA FLEX_KEY_PROTOCOL_VER FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY | FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED

6.3.2 Application Server Encryption/Decryption

AES-CTR cryptography is used for Application Server data processing. Details are presented in Table 6.4.

Table 6.4 Encryption/Decryption parameters

Credentials	Time based	Registration
Key type	APP_CTR_KEY	APP_GCM_CTRREF_KEY
AAD (Additional Authentication Data)	NONE	1B Flex Header length | FLEX_KEY_LL_SEQ_NUM FLEX_KEY_SRC_FRMT | FLEX_KEY_SRC | FLEX_KEY_DST_FRMT FLEX_KEY_DST | FLEX_KEY_ENCR_ENA FLEX_KEY_PROTOCOL_VER | FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY | FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED | 2B - 4B of plain text ASL header
Authentication Tag (MAC) size	NONE	4B
IV (Initialization Vector)	5B Source ID | 1b uplink/downlink | 7b Zeros 2B app layer seqn | 4B time reference | 4B Zeros Source ID: Component generating the packet UL: Sidewalk ID DL: Cloud component generating the packet 1b uplink/downlink: 1 = uplink, 0 = downlink 4B Zeros: Padding to align 16Bytes IV	5B Source ID | 1b Link type | 7b null 2B app layer seqn | 4B counter reference Source ID: Component generating the packet UL: Sidewalk ID DL: Cloud component generating the packet (Provisioning Service) link type: 1 = uplink, 0 = downlink

6.3.3 D2D-related parameters

D2D feature uses a security procedure similar to that used for registration. D2D_PRIMARY_KEY is used for mobile to Endpoint communication. Derived keys with their credentials and derivation method are in Table 6.5.

Table 6.5 Device to device keys

Credentials	D2D_GCM_KEY	D2D_GCM_CTRREF_KEY
Key type	time based	counter based
Authentication tag	4B	4B
AAD	1B Flex Header length | FLEX_KEY_LL_SEQ_NUM FLEX_KEY_SRC_FRMT | FLEX_KEY_SRC FLEX_KEY_DST_FRMT | FLEX_KEY_DST FLEX_KEY_ENCR_ENA | FLEX_KEY_PROTOCOL_VER FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY | FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED	1B Flex Header length | FLEX_KEY_LL_SEQ_NUM FLEX_KEY_SRC_FRMT | FLEX_KEY_SRC FLEX_KEY_DST_FRMT | FLEX_KEY_DST FLEX_KEY_ENCR_ENA | FLEX_KEY_PROTOCOL_VER FLEX_KEY_SEC_REF_COUNTER_VAL FLEX_KEY_SEC_TOPOLOGY | FLEX_KEY_SEC_REF FLEX_KEY_IS_DATA_ASL_FORMATTED
IV	5B Source ID | 2b Link type 22b Sequence number | 4B counter reference	5B Source ID | 2b Link type 22b Sequence number | 4B counter reference
Key derivation	CMAC(D2D_PRIMARY_KEY, "Mobile KDF Device Mobile GCM" | time reference for this key)	CMAC(D2D_PRIMARY_KEY, "Mobile KDF Device Mobile GCM COUNTER" | [0x00, 0x00, 0x00, 0x00])