Chapter 18: Baseline Privacy Interface (BPI)
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Further information can be obtained from CableLabs
®
in the latest versions of the DOCSIS Baseline Privacy and Baseline
Privacy Plus Interface specifications.
BPI Operations
Baseline Privacy is comprised of two separate but interrelated protocols. The first is Baseline Privacy Key Management
(BPKM), the second is the packet data encryption on the RF link.
Baseline Privacy Key Management (BPKM)
The CM and C4/c CMTS use the BPKM protocol to determine authorization status and transfer of traffic encrypted data.
Through this key management protocol, the CM and C4/c CMTS synchronize keying information. BPKM follows a
client/server model where the CM, the client, requests encryption data and the C4/c CMTS, the server, responds to those
requests. BPKM uses DOCSIS MAC Management messaging in the request/reply operations of the BPKM protocol. Baseline
Privacy uses public-key cryptography to establish symmetric traffic keys between the CM and C4/c CMTS.
Packet Data Encryption
Packet data encryption is an extended service within the DOCSIS® MAC sublayer. When encrypting packet data, only the
frame’s packet data is encrypted; the frame’s header is not encrypted. To indicate the proper encryption/decryption key to
use, a special Baseline Privacy Extended Header is included in the MAC frame header. This special extended header
indicates encryption information related to the current MAC frame. Currently the C4/c CMTS supports 56-bit DES
operating in cipher block chaining (CBC) mode.
Note: To reduce confusion in MIB tables and the Baseline Privacy Specification, a Security Association ID (SAId) can be
thought of as the key ID for a traffic flow. It is just a number and should not be confused with the SID which is the service
ID of an upstream service flow.
Baseline Privacy Operational Overview
The operation between the CM and C4/c CMTS is conducted in three main steps:
Registration