2.2.3.3 BringUpSuccessResponseUnpaired Message

The BringUpSuccessResponseUnpaired message is sent by the server to the client in response to a BringUpStartRequest message (section 2.2.3.1) when the request for tethering is successful, but there is no pairing relationship between the server and client. Thus, the sensitive content is encrypted.

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header																								HMAC (35 bytes)
...
...
...
...																Initialization Vector (19 bytes)
...
...
...
...								Encrypted Response (variable)
...
...
...

header (3 bytes): The header field contains the CommonHeader structure (section 2.2.2.2), where the value of the Id field is set to 5 (BringUpSuccessResponseUnpaired), as specified in MessageId (section 2.2.1.1), the length of the Length field is variable, and the value MUST be set to the combined size of all structures contained within the message.

HMAC (35 bytes): The HMAC field contains the HMAC structure (section 2.2.2.6), which consists of the header (3 bytes), and 32 bytes containing a SHA-256 hash of the 16-byte initialization vector contained in the Initialization Vector field, the EncryptedBringUpSuccessResponse contained in the Encrypted Response field, and the 8-byte timestamp contained in the Timestamp structure (section 2.2.2.12) sent by the client in the BringUpStartRequest (section 2.2.3.1) message. The hashing key is a 256-bit key (K3) already known by both the server and the client.

Initialization Vector (19 bytes): The Initialization Vector field contains the InitializationVector structure (section 2.2.2.7), which consists of the header (3 bytes) and the 16 randomly generated bytes used by the server to encrypt the EncryptedBringUpSuccessResponse (Encrypted Response) that is also contained in the message.

Encrypted Response (variable): The Encrypted Response field contains the encrypted BringUpSuccessResponse, as defined in the EncryptedBringUpSuccessResponse structure (section 2.2.2.4). The BringUpSuccessResponse is encrypted using AES-256 in CBC mode, with PKCS#7 padding used to encrypt the message. The encryption key is a 256-bit key (K2) already known by both the server and the client. A randomly generated initialization vector is used, and is included in the message as the Initialization Vector field.